WO2024186735A1 - Methods and compositions for the treatment of cancer - Google Patents

Abstract

Provided herein are methods of treating leptomeningeal metastasis in a subject, the method comprising administering to the subject a viral vector encoding at least one interferon peptide and/or at least one interferon peptide. Also provided herein are methods of treating leptomeningeal metastasis in a subject, the method comprising administering to the subject a viral vector encoding IL- 15 and/or IL- 12 or at least one IL- 15 and/or IL 12 peptide.

Description

METHODS AND COMPOSITIONS FOR THE TREATMENT OF CANCER Related Applications This application claims priority to U.S. Provisional Application 63/449,817, filed March 3, 2023, U.S. Provisional Application 63/449,823, filed March 3, 2023, U.S. Provisional Application 63/530,387, filed August 2, 2023, and U.S. Provisional Application 63/530,389, filed August 2, 2023, each of which is incorporated herein by reference in its entirety. Background Spread of cancer cells into the cerebrospinal fluid-filled leptomeninges is known as leptomeningeal metastasis. This form of metastasis has become increasingly common (Kesari et al., Leptomeningeal metastases. Neurol Clin 21, 25-66 (2003)) and is typically fatal within months (Oechsle et al., Prognostic factors and treatment options in patients with leptomeningeal metastases of different primary tumors: a retrospective analysis. J Cancer Res Clin Oncol 136, 1729-1735 (2010)). Under normal physiological conditions, the leptomeningeal space is isolated from the systemic circulation by the blood-cerebrospinal fluid-barrier. This anatomic compartment is hypoxic and contains sparse amounts of metabolic intermediates and micronutrients (Spector et al., A balanced view of the cerebrospinal fluid composition and functions: Focus on adult humans. Exp Neurol 273, 57- 68 (2015)). In the setting of leptomeningeal metastasis, the normally acellular cerebrospinal fluid contains cancer cells as well as lymphocytes, macrophages and neutrophils. Cancer cells within this microenvironment must therefore cope with oppressive metabolic constraints while evading immune responses. The use of CNS irradiation and targeted therapies, when available, have resulted in prolongation in overall survival in patients with leptomeningeal metastases. However, once these agents have been exhausted, the efficacy of conventional chemotherapy and intrathecal agents to control intracranial disease is quite limited. Accordingly, there is a need for novel agents in the treatment of leptomeningeal metastases. SUMMARY In some aspects, provided herein are methods of treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for at least one IL-12 peptide, and/or a viral vector that encodes for at least one IL-15 peptide, and/or a viral vector that encodes for at least one interferon peptide. In other aspects, provided herein are methods of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer (e.g., a subject is afflicted with leptomeningeal metastasis), the method comprising administering to the subject a viral vector that encodes for at least one IL-12 peptide, or a viral vector that encodes for at least one IL-15 peptide, and/or a viral vector that encodes for at least one interferon peptide. In some embodiments, the viral vector is an adeno associated viral vector (e.g., an AAV5 vector). In some embodiments, the viral vector targets the meninges. In some embodiments, the viral vector targets the choroid plexus. The at least one interferon peptide may be a gamma interferon peptide or an alpha interferon peptide. In some embodiments, the at least one interferon peptide is a modified interferon peptide. In some embodiments, the at least one IL-12 peptide is a modified IL-12. In some embodiments, the at least one IL-15 peptide is a modified IL-15. In some embodiments, the IL-12 peptide is a IL-12 subunit or fragment thereof. In some embodiments, the viral vector is administered intrathecally. In some embodiments, the method further comprises administering an immune checkpoint inhibitor to the subject. In some embodiments, the immune checkpoint inhibitor is an inhibitor of an immune checkpoint protein selected from CTLA-4, PD-1, VISTA, B7- H2, B7-H3, PD-L1, B7-H4, B7-H6, ICOS, HVEM, PD-L2, CD160, gp49B, PIR-B, KIR family receptors, TIM-1, TIM-3, TIM-4, LAG-3, BTLA, SIRPalpha (CD47), CD48, 2B4 (CD244), B7.1, B7.2, ILT-2, ILT-4, TIGIT, HHLA2, butyrophilins, A2aR, and combinations thereof. The immune checkpoint inhibitor is an inhibitor of PD-1 or PD-L1. In some embodiments, the at least one interferon peptide and the immune checkpoint inhibitor are administered conjointly. In some embodiments, the cancer is a lung cancer, a breast cancer, a colon cancer, a cervical cancer, a pancreatic cancer, a renal cancer, a stomach cancer, a GI cancer, a liver cancer, a bone cancer, a hematological cancer, a neural tissue cancer, a melanoma, a thyroid cancer, a ovarian cancer, a testicular cancer, a prostate cancer, a cervical cancer, a vaginal cancer, or a bladder cancer. In some embodiments, the cancer comprises a tumor. The tumor may be an adenocarcinoma, an adrenal tumor, an anal tumor, a bile duct tumor, a bladder tumor, a bone tumor, a brain/CNS tumor, a breast tumor, a cervical tumor, a colorectal tumor, an endometrial tumor, an esophageal tumor, an Ewing tumor, an eye tumor, a gallbladder tumor, a gastrointestinal, a kidney tumor, a laryngeal or hypopharyngeal tumor, a liver tumor, a lung tumor, a mesothelioma tumor, a multiple myeloma tumor, a muscle tumor, a nasopharyngeal tumor, a neuroblastoma, an oral tumor, an osteosarcoma, an ovarian tumor, a pancreatic tumor, a penile tumor, a pituitary tumor, a primary tumor, a prostate tumor, a retinoblastoma, a Rhabdomyosarcoma, a Salivary gland tumor, a soft tissue sarcoma, a melanoma, a metastatic tumor, a basal cell carcinoma, a Merkel cell tumor, a testicular tumor, a thymus tumor, a thyroid tumor, a uterine tumor, a vaginal tumor, a vulvar tumor, or a Wilms tumor. In some aspects, provided herein are methods and compositions for treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for IL-12 and/or IL-15. In other aspects, provided herein are methods of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for IL-12 and/or IL-15. In some embodiments, the viral vector encodes for IL-12. In some embodiments, the viral vector encodes for IL-15. In some embodiments, the viral vector encodes for IL-12 and IL-15. In some embodiments, a viral vector that encodes for IL-12 is administered conjointly with a viral vector that encodes for IL-15. Provided herein are methods and compositions for treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject at least one IL-12 peptide, at least one 1L-15 peptide, and/or at least one interferon peptide. Also provided herein are methods of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer (e.g., a subject is afflicted with leptomeningeal metastasis), the method comprising administering to the subject at least one IL-12 peptide, at least one 1L- 15 peptide, and/or at least one interferon peptide. In some embodiments, the at least one IL-12 or IL-15 peptide is a modified IL-12 or IL-15 peptide. In some embodiments, the IL-12 peptide is a IL-12 subunit or fragment thereof. The at least one interferon peptide may be a gamma interferon peptide or fragment thereof. In some embodiments, the at least one interferon peptide is an alpha interferon peptide. In some embodiments, the at least one interferon peptide is a modified interferon peptide (e.g., a PEGylated interferon peptide). In some embodiments, the peptide is administered intrathecally. In some embodiments, the method further comprises administering an immune checkpoint inhibitor to the subject. For example, the immune checkpoint inhibitor may be an inhibitor of an immune checkpoint protein selected from CTLA-4, PD-1, VISTA, B7-H2, B7-H3, PD-L1, B7-H4, B7-H6, ICOS, HVEM, PD-L2, CD160, gp49B, PIR-B, KIR family receptors, TIM- 1, TIM-3, TIM-4, LAG-3, BTLA, SIRPalpha (CD47), CD48, 2B4 (CD244), B7.1, B7.2, ILT-2, ILT-4, TIGIT, HHLA2, butyrophilins, A2aR, and combinations thereof. In some embodiments, the immune checkpoint inhibitor is an inhibitor of PD-1 or PD-L1. In some embodiments, the at least one peptide and the immune checkpoint inhibitor are administered conjointly. The cancer may be any cancer, including, but not limited to, lung cancer, a breast cancer, a colon cancer, a cervical cancer, a pancreatic cancer, a renal cancer, a stomach cancer, a GI cancer, a liver cancer, a bone cancer, a hematological cancer, a neural tissue cancer, a melanoma, a thyroid cancer, an ovarian cancer, a testicular cancer, a prostate cancer, a cervical cancer, a vaginal cancer, or a bladder cancer. The cancer may comprise a tumor (e.g., a solid tumor). In some embodiments, the tumor is an adenocarcinoma, an adrenal tumor, an anal tumor, a bile duct tumor, a bladder tumor, a bone tumor, a brain/CNS tumor, a breast tumor, a cervical tumor, a colorectal tumor, an endometrial tumor, an esophageal tumor, an Ewing tumor, an eye tumor, a gallbladder tumor, a gastrointestinal, a kidney tumor, a laryngeal or hypopharyngeal tumor, a liver tumor, a lung tumor, a mesothelioma tumor, a multiple myeloma tumor, a muscle tumor, a nasopharyngeal tumor, a neuroblastoma, an oral tumor, an osteosarcoma, an ovarian tumor, a pancreatic tumor, a penile tumor, a pituitary tumor, a primary tumor, a prostate tumor, a retinoblastoma, a Rhabdomyosarcoma, a Salivary gland tumor, a soft tissue sarcoma, a melanoma, a metastatic tumor, a basal cell carcinoma, a Merkel cell tumor, a testicular tumor, a thymus tumor, a thyroid tumor, a uterine tumor, a vaginal tumor, a vulvar tumor, or a Wilms tumor. In some aspects, provided herein are methods of treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject IL-12 and/or IL-15. In other aspects, provided herein are methods of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer, the method comprising administering to the subject IL-12 and/or IL-15. Brief Description of the Drawings Fig.1 shows inflammation-induced pleocytosis in patients with leptomeningeal metastasis. Figure 1A shows representative images of Giemsa-stained cytospins from cancer patients without (top) and with leptomeningeal metastasis (LM, bottom) with major cell populations indicated as Ly - lymphocyte, Mac - monocyte-macrophage, cc - cancer cell (n = 5 per group, scale bar = 20 μm). Figure 1B shows UMAP projection of human CSF immune cell types and cancer cells, isolated from cancer patients without (n = 3 patients and n = 1,196 cells) and with (n = 5 patients and n = 16,022 cells) LM. LM+ samples were retrieved from GSE150660 and colored by cell type. See also Fig.7. Figure 1C shows embedding density plots from LM- and LM+ patients, showing relative cell type abundance per condition, projected onto UMAP. Figure 1D shows relative CSF IFN-γ levels in cancer patients with or without LM from a wide array of solid tumors, as determined by proximity extension assay (LM- n = 49, LM+ n = 61). NPX - normalized protein expression. See also Fig.8. Figure 1E shows a Kaplan-Meier plot showing, post- LM diagnosis survival in relation to CSF IFN-γ levels at diagnosis. Logrank test (IFN-γ high n = 29; IFN-γ low n = 32; cut-off NPX = 4). Fig.2 shows host IFN-γ signaling suppresses expansion of immunocompetent mouse LM cells. Fig.2A shows representative images of hematoxylin-stained cytospins from vehicle- (top) and E0771 LeptoM-injected mice (bottom) with major cell populations indicated as Ly - lymphocyte, Mac - monocyte-macrophage, cc - cancer cell (n = 3 per group, scale bar = 50 μm). See Fig.8 for characterization of immunocompetent LeptoM mouse lines. Figure 2B shows UMAP of cellular material isolated from vehicle- and LLC LeptoM-injected mice two weeks after inoculation, subjected to single-cell proteogenomic profiling with 10x CITE-seq (n = 7,528 cells from vehicle-injected and n = 19,534 cells from LLC LeptoM-injected mice, n = 6 animals per group). Cell type annotations are provided in Fig.10, and experiment overview is provided in Fig.19. Figure 2C shows embedding density plots from LM- and LM+ mice, showing relative cell type abundance per condition, projected onto UMAP. Figure 2D shows levels of IFN-γ in the CSF collected from naïve or LeptoM-bearing mice, detected by cytometric bead array. Figure 2E shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates brain surface area covered with pigmented B16 LeptoM cells delivered intracisternally into C57BL/6 Ifng-proficient and -deficient animals, quantified two weeks after injection. Figure 2F shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates brain surface area covered with pigmented B16 LeptoM cells delivered intracisternally into C57BL/6 Ifngr1-proficient and -deficient animals, quantified two weeks after injection. Photographs show the involvement of mouse basilar meninges with plaques of B16 LeptoM melanoma cells (scale bar = 5 mm). Fig.3 shows IFN-γ controls the growth of metastatic cancer in leptomeninges independent of the adaptive immune system and monocyte-macrophages. Figure 3A shows a representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of E0771 LeptoM cells delivered intracisternally into C57Bl/6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. Figure 3B shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of LLC LeptoM cells delivered intracisternally into C57Bl/6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. Figure 3C shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates brain surface area covered with pigmented B16 LeptoM cells delivered intracisternally into C57BL/6 animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. Figure 3D shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of EMT6 LeptoM cells delivered intracisternally into BALB/c animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. Figure 3E shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of 4T1 LeptoM cells delivered intracisternally into BALB/c animals overexpressing Egfp or Ifng in the leptomeninges, quantified one week after injection. Figure 3F shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of Yumm5.2 LeptoM cells delivered intracisternally into C57Bl6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges, quantified three weeks after injection. Figure 3G shows in vivo radiance of LLC LeptoM cells delivered intracisternally into NSG animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. (NSG - non-obese, diabetic, severe combined immunodeficient, Il2rg^null). Figure 3H shows in vivo radiance of LLC LeptoM cells delivered intracisternally into Rag1-deficient animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. (NSG - non-obese, diabetic, severe combined immunodeficient, Il2rg^null). Figure 3I shows representative immunofluorescent image of brain tissue from cancer-naïve animals overexpressing Egfp or Ifng in the leptomeninges, stained for Iba1⁺ myeloid cells (scale bar = 50 μm). Box plot illustrates quantification of Iba1⁺ cells in the ventricular choroid plexi. Figure 3J shows in vivo radiance of LLC LeptoM cells delivered intracisternally into C57Bl6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges and tri-weekly infused with non-targeting isotype control antibody or CSF1R-targeting antibody, quantified two weeks after injection. Fig.4 shows leptomeningeal IFN-γ supports cDC maturation. Figure 4A shows in vivo radiance of LLC LeptoM cells delivered intracisternally into C57Bl6-Tyr^c-2 bone marrow chimeras overexpressing Egfp or Ifng in the leptomeninges after administration of diphteria toxin. Host mice were infused with bone marrow from wild-type or Zbtb46- DTR^+/+ C57Bl6 mice. Depletion efficiency is quantified in Fig.18. Figure 4B shows dot plot showing expression of characteristic dendritic cell (DC) surface proteins and Ccr7 gene, as determined with single-cell proteogenomics (dendritic cells pooled from 4 conditions, and 6 mice per condition were included; see Fig.19-21 for details). Figure 4C shows tSNE projection of mouse leptomeningeal DC types with predicted maturation streamlines from vehicle- and LLC LeptoM-injected mice two weeks after inoculation, subjected to 10x CITE-seq (total of n = 7,566 cells pooled from 4 conditions and n = 6 animals per group). cDC and pDC cells shown in Fig.19 were subsetted and reclustered, and tSNE was built in multiscale space derived from diffusion components, see Methods. Figure 4D shows expression trends in genes associated with cDC2 identity, IFN-γ signaling, and CCR7+ identity, along diffusion pseudotime axis representing cDC2-CCR7+ DC maturation. Gene trends were computed with Palantir. See also Fig.20 and 21, and Methods. Figure 4E shows a UMAP projection of identity (left) and cell cycle phase prediction (right) in LLC LeptoM cancer cells, isolated from animals overexpressing Egfp or Ifng in the leptomeninges (n = 3,161 and n = 557 cells from Egfp or Ifng-overexpressing mice, respectively; n = 6 animals per group). Cancer cells were identified as keratin- and CD63-expressing cluster and visualized without additional re-clustering, see Fig.10 and 19. Figure 4F shows quantification of LLC LeptoM gene expression-based cell cycle prediction from 4E. See also Fig.22A to 22C. Predictions were computed using scores of gene lists characteristic for S and G2/M phases, see Methods. Figure 4G shows representative immunofluorescent image of E0771 LeptoM cancer plaques in animals overexpressing Egfp or Ifng in the leptomeninges, stained for cleaved Caspase 3 (scale bar = 50 μm). For quantification see Fig.22D to 22F. Fig.5 shows cDC-derived cytokines mediate NK cell activity and proliferation to prevent cancer cell outgrowth. Figure 5A shows a tSNE projection of mouse leptomeningeal natural killer (NK) cell states from vehicle- and LLC LeptoM-injected mice two weeks after inoculation, subjected to 10x CITE-seq (total of n = 2,247 cells from 4 conditions, n = 6 animals per group). Nk1.1⁺ NKG7⁺ CD3- TCRβ- cells from Fig.19 were subsetted and reclustered, and tSNE was built in multiscale space derived from diffusion components, see Methods. Figure 5B shows expression of cell state-enriched NK surface proteins in mouse, as determined with single-cell proteogenomics. Figure 5C shows NK cell cycle prediction in vehicle-injected, cancer-naïve or LLC LeptoM-bearing animals overexpressing Egfp or Ifng in the leptomeninges, as determined with single-cell proteogenomics. Predictions were computed using scores of gene lists characteristic for S and G2/M phases, see Methods. Figure 5D shows smoothened gene expression of selected CCR7+ DC ligands and NK cell receptors, projected onto tSNE plots. Gene imputation was performed with Markov affinity-based graph imputation of cells (MAGIC). Figure 5E shows paired analysis of NK cell survival in human LM- CSF without or with addition of recombinant mouse IL12 and IL15 (results pooled from four independent replicates, paired t test). Figure 5F shows relative abundance of IL12, IL15, and IL18 in the CSF of LM- and LM+ cancer patients, as determined with targeted proteomics. Figure 5G shows expression of cell state-enriched human NK surface proteins, as determined with single-cell transcriptomics. For annotation see Fig.23D to 23F. Figure 5H shows in vivo radiance of LLC LeptoM cells delivered intracisternally into C57Bl6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges and bi-weekly infused with non-targeting isotype control antibody or asialo-GM1-targeting antibody, quantified two weeks after injection. Figure 5I shows in vivo radiance of LLC LeptoM cells delivered intracisternally into C57BL/6 Ifngr1-proficient and -deficient animals and bi-weekly infused with non-targeting isotype control antibody or asialo-GM1-targeting antibody, quantified two weeks after injection. Figure 5J shows quantification of soluble Granzyme A, Perforin, Granulysin, and sFas in the CSF of LM- and LM+ cancer patients, as determined by cytokine bead arrays. Fig.6 shows leptomeningeal dendritic cells represent the essential IFN-γ target. Figure 6 outlines schematic highlighting the main findings of this study. Leptomeningeal IFN-γ, produced mainly by T and NK cells, supports maturation of conventional DC2 into migratory DCs. These migratory DCs are characterized by the expression of Ccr7 in mouse, and LAMP3 in human. In an antigen-independent manner, these newly raised leptomeningeal migratory DCs produce an array of interleukins that support survival and proliferation of NK cells. NK are the cytotoxic effectors that control the expansion of metastatic cells in leptomeninges. Fig.7 shows single-cell transcriptomics of normal, reactive, and malignant human CSF. Figure 7A shows experimental overview of human CSF single-cell transcriptomics. Single-cell RNA-seq data from five LM+ patients with malignant cytology was retrieved from GSE150660 and integrated with previously unpublished data from three patients with negative cytology and two patients whose CSF contained reactive cells. All samples were processed within the same timeframe. For details, see Methods. Figure 7B shows UMAP of human CSF cells colored by individual patient (n = 20,676 cells from n = 10 patients). Figure 7C shows expression of cell type-specific marker genes in human CSF single-cell dataset. Figure 7D shows UMAP of human CSF immune cell types and cancer cells grouped based on cytology, and UMAPs of individual cytologies projected separately. Normal: n = 3 patients and n = 1,196 cells; Reactive: n = 2 patients and n = 3,458 cells; Malignant: n = 5 patients and n = 16,022 cells. Figure 7E shows a proportion of major cell types in the individual patients. Figure 7F shows cell counts of major cell types in the individual patients. Figure 7G shows inter-patient heterogeneity measured with Shannon entropy in subsampled dataset, where up to 500 cells per patient were randomly selected. For each cell, the Shannon entropy measures the sample diversity of its nearest neighbors in the kNN graph. Figure 7H shows inter-sample heterogeneity measured with Shannon entropy in subsampled dataset. Figure 7I shows inter-sample heterogeneity measured with Shannon entropy in subsampled dataset, averaged per cell type and per patient. Fig.8 shows targeted proteomics with proximity extension assay of inflammatory mediators in human CSF. Figure 8A shows targeted proteomic analysis of 92 inflammatory mediators in CSF of breast cancer patients without and with LM by proximity extension assay (multiple t tests). Figure 8B shows targeted proteomic analysis of 92 inflammatory mediators in CSF of lung cancer patients without and with LM by proximity extension assay (multiple t tests). Figure 8C shows targeted proteomic analysis of 92 inflammatory mediators in CSF of melanoma patients without and with LM by proximity extension assay (multiple t tests). Figure 8D shows overlap of inflammatory mediators significantly enriched in CSF of LM+ patients, plotted per primary cancer type (Venn diagram, top panel). Overview of 15 proteins enriched in CSF from LM+ patients and all three cancer types. Fig.9 shows immunocompetent mouse models of leptomeningeal metastasis. Figure 9A shows overview of cancer cell lines used and generated in this study. Figure 9B shows principal component analysis (PCA) of in vitro transcriptome of Parental (gray, n = 3), LeptoM (purple, n = 3), and BrM1 (orange, n = 3) LLC cells. Retrieved from NCBI GEO ^{GSE83132. Figure 9C shows Kaplan-Meier plot showing survival of C57Bl/6-Tyrc-2} animals overexpressing Egfp in the leptomeninges after delivery of LLC LeptoM cells into cisterna magna (related to Fig.14). Representative brain tissue sections stained with H&E showing colonization of leptomeninges after intracardiac delivery of LLC LeptoM cells (scale bar = 100 μm). mOS - median overall survival. Figure 9D shows principal component analysis (PCA) of in vitro transcriptome of Parental (gray, n = 3) and newly established LeptoM (purple, n = 4), and BrM2 (orange, n = 3) B16 cells. Figure 9E shows Kaplan-Meier plot showing survival of C57Bl/6 animals overexpressing Egfp in the leptomeninges after delivery of B16 LeptoM cells into cisterna magna (related to Fig.14). Representative brain tissue sections stained with H&E showing colonization of leptomeninges after intracardiac delivery of B16 LeptoM cells (scale bar = 100 μm). mOS - median overall survival. Figure 9F shows principal component analysis (PCA) of in vitro transcriptome of Parental (gray, n = 3) and newly established LeptoM (purple, n = 3), and BrM2 (orange, n = 3) Yumm5.2 cells. Figure 9G shows Kaplan-Meier plot showing survival of C57Bl/6 and C57Bl/6-Tyr^c-2 animals overexpressing Egfp in the leptomeninges after delivery of Yumm5.2 LeptoM cells into cisterna magna (related to Fig.14). Representative brain tissue sections stained with H&E showing colonization of leptomeninges after intracardiac delivery of Yumm5.2 LeptoM cells (scale bar = 100 μm). mOS - median overall survival. Figure 9H shows principal component analysis (PCA) of in vitro transcriptome of Parental (gray, n = 3) and newly established LeptoM (purple, n = 5), and BrM2 (orange, n = 3) E0771 cells. Figure 9I shows a Kaplan-Meier plot showing survival of C57Bl/6-Tyr^c-2 animals overexpressing Egfp in the leptomeninges after delivery of E0771 LeptoM cells into cisterna magna (related to fig.14). Representative brain tissue sections stained with H&E showing colonization of leptomeninges after intracardiac delivery of E0771 LeptoM cells (scale bar = 100 μm). mOS - median overall survival. Figure 9J shows a principal component analysis (PCA) of in vitro transcriptome of Parental (gray, n = 3) and newly established LeptoM (purple, n = 3), and BrM2 (orange, n = 3) EMT6 cells. Figure 9K shows a Kaplan-Meier plot showing survival of BALB/c animals overexpressing Egfp in the leptomeninges after delivery of EMT6 LeptoM cells into cisterna magna (related to Fig.14). Representative brain tissue sections stained with H&E showing colonization of leptomeninges after intracardiac delivery of EMT6 LeptoM cells (scale bar = 100 μm). mOS - median overall survival. Figure 9L shows principal component analysis (PCA) of in vitro transcriptome of Parental (gray, n = 3) and newly established LeptoM (purple, n = 3), and BrM2 (orange, n = 3) 4T1 cells. Figure 9M shows Kaplan-Meier plot showing survival of BALB/c animals overexpressing Egfp in the leptomeninges after delivery of 4T1 LeptoM cells into cisterna magna (related to fig.14). Representative brain tissue sections stained with H&E showing colonization of leptomeninges after intracardiac delivery of 4T1 LeptoM cells (scale bar = 100 μm). mOS - median overall survival. Fig.10 shows cell type annotation of mouse leptomeningeal immune cells. Figure 10A shows expression of cell type-specific marker genes in mouse proteogenomic single- cell dataset, as captured with single-cell RNA-seq. Figure 10B shows expression of cell type-specific surface markers in mouse proteogenomic single-cell dataset, as determined with CITE-seq. Fig.11 shows IFN-γ production and response in leptomeninges. Figure 11A shows a proportion of T cells (CD3⁺CD4⁺CD8- vs. CD3⁺CD4-CD8⁺) and NK cells (CD3-Nk1.1⁺) expressing IFN-γ in cells isolated from vehicle- or B16, E0771, and LLC LeptoM-injected mice, determined with flow cytometry. Figure 11B shows expression of IFNG gene in mouse (left) and human (right) single-cell datasets. Figure 11C shows abundance of phosphorylated STAT1 (pSTAT1) in leptomeningeal dendritic cells (MHC II⁺ CD11c⁺), monocyte-macrophages (CD11b⁺Ly6C⁺ and CD11b⁺F4/80⁺), T cells (CD3⁺), and NK cells (Nk1.1⁺), as a proxy for IFN-γ pathway activation in vehicle- and LLC LeptoM-injected mice, determined with flow cytometry. Fig.12 shows leptomeningeal tumor growth in Ifng- and Ifngr1-deficient animals. Figure 12A shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of E0771 LeptoM cells delivered intracisternally into C57BL/6 Ifng-proficient and -deficient animals, quantified two weeks after injection. Figure 12B shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of LLC LeptoM cells delivered intracisternally into C57BL/6 Ifng-proficient and -deficient animals, quantified two weeks after injection. Figure 12C shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of E0771 LeptoM cells delivered intracisternally into C57BL/6 Ifngr1-proficient and -deficient animals, quantified two weeks after injection. Figure 12D shows representative leptomeningeal tissue sections stained with H&E (scale bar = 100 μm). Box plot illustrates in vivo radiance of LLC LeptoM cells delivered intracisternally into C57BL/6 Ifngr1- proficient and -deficient animals, quantified two weeks after injection. Fig.13 shows extracranial tumor growth in Ifng- and Ifngr1-deficient animals. Figure 13A shows volumes of intradermal B16 LeptoM flank tumors in C57BL/6 Ifng- proficient and -deficient animals, quantified two weeks after injection. Figure 13B shows volumes of mammary fat pad E0771 LeptoM tumors in C57BL/6 Ifng-proficient and - deficient animals, quantified four weeks after injection. Figure 13C shows volumes of subcutaneous LLC LeptoM flank tumors in C57BL/6 Ifng-proficient and -deficient animals, quantified three weeks after injection. Figure 13D shows volumes of intradermal B16 LeptoM flank tumors in C57BL/6 Ifngr1-proficient and -deficient animals, quantified two weeks after injection. Figure 13D shows volumes of mammary fat pad E0771 LeptoM tumors in C57BL/6 Ifngr1-proficient and -deficient animals, quantified four weeks after injection. Figure 13F shows volumes of subcutaneous LLC LeptoM flank tumors in C57BL/6 Ifngr1-proficient and -deficient animals, quantified three weeks after injection. Fig.14 shows leptomeninges-specific overexpression of IFN-γ extends survival of LeptoM cells-bearing animals. Figure 14A shows a schematic showing experimental strategy of leptomeningeal Egfp or Ifng overexpression, used for functional experiments in this study. Figure 14B shows levels of IFN-γ in the CSF collected from naïve C57Bl/6 and BALB/c animals overexpressing Egfp or Ifng in the leptomeninges, detected by cytometric bead array. Figure 14C shows a Kaplan-Meier plot showing survival of E0771 LeptoM- bearing C57Bl/6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 14D shows a Kaplan-Meier plot showing survival of LLC LeptoM-bearing C57Bl/6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 14E shows a Kaplan-Meier plot showing survival of B16 LeptoM-bearing C57Bl/6 animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 14F shows a Kaplan-Meier plot showing survival of EMT6 LeptoM-bearing BALB/c animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 14G shows a Kaplan-Meier plot showing survival of 4T1 LeptoM-bearing BALB/c animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 14H shows a Kaplan-Meier plot showing survival of Yumm5.2 LeptoM-bearing C57Bl/6 and C57Bl/6- Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Fig.15 shows a leptomeningeal IFN-γ does not affect morphology of brain parenchyma. Figure 15A shows representative images of brain tissue sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained with Luxol Fast Blue (n = 4 per group, 3 months after AAV introduction, scale bar = 500 μm). Figure 15B shows representative images of brain tissue sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained for astrocyte activation marker GFAP (n = 4 per group, 3 months after AAV introduction, scale bar = 100 μm). Figure 15C shows representative images of brain tissue sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained for microglia marker Iba1 (n = 4 per group, 3 months after AAV introduction, scale bar = 100 μm). Figure 15D shows representative images of brain tissue sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained for neural progenitor marker DCX (n = 4 per group, 3 months after AAV introduction, scale bar = 100 μm). Figure 15E shows representative images of brain tissue sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained for myelinization marker MBP (n = 4 per group, 3 months after AAV introduction, scale bar = 200 μm). Figure 15F shows representative images of brain tissue sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained for marker of mature neurons NeuN (n = 4 per group, 3 months after AAV introduction, scale bar = 200 μm). Figure 15G shows quantification of NeuN⁺ mature neurons per FOV in cortical layers 1-4 (left) and 5-6 (right). See outline in Figure 15F. Fig.16 shows leptomeningeal IFN-γ reduces oligodendrocyte numbers in corpus callosum. Figure 16A shows representative images of corpus callosum sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained for marker of oligodendrocytes Olig2 (n = 4 per group, 3 months after AAV introduction, scale bar = 100 μm). Figure 16B shows quantification of Olig2⁺ oligodendrocytes per FOV in corpus callosum. Figure 16C shows representative images of brain tissue sections from naïve C57Bl/6 animals overexpressing Egfp or Ifng stained for markers of oligodendrocytes Olig2 and CNPase (n = 4 per group, 3 months after AAV introduction, scale bar = 100 μm). Figure 16D shows quantification of Olig2⁺ oligodendrocytes per FOV in cortical and subcortical regions. Corresponding regions are marked in Figure 16C. Figure 16C shows quantification of CNPase⁺ oligodendrocytes per FOV in cortical and subcortical regions. Corresponding regions are marked in panel C. Fig.17 shows leptomeningeal IFN-γ does not require adaptive immune system to suppress metastatic outgrowth. Figure 17A shows in vivo radiance of E0771 LeptoM cells delivered intracisternally into NSG animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. (NSG - non-obese, diabetic, severe combined immunodeficient, Il2rg^null). Figure 17B shows a Kaplan-Meier plot showing survival of LLC LeptoM-bearing NSG animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 17C shows a Kaplan-Meier plot showing survival of E0771 LeptoM-bearing NSG animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 17D shows in vivo radiance of E0771 LeptoM cells delivered intracisternally into Rag1-deficient animals overexpressing Egfp or Ifng in the leptomeninges, quantified two weeks after injection. (NSG - non-obese, diabetic, severe combined immunodeficient, Il2rg^null). Figure 17E shows a Kaplan-Meier plot showing survival of LLC LeptoM-bearing Rag1-deficient animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 17F shows a Kaplan-Meier plot showing survival of E0771 LeptoM-bearing Rag1-deficient animals overexpressing Egfp or Ifng in the leptomeninges (logrank test). Figure 17G shows in vivo radiance of E0771 LeptoM cells delivered intracisternally into C57Bl6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges and tri-weekly infused with non-targeting isotype control antibody or CSF1R-targeting antibody, quantified two weeks after injection. Figure 17H shows in vivo radiance of LLC LeptoM cells delivered intracisternally into C57Bl6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges and bi-weekly infused with control or clodronate liposomes, quantified two weeks after injection. Fig.18 shows a depletion of leptomeningeal cDCs in bone marrow chimeras. Figure 18A shows representative images of dendritic cell marker CD11c in leptomeningeal cancer plaques in wild-type (WT) and Zbtb46-DTR bone marrow chimeras, treated with diphteria toxin (DTx). Mice were injected with LLC LeptoM cells (scale bar = 20 μm). Figure 18B shows representative images of dendritic cell marker CD11c in spleen of wild-type (WT) and Zbtb46-DTR bone marrow chimeras, treated with diphteria toxin (DTx). Mice were injected with LLC LeptoM cells (scale bar = 20 μm). Figure 18C shows quantification of systemic cDC depletion in images from 18B. Fig.19 shows mouse single-cell proteogenomics of naïve and metastasis-bearing, Ifng-overexpressing mice. Figure 19A shows an experimental overview of single cell proteogenomic analysis of mouse leptomeninges. Figure 19B shows UMAP of mouse leptomeningeal cells colored by major cell type (n = 24). Figure 19C shows UMAP of mouse leptomeningeal cells colored by condition (n = 6 mice per group). Figure 19D shows individual UMAPs of mouse leptomeningeal cells per condition. Figure 19E shows individual UMAPs showing representation of six barcodes per condition. Figure 19F shows inter-sample heterogeneity measured with Shannon entropy. For each cell, the Shannon entropy measures the sample diversity of its nearest neighbors in the kNN graph. Figure 19G shows the proportion of major cell types per condition. Figure 19H shows counts of major cell types per condition. Fig.20 shows characterization of leptomeningeal dendritic cells. Figure 20A shows a heatmap showing scaled expression of top 30 genes per mouse DC cell type (one cell type vs. the rest; FC > 2). Figure 20B shows a UMAP projection of DC subtypes detected in human CSF (n = 883 cells); cDC and pDC clusters from Fig.1B were subsetted and replotted. cDC1 cells are CLEC9A⁺XCR1⁺, cDC2 cells are CLEC10A⁺CD1C⁺, pDC cells are IRF7⁺TCF4⁺. Human LAMP3+ migratory dendritic cells are LAMP3⁺CCR7⁺ (orthologous to mouse CCR7+ DC). Figure 20C shows a marker gene expression of human CSF DCs. Figure 20D shows a MAGIC-imputed expression of LAMP3 in human CSF dendritic cells. Figure 20E shows CSF cytology classification of human DC types. Figure 20F shows a dot plot showing gene expression of interleukins, chemokines, chemokine receptors, toll-like receptors, and genes associated with antigen presentation in mouse DC cells, as detected with CITE-seq. Normalized counts were used for computation. Genes not detected with 10x and genes that did not pass filtering steps defined in the Methods were not plotted. Figure 20G shows a dot plot showing gene expression of interleukins, chemokines, chemokine receptors, toll-like receptors, and genes associated with antigen presentation in human DC cells, as detected with scRNA-seq. Normalized counts were used for computation. Genes not detected with 10x and genes that did not pass filtering steps defined in the Methods were not plotted. Fig.21 shows a trajectory analysis of leptomeningeal dendritic cells. Figure 21A shows tSNE maps showing abundance of captured dendritic cell types in naïve and metastasis-bearing, Egfp- or Ifng-overexpressing mice (total of n = 7,566 cells pooled from 4 conditions and n = 6 animals per group). Figure 21B shows a proportion of dendritic cell subtypes per condition. Figure 21C shows counts of dendritic cell subtypes per condition. Figure 21D shows a tSNE projection of dendritic cell surface markers detected with CITE- seq. CD11c - pan-DC marker; Xcr1 - cDC1 marker; CD11b - cDC2 marker; B220 - pDC marker. Figure 21E shows a bivariate plot showing distribution of cell surface Xcr1 and CD11b in leptomeningeal dendritic cell subsets, as detected with CITE-seq. Figure 21F shows a tSNE projection of 2,575 mouse leptomeningeal DCs subsetted for trajectory analysis. Cells are from Egfp-overexpressing, naïve and cancer-bearing mice, and the plots are colored based on cell type and condition. See Methods for further details. Figure 21G shows a tSNE projection of CytoTRACE pseudotime, as determined with CellRank, suggesting that CCR7+ DCs are the terminal state within the subsetted cell population. Figure 21H shows a terminal DC macrostates and computed macrostate membership for each cell, as predicted with CellRank and projected onto a tSNE. While cDC1 cells are restricted to cDC1 membership, cells from cDC2 cluster are gradually acquiring CCR7+ DC membership. Figure 21I shows palantir-computed diffusion pseudotime and CCR7+ DC maturation (branch) probability. Gene trends along this pseudotime axis are plotted in Fig.4D. Figure 21J shows plots show Pearson correlation of pseudotime orderings in Palantir analysis for different parameters (waypoint samplings, number of principal components, and number of K-nearest neighbors) and all cells. DC trajectory analysis, performed as described in Methods, is not sensitive to fluctuations in these parameters. Fig.22 shows characterization of leptomeningeal metastatic cells in Egfp- and Ifng- overexpressing mice. Figure 22A shows quantification of cancer cells captured in the mouse single-cell atlas (n = 3,718 keratin⁺ CD63⁺ cells isolated from n = 6 mice per group); related to Figure 4E, F. Figure 22B shows GSEApy analysis of top 15 Reactome 2022 pathways enriched in cancer cells shown in Fig.5 isolated from Ifng-overexpressing animals and subsetted as described in Fig.4E (DEG cut-off P < 0.01). Figure 22C shows GSEApy analysis of top 15 Reactome 2022 pathways enriched in cancer cells isolated from Egfp-overexpressing animals and subsetted as described in Fig.4E (DEG cut-off P < 0.01). Figure 22D shows quantification of cleaved Caspase 3-positive cells in cancer plaques and clusters, in the leptomeninges of Egfp- or Ifng-overexpressing animals injected with LLC LeptoM cells. Figure 22E shows quantification of cleaved Caspase 3-positive cells in cancer plaques and clusters, in the leptomeninges of Egfp- or Ifng-overexpressing animals injected with E0771 LeptoM cells. Figure 22F shows quantification of cleaved Caspase 3- positive cells in cancer plaques and clusters, in the leptomeninges of Egfp- or Ifng- overexpressing animals injected with B16 LeptoM cells. Fig.23 shows characterization of leptomeningeal NK cells. Figure 23A shows a heatmap showing scaled, zero-centered expression of top 50 genes per mouse NK cell state (one state vs. the rest; n = 2,247 cells total). Mouse NK cells were subsetted from ‘NK cell’ and ‘Proliferative T/NK cell’ clusters (Fig.2B) based on the expression of Nk1.1 (cell surface) and NKG7 (gene), and the lack of CD3 and TCRβ (cell surface). Naïve mouse NK cells are characterized based on single-cell RNA- and CITE-seq as CD62L^high, activated NK cells are CD62L^low, proliferative NK cells are CD62L^low MKI67⁺, and senescent NK cells are CD55⁺ KLGR1⁺. See also Fig.5 and Methods. Figure 23B shows a proportion of NK cell states in naïve and metastasis-bearing, Egfp- or Ifng-overexpressing mice. Figure 23C shows cell counts of NK cell states in naïve and metastasis-bearing, Egfp- or Ifng- overexpressing mice. Figure 23D shows UMAP showing NK cell states in human CSF (n = 763 cells); NKG7+ NK cell cluster from Fig.1B was subsetted. Figure 23E shows a projection of mouse naïve-like NK marker SELL (CD62L) and activated-like marker CXCR6 onto human NK cells (MAGIC-imputed counts are plotted). Figure 23F shows CSF cytology classification of human NK cells. Figure 23G shows a heatmap showing scaled, zero-centered expression of top 50 genes per human NK cell state (one state vs. the rest). Fig.24 shows NK cells are the downstream cytotoxic effectors of leptomeningeal IFN-γ. Figure 24A shows Kaplan-Meier plot showing survival of LLC LeptoM-bearing C57Bl/6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges, depleted with control polyclonal antibody (left graph) or antibody targeting asialo-GM1 (logrank test). Figure 24B shows a Kaplan-Meier plot showing survival of E0771 LeptoM-bearing C57Bl/6-Tyr^c-2 animals overexpressing Egfp or Ifng in the leptomeninges, depleted with control polyclonal antibody (left graph) or antibody targeting asialo-GM1 (logrank test). Figure 24C shows a Kaplan-Meier plot showing survival of B16 LeptoM-bearing C57Bl/6 animals overexpressing Egfp or Ifng in the leptomeninges, depleted with control polyclonal antibody (left graph) or antibody targeting asialo-GM1 in one experiment (logrank test). Figure 24D shows efficiency of systemic asialo-GM1-targeting depletion of NK cells in naïve C57Bl/6 animals, quantified in leptomeninges with flow cytometry. Figure 24E shows the efficiency of systemic asialo-GM1-targeting depletion of NK cells in naïve C57Bl/6 animals, quantified in spleen with flow cytometry. Fig.25 shows LM primary tumor type and patient survival. Fig.26 shows experimental methods exemplified herein. Fig.27 shows that targeted CSF proteomics reveals conserved proinflammatory cytokine signature. Fig.28 shows that CSF interferon-ɣ at diagnosis correlates with overall survival. Fig.29 shows that pleocytosis is a hallmark of leptomeningeal metastasis (LM). Fig.30 shows six new syngeneic mouse LM models. Fig.31 shows that mouse models of LM accurately mimic human disease. Fig.32 shows that host interferon-ɣ pathway controls LM cancer cell growth. Fig.33 shows that host interferon-ɣ pathway does not control cancer cell growth outside the meninges. Fig.34 shows that CSF T cells produce the majority of interferon-ɣ. Fig.35 shows that supplemental interferon-ɣ controls LM cancer cell growth. Fig.36 shows IFN-ɣ function is macrophage independent, but dendritic cell dependent. Fig.37 shows that interferon-ɣ drives cDC2-to-CCR7(+)DC maturation and LM cancer cell apoptosis. Fig.38 shows that IFN-ɣ leads to NK cell proliferation. Fig.39 shows that IFN-ɣ matured CCR7+ DCs induce NK cell survival and proliferation. Fig.40 shows that NK cells are effectors of cDC-orchestrated killing. Fig.41 shows cancer-intrinsic IFN-γ signaling is dispensable for tumor growth in leptomeninges. Fig.41A shows in vitro induction of MHC class I in control (sgLacZ) and two Ifngr2-deficient E0771 LeptoM clones with recombinant IFN-γ. Data pooled from three independent experiments. Figure 41B shows in vitro induction of MHC class I in control (sgLacZ) and two Ifngr2-deficient LLC LeptoM clones with recombinant IFN-γ. Data pooled from three independent experiments. Figure 41C shows in vitro induction of MHC class I in control (sgLacZ) and two Ifngr2-deficient B16 LeptoM clones with recombinant IFN-γ. Data pooled from three independent experiments. Figure 41D shows in vitro proliferation of control (sgLacZ) and two Ifngr2-deficient E0771 LeptoM clones exposed to recombinant IFN-γ. Data pooled from three independent experiments. Fig.41E shows in vitro proliferation of control (sgLacZ) and two Ifngr2-deficient LLC LeptoM clones exposed to recombinant IFN-γ. Data pooled from three independent experiments. Fig.41F shows in vitro proliferation of control (sgLacZ) and two Ifngr2-deficient B16 LeptoM clones exposed to recombinant IFN-γ. Data pooled from three independent experiments. Fig.41G shows in vivo radiance of control (sgLacZ) and two Ifngr2-deficient E0771 LeptoM clones delivered intracisternally into C57Bl/6-Tyr^c-2 animals, quantified three weeks after injection in one in vivo experiment. Fig.41H shows in vivo radiance of control (sgLacZ) and two Ifngr2-deficient LLC LeptoM clones delivered intracisternally into C57Bl/6-Tyr^c-2 animals, quantified two weeks after injection in one in vivo experiment. Fig.41I shows Kaplan-Meier plot illustrating overall survival of control (sgLacZ) and two Ifngr2-deficient B16 LeptoM clones delivered intracisternally into C57Bl/6 mice in one in vivo experiment. Fig.42 shows leptomeningeal IFN-γ-mediated tumor growth suppression is driven by the microenvironment. Fig.42A shows in vitro induction of MHC class I in E0771 LeptoM cells with recombinant IFN-γ. Data pooled from three independent experiments. Fig.42B shows in vitro induction of MHC class I in LLC LeptoM cells with recombinant IFN-γ. Data pooled from three independent experiments. Fig.42C shows in vitro induction of MHC class I in B16 LeptoM cells with recombinant IFN-γ. Data pooled from three independent experiments. Fig.42D shows in vitro proliferation of E0771 LeptoM cells exposed to recombinant IFN-γ. Data pooled from three independent experiments. Fig.42E shows in vitro proliferation of LLC LeptoM cells exposed to recombinant IFN-γ. Data pooled from three independent experiments. Fig.42F shows in vitro proliferation of B16 LeptoM cells exposed to recombinant IFN-γ. Data pooled from three independent experiments. Fig.42G shows in vivo tumor growth of E0771 LeptoM cells in C57Bl/6-Tyr^{c- 2} animals injected weekly with vehicle or two doses of recombinant IFN-γ, as a function of radiance. Fig.42H shows in vivo tumor growth of LLC LeptoM cells in C57Bl/6-Tyr^c-2 animals injected weekly with vehicle or two doses of recombinant IFN-γ, as a function of radiance. Fig.42I shows in vivo tumor growth of B16 LeptoM cells in C57Bl/6 animals injected weekly with vehicle or two doses of recombinant IFN-γ, as a function of radiance. Fig.42J shows in vivo tumor growth of LLC LeptoM cells in C57Bl/6-Tyr^c-2 animals injected weekly with heat-inactivated vehicle (PBS) or heat-inactivated recombinant IFN-γ, as a function of radiance in one in vivo experiment. Fig.43 shows that supplemental interferon-ɣ controls LM cancer cell growth. Detailed Description The present disclosure further provides methods for preventing and/or reducing the risk of leptomeningeal metastasis in a subject having cancer. In certain embodiments, the subject has progressive or recurrent leptomeningeal metastases after anti-cancer therapy and before administration of a viral vector or peptide disclosed herein. In certain embodiments, the subject has progressive leptomeningeal metastases after radiation therapy. Provided herein are methods of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer, the method comprising administering to the subject at least one IL-12, IL-15 or interferon peptide, or a viral vector that encodes for such a peptide. As used herein, “recruiting” includes, but is not limited to, increasing the rate of movement of cells to a target tissue or anatomical area or increasing the amount of cells in a target tissue or anatomical area. “Proliferating” includes, but is not limited to, increasing the absolute or relative number of cells a target tissue or anatomical area. As used herein, “maturing” includes inducing development of an immature cell to an established cell. “Activating” refers to a process of inducing a desired action (e.g., release of cytokines, the secretion of cytolytic granules, or the use of death receptor-mediated cytolysis) of a cell or population of cells. “Increasing the survival of” cells refers to any process where the lifespan of a cells is increased beyond the average or expected lifespan of the cells. Survival can be measured in one cell or within a population of cells. Definitions For convenience, certain terms employed in the specification, examples, and appended claims are collected here. The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. The term “agent” is used herein to denote a chemical compound, a small molecule, a mixture of chemical compounds and/or a biological macromolecule (such as a nucleic acid, an antibody, an antibody fragment, a protein or a peptide). The activity of such agents may render them suitable as a “therapeutic agent” which is a biologically, physiologically, or pharmacologically active substance (or substances) that acts locally or systemically in a subject. Unless otherwise specified here within, the terms “antibody” and “antibodies” broadly encompass naturally-occurring forms of antibodies (e.g. IgG, IgA, IgM, IgE) and recombinant antibodies such as single-chain antibodies, chimeric and humanized antibodies and multi-specific antibodies, as well as fragments and derivatives of all of the foregoing, which fragments and derivatives have at least an antigenic binding site. Antibody derivatives may comprise a protein or chemical moiety conjugated to an antibody. Exemplary antibodies for use herein, include, but are not limited to, immune checkpoint inhibitors. The term “antibody” as used herein also includes an “antigen-binding portion” of an antibody (or simply “antibody portion”). The term “antigen-binding portion”, as used herein, refers to one or more fragments of an antibody that retain the ability to specifically bind to an antigen (e.g., a biomarker polypeptide or fragment thereof). It has been shown that the antigen-binding function of an antibody can be performed by fragments of a full- length antibody. Examples of binding fragments encompassed within the term “antigen- binding portion” of an antibody include (i) a Fab fragment, a monovalent fragment consisting of the VL, VH, CL and CH1 domains; (ii) a F(ab')2 fragment, a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region; (iii) a Fd fragment consisting of the VH and CH1 domains; (iv) a Fv fragment consisting of the VL and VH domains of a single arm of an antibody, (v) a dAb fragment (Ward et al., (1989) Nature 341:544-546), which consists of a VH domain; and (vi) an isolated complementarity determining region (CDR). Furthermore, although the two domains of the Fv fragment, VL and VH, are coded for by separate genes, they can be joined, using recombinant methods, by a synthetic linker that enables them to be made as a single protein chain in which the VL and VH regions pair to form monovalent polypeptides (known as single chain Fv (scFv); see e.g., Bird et al. (1988) Science 242:423-426; and Huston et al. (1988) Proc. Natl. Acad. Sci. USA 85:5879-5883; and Osbourn et al.1998, Nature Biotechnology 16: 778). Such single chain antibodies are also intended to be encompassed within the term “antigen-binding portion” of an antibody. Any VH and VL sequences of specific scFv can be linked to human immunoglobulin constant region cDNA or genomic sequences, in order to generate expression vectors encoding complete IgG polypeptides or other isotypes. VH and VL can also be used in the generation of Fab, Fv or other fragments of immunoglobulins using either protein chemistry or recombinant DNA technology. Other forms of single chain antibodies, such as diabodies are also encompassed. Diabodies are bivalent, bispecific antibodies in which VH and VL domains are expressed on a single polypeptide chain, but using a linker that is too short to allow for pairing between the two domains on the same chain, thereby forcing the domains to pair with complementary domains of another chain and creating two antigen binding sites (see e.g., Holliger et al. (1993) Proc. Natl. Acad. Sci. U.S.A.90:6444-6448; Poljak et al. (1994) Structure 2:1121- 1123). An antibody for use in the instant invention may be a bispecific antibody. A bispecific antibody has binding sites for two different antigens within a single antibody polypeptide. Antigen binding may be simultaneous or sequential. Triomas and hybrid hybridomas are two examples of cell lines that can secrete bispecific antibodies. Examples of bispecific antibodies produced by a hybrid hybridoma or a trioma are disclosed in U.S. Patent 4,474,893. Bispecific antibodies have been constructed by chemical means (Staerz et al. (1985) Nature 314:628, and Perez et al. (1985) Nature 316:354) and hybridoma technology (Staerz and Bevan (1986) Proc. Natl. Acad. Sci. USA, 83:1453, and Staerz and Bevan (1986) Immunol. Today 7:241). Bispecific antibodies are also described in U.S. Patent 5,959,084. Fragments of bispecific antibodies are described in U.S. Patent 5,798,229. Bispecific agents can also be generated by making heterohybridomas by fusing hybridomas or other cells making different antibodies, followed by identification of clones producing and co-assembling both antibodies. They can also be generated by chemical or genetic conjugation of complete immunoglobulin chains or portions thereof such as Fab and Fv sequences. Still further, an antibody or antigen-binding portion thereof may be part of larger immunoadhesion polypeptides, formed by covalent or noncovalent association of the antibody or antibody portion with one or more other proteins or peptides. Examples of such immunoadhesion polypeptides include use of the streptavidin core region to make a tetrameric scFv polypeptide (Kipriyanov et al. (1995) Human Antibodies and Hybridomas 6:93-101) and use of a cysteine residue, biomarker peptide and a C-terminal polyhistidine tag to make bivalent and biotinylated scFv polypeptides (Kipriyanov et al. (1994) Mol. Immunol.31:1047-1058). Antibody portions, such as Fab and F(ab')2 fragments, can be prepared from whole antibodies using conventional techniques, such as papain or pepsin digestion, respectively, of whole antibodies. Moreover, antibodies, antibody portions and immunoadhesion polypeptides can be obtained using standard recombinant DNA techniques, as described herein. Antibodies may also be “humanized,” which is intended to include antibodies made by a non-human cell having variable and constant regions which have been altered to more closely resemble antibodies that would be made by a human cell. For example, by altering the non-human antibody amino acid sequence to incorporate amino acids found in human germline immunoglobulin sequences. The humanized antibodies of the disclosure may include amino acid residues not encoded by human germline immunoglobulin sequences (e.g., mutations introduced by random or site-specific mutagenesis in vitro or by somatic mutation in vivo), for example in the CDRs. The term “humanized antibody”, as used herein, also includes antibodies in which CDR sequences derived from the germline of another mammalian species, such as a mouse, have been grafted onto human framework sequences. The terms “cancer” or “tumor” refer to the presence of cells possessing characteristics typical of cancer-causing cells, such as uncontrolled proliferation, immortality, metastatic potential, rapid growth and proliferation rate, and certain characteristic morphological features. Cancer cells are often in the form of a tumor, but such cells may exist alone within an animal, or may be a non-tumorigenic cancer cell, such as a leukemia cell. As used herein, the term “cancer” includes premalignant as well as malignant cancers. Cancers include, but are not limited to, B cell cancer, e.g., myelomas like multiple myeloma, Waldenström's macroglobulinemia, the heavy chain diseases, such as, for example, alpha chain disease, gamma chain disease, and mu chain disease, benign monoclonal gammopathy, and immunocytic amyloidosis, melanomas, breast cancer, lung cancer, bronchus cancer, colorectal cancer, prostate cancer, pancreatic cancer, stomach cancer, ovarian cancer, urinary bladder cancer, brain or central nervous system cancer, peripheral nervous system cancer, esophageal cancer, cervical cancer, uterine or endometrial cancer, cancer of the oral cavity or pharynx, liver cancer, kidney cancer, testicular cancer, biliary tract cancer, small bowel or appendix cancer, salivary gland cancer, thyroid gland cancer, adrenal gland cancer, osteosarcoma, chondrosarcoma, cancer of hematologic tissues, and the like. Other non-limiting examples of types of cancers applicable to the methods encompassed by the present disclosure include human sarcomas and carcinomas, e.g., fibrosarcoma, myxosarcoma, liposarcoma, chondrosarcoma, osteogenic sarcoma, chordoma, angiosarcoma, endotheliosarcoma, lymphangiosarcoma, lymphangioendotheliosarcoma, synovioma, mesothelioma, Ewing's tumor, leiomyosarcoma, rhabdomyosarcoma, colon carcinoma, colorectal cancer, pancreatic cancer, breast cancer, ovarian cancer, prostate cancer, squamous cell carcinoma, basal cell carcinoma, adenocarcinoma, sweat gland carcinoma, sebaceous gland carcinoma, papillary carcinoma, papillary adenocarcinomas, cystadenocarcinoma, medullary carcinoma, bronchogenic carcinoma, renal cell carcinoma, hepatoma, bile duct carcinoma, liver cancer, choriocarcinoma, seminoma, embryonal carcinoma, Wilms' tumor, cervical cancer, bone cancer, brain tumor, testicular cancer, lung carcinoma, small cell lung carcinoma, bladder carcinoma, epithelial carcinoma, glioma, astrocytoma, medulloblastoma, craniopharyngioma, ependymoma, pinealoma, hemangioblastoma, acoustic neuroma, oligodendroglioma, meningioma, melanoma, neuroblastoma, retinoblastoma; leukemias, e.g., acute lymphocytic leukemia and acute myelocytic leukemia (myeloblastic, promyelocytic, myelomonocytic, monocytic and erythroleukemia); chronic leukemia (chronic myelocytic (granulocytic) leukemia and chronic lymphocytic leukemia); and polycythemia vera, lymphoma (Hodgkin's disease and non-Hodgkin's disease), myeloma, multiple myeloma, Waldenstrom's macroglobulinemia, and heavy chain disease. In some embodiments, cancers are epithlelial in nature and include but are not limited to, bladder cancer, breast cancer, cervical cancer, colon cancer, gynecologic cancers, renal cancer, laryngeal cancer, lung cancer, oral cancer, head and neck cancer, ovarian cancer, pancreatic cancer, prostate cancer, or skin cancer. In other embodiments, the cancer is breast cancer, prostate cancer, lung cancer, or colon cancer. In still other embodiments, the epithelial cancer is non-small-cell lung cancer, nonpapillary renal cell carcinoma, cervical carcinoma, ovarian carcinoma, or breast carcinoma. The epithelial cancers may be characterized in various other ways including, but not limited to, serous, endometrioid, mucinous, clear cell, Brenner, or undifferentiated. In some embodiments, the cancer comprises a solid tumor. In some embodiments, the tumor is an adenocarcinoma, an adrenal tumor, an anal tumor, a bile duct tumor, a bladder tumor, a bone tumor, a blood born tumor, a brain/CNS tumor, a breast tumor, a cervical tumor, a colorectal tumor, an endometrial tumor, an esophageal tumor, an Ewing tumor, an eye tumor, a gallbladder tumor, a gastrointestinal, a kidney tumor, a laryngeal or hypopharyngreal tumor, a liver tumor, a lung tumor, a mesothelioma tumor, a multiple myeloma tumor, a muscle tumor, a nasopharyngeal tumor, a neuroblastoma, an oral tumor, an osteosarcoma, an ovarian tumor, a pancreatic tumor, a penile tumor, a pituitary tumor, a primary tumor, a prostate tumor, a retinoblastoma, a Rhabdomyosarcoma, a salivary gland tumor, a soft tissue sarcoma, a melanoma, a metastatic tumor, a basal cell carcinoma, a Merkel cell tumor, a testicular tumor, a thymus tumor, a thyroid tumor, a uterine tumor, a vaginal tumor, a vulvar tumor, or a Wilms tumor. As used herein, the phrase “conjoint administration” refers to any form of administration of two or more different therapeutic agents such that the second agent is administered while the previously administered therapeutic agent is still effective in the body (e.g., the two agents are simultaneously effective in the subject, which may include synergistic effects of the two agents). For example, the different therapeutic agents can be administered either in the same formulation or in separate formulations, either concomitantly or sequentially. In certain embodiments, the different therapeutic agents can be administered within about one hour, about 12 hours, about 24 hours, about 36 hours, about 48 hours, about 72 hours, or about a week of one another. Thus, a subject who receives such treatment can benefit from a combined effect of different therapeutic agents. As used herein, any two agents and/or additional agents may be conjointly administered according to the methods provided herein. Interleukin 12 (IL-12) family is secreted by activated antigen presenting cells (APC) during antigen presentation to naïve T cells while IL-35 is a product of regulatory T and B cells. They provide the bridge between innate and adaptive immune systems by priming naïve CD4⁺ T cells to differentiate into cytokine-producing T-helper subsets and memory T cells. In addition to their influence on cell-fate decisions of differentiating lymphocytes, IL- 12 cytokines regulate cellular pathways required for proper functioning of the immune system, with some members activating pro-inflammatory responses that confer protection against infection while others restrain unbridled immune responses that cause autoimmune diseases. Exemplary nucleotide and amino acid sequences of IL-12 and IL-15, which correspond to NCBI Accession numbers, are listed below in Table 1 below. Table 1

SEQ ID NO: 11: Human IL-12B Gene NC_000005.10:c159330487-159314780 [GeneID=3593] [chromosome=5]

GCTAGTGGGAATACCTCAGCGTAAGTGGCCAGGAGATGCCAGGAATCTCCACTATTTCCCTTCCAGTGTG

CTAGCTTGTTGCCTTAGGAATATCTTAAAATAAGCTCAATGCCACCAAGCCTTCTTAAAGGGCTCCTTTC

Interleukin-15 is a protein that in humans is encoded by the IL15 gene. IL-15 binds to and signals through a complex composed of IL-2/IL-15 receptor beta chain and the common gamma chain. Mature human IL-15 is a 14–15 kDa glycoprotein and a member of the four α-helix bundle family of cytokines. In both humans and mice cellular IL-15 production appears to be under stringent control through regulation of transcription, translation, translocation, and intracellular trafficking. A variety of cell types constitutively express IL-15 mRNA, and these include monocytes, macrophages, DCs, keratinocytes, epidermal skin cells, fibroblasts, various epithelial cells, bone marrow stromal cells, and nerve cells. In addition, IL-15 mRNA is also expressed in kidney, placenta, lung, heart, skeletal muscle, and brain tissues. Exemplary nucleotide and amino acid sequences of human IL-15, which correspond to NCBI Accession numbers, are listed below in Table 2. Table 2:

Interferons (IFNs) are a family of proteins synthesized in mammalian cells in response to stimulation by viruses, mitogens, and other agents. Interferons have been shown to have antiviral, antiproliferative, and immunomodulatory activities. Over 20 distinct interferons have been identified in humans and they are classified as type I, type II, and type III interferons. INF-γ a soluble cytokine that is a member of the type II interferon class. The encoded protein is secreted by cells of both the innate and adaptive immune systems. The active protein is a homodimer that binds to the interferon gamma receptor which triggers a cellular response to viral and microbial infections. Exemplary nucleotide and amino acid sequences of human INF-γ, which correspond to NCBI Accession numbers, are listed below in Table 3. Table 3

It will be appreciated that specific sequence identifiers (SEQ ID NOs) have been referenced throughout the specification for purposes of illustration and should therefore not be construed to be limiting. Any marker encompassed by the present invention, including, but not limited to, the markers described in the specification and markers described herein, are well-known in the art and may be used in the embodiments encompassed by the present invention. INF-α is encoded by gene that is a member of the alpha interferon gene cluster on chromosome 9. The encoded cytokine is a member of the type I interferon family that is produced in response to viral infection as a key part of the innate immune response with potent antiviral, antiproliferative and immunomodulatory properties. This cytokine, like other type I interferons, binds a plasma membrane receptor made of IFNAR1 and IFNAR2 that is ubiquitously expressed, and thus is able to act on virtually all body cells. Exemplary nucleotide and amino acid sequences of human INF-α, which correspond to NCBI Accession numbers, are listed below in Table 4. Table 4

It will be appreciated that specific sequence identifiers (SEQ ID NOs) have been referenced throughout the specification for purposes of illustration and should therefore not be construed to be limiting. Any marker encompassed by the present invention, including, but not limited to, the markers described in the specification and markers described herein, are well-known in the art and may be used in the embodiments encompassed by the present invention. The phrase “pharmaceutically-acceptable carrier” as used herein means a pharmaceutically-acceptable material, composition or vehicle, such as a liquid or solid filler, diluent, excipient, or solvent encapsulating material, involved in carrying or transporting the subject compound from one organ, or portion of the body, to another organ, or portion of the body. The terms “polynucleotide”, and “nucleic acid” are used interchangeably. They refer to a polymeric form of nucleotides of any length, either deoxyribonucleotides or ribonucleotides, or analogs thereof. Polynucleotides may have any three-dimensional structure, and may perform any function, known or unknown. The following are non- limiting examples of polynucleotides: coding or non-coding regions of a gene or gene fragment, loci (locus) defined from linkage analysis, exons, introns, messenger RNA (mRNA), transfer RNA, ribosomal RNA, ribozymes, cDNA, recombinant polynucleotides, branched polynucleotides, plasmids, vectors, isolated DNA of any sequence, isolated RNA of any sequence, nucleic acid probes, and primers. A polynucleotide may comprise modified nucleotides, such as methylated nucleotides and nucleotide analogs. If present, modifications to the nucleotide structure may be imparted before or after assembly of the polymer. The sequence of nucleotides may be interrupted by non-nucleotide components. A polynucleotide may be further modified, such as by conjugation with a labeling component. The term “recombinant” polynucleotide means a polynucleotide of genomic, cDNA, semisynthetic, or synthetic origin which either does not occur in nature or is linked to another polynucleotide in a non-natural arrangement. The terms “prevent,” “preventing,” “prevention,” and the like refer to reducing the probability of developing a disease, disorder, or condition in a subject, who does not have, but is at risk of or susceptible to developing a disease, disorder, or condition. As used herein, the term “subject” means a human or non-human animal selected for treatment or therapy. The phrases "therapeutically-effective amount" and “effective amount” as used herein means the amount of an agent which is effective for producing the desired therapeutic effect in at least a sub-population of cells in a subject at a reasonable benefit/risk ratio applicable to any medical treatment. “Treating” a disease in a subject or “treating” a subject having a disease refers to subjecting the subject to a pharmaceutical treatment, e.g., the administration of a drug, such that at least one symptom of the disease is decreased or prevented from worsening. Gene Therapy In certain embodiments, provided herein are agents that are vectors that contain the isolated nucleic acid molecules described herein, such as those that encode an IL-12 peptide, an IL-15 peptide, or an interferon peptide. As used herein, the term “vector,” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a “plasmid”, which refers to a circular double stranded DNA loop into which additional DNA segments may be ligated. Another type of vector is a viral vector, wherein additional DNA segments may be ligated into the viral genome. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) can be integrated into the genome of a host cell upon introduction into the host cell, and thereby be replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes. Such vectors are referred to herein as “recombinant expression vectors” (or simply, “expression vectors”). In certain embodiments, provided herein are cells that contain a nucleic acid described herein (e.g., a nucleic acid encoding an antibody, antigen binding fragment thereof, antibody-like molecule, or polypeptide described herein). The cell can be, for example, prokaryotic, eukaryotic, mammalian, avian, murine and/or human. The nucleic acids described herein may be contacted with a cell or administered to an organism (e.g., a human). Alternatively, constructs and/or vectors encoding the interfering RNA molecules may be contacted with or introduced into a cell or organism. In certain embodiments, a viral, retroviral or lentiviral vector is used. In some embodiments, IL-15, IL-12, or interferon peptides disclosed herein are delivered to subjects by use of viral vectors. Viral vector systems which can be utilized with the methods and compositions described herein include, but are not limited to, (a) adenovirus vectors; (b) retrovirus vectors, including but not limited to lentiviral vectors, moloney murine leukemia virus, etc.; (c) adeno-associated virus vectors; (d) herpes simplex virus vectors; (e) SV 40 vectors; (f) polyoma virus vectors; (g) papilloma virus vectors; (h) picornavirus vectors; (i) pox virus vectors such as an orthopox, e.g., vaccinia virus vectors or avipox, e.g. canary pox or fowl pox; and (j) a helper-dependent or gutless adenovirus. In some embodiments, adenoviruses can be used to deliver nucleic acids encoding an interferon peptide. Adenoviruses have the advantage of being capable of infecting non- dividing cells. Kozarsky and Wilson, Current Opinion in Genetics and Development 3:499- 503 (1993) present a review of adenovirus-based gene therapy. The adeno-associated virus is a non-pathogenic parvovirus, consisting of a 4.7 kb single-stranded DNA genome, with no envelope icosahedral capsid. The genome contains three open reading frames (ORFs) flanked by inverted terminal repeats (ITRs) that function as a replication and packaging signal of viral origin. Rep ORF encodes four non-structural proteins that play a role in virus replication, transcriptional regulation, site-specific integration, and virion assembly. Cap ORF encodes three structural proteins (VP 1-3), which are assembled to form a 60-dimensional viral capsid. Finally, ORF, present as an alternative reading frame in the cap gene, produces assembly activating protein (AAP), a viral protein that localizes AAV capsid proteins into the nucleolus and functions during capsid assembly. There are several natural ("wild type") serotypes and more than 100 known AAV variants, each of which differs in amino acid sequence, especially in the hypervariable regions of capsid proteins, and thus in its gene delivery properties. No association has been found between any AAV and any human disease, which makes recombinant AAV attractive for clinical applications. For the purposes of the description herein, the term “AAV” is an abbreviation for adeno-associated virus, including, without limitation, the virus itself and its derivatives. Except where otherwise indicated, terminology refers to all subtypes or serotypes, and both replication-competent and recombinant forms. The term “AAV” includes, without limitation, AAV type 1 (AAV-1 or AAV1), AAV type 2 (AAV-2 or AAV2), AAV type 3A (AAV-3A or AAV3A), AAV type 3B (AAV-3B or AAV3B), AAV type 4 (AAV-4 or AAV4), AAV type 5 (AAV-5 or AAV5), AAV type 6 (AAV-6 or AAV6), AAV type 7 (AAV-7 or AAV7), type AAV 8 (AAV-8 or AAV8), AAV type 9 (AAV-9 or AAV9), AAV type 10 (AAV-10 or AAV10 or AAVrh10), avian AAV, bovine AAV, canine AAV, goat AAV, equine AAV, AAV primacy, AAV is not primate, and sheep AAV. “Primate AAV” refers to AAV that infects primates, “Primate AAV” refers to AAV that infects non- primate mammals, In some embodiments, a AAV vector that expresses a nucleic acid agent encoding a interferon peptide is a recombinant AAV vector having, for example, either an U6 or H1 RNA promoter, or a cytomegalovirus (CMV) promoter. Suitable AAV vectors for use in agents, compositions, and methods described include, but are not limited to AAVs described in Passini et al., Methods Mol. Biol.246: 225-36 (2004). Genomic sequences of various AAV serotypes, as well as sequences of native terminal repeats (TRs), Rep proteins and capsid subunits, are known in the art and included in the present disclosure. Such sequences can be found in the literature or in public databases such as GenBank. See, for example, GenBank access numbers NC_002077.1 (AAV1), AF063497.1 (AAV1), NC_001401.2 (AAV2), AF043303.1 (AAV2), J01901.1 (AAV2), U48704.1 (AAV3A), NC_001729.1 (AAV3A), AF028705.1 (AAV3B), NC_001829.1 (AAV4), U89790.1 (AAV4), NC_006152.1 (AA5), AF085716.1 (AAV-5), AF028704.1 (AAV6) , NC_006260.1 (AAV7), AF513851.1 (AAV7), AF513852.1 (AAV8) NC_006261.1 (AAV-8), AY530579.1 (AAV9), AAT46337 (AAV10) and AAO88208 (AAVrh10); the descriptions of which are incorporated herein by reference. See also, for example, Srivistava et al. (1983) J. Virology 45: 555; Chiorini et al. (1998) J. Virology 71: 6823; Chiorini et al. (1999) J. Virology 73: 1309; Bantel-Schaal et al. (1999) J. Virology 73: 939; Xiao et al. (1999) J. Virology 73: 3994; Muramatsu et al. (1996) Virology 221: 208; Shade et. et al. (1986) J. Virol.58: 921; Gao et al. (2002) Proc. Nat. Acad Sci. USA 99: 11854; Moris et al. (2004) Virology 33: 375-383; international patent publications WO 00/28061, WO 99/61601, WO 98/11244; and US Pat. US No.6156303. The sequences of naturally occurring cap (capsid) proteins associated with AAV serotypes are known in the art and include those described herein as AAV1, AAV2, AAV3A, AAV3B, AAV4, AAV5, AAV6, AAV7, AAV8, AAV9, AAV10 and AAVrh10. Also included herein are AAV variants for targeting cells and/or tissues of interest. The terms “AAV capsid protein variant” or “AAV variant” refer to an AAV capsid protein containing an amino acid sequence that includes at least one modification or substitution (including deletion, insertion, point mutation, etc.) compared to the sequence a naturally occurring, or wild-type AAV capsid protein sequence. An AAV capsid protein variant may have about 80% identity or more of the wild-type capsid protein amino acid sequence, for example 85% or more, 90% identity or more, or 95% identity or more for the wild-type capsid protein amino acid sequence, for example 98 % or 99% identity with wild-type capsid protein. The AAV capsid protein variant may be a non-wild type capsid protein. Also provided herein are AAV platforms that deliver a nucleic acid encoding at least one interferon peptide. Also included are solated nucleic acids comprising a nucleotide sequence that encodes an AAV capsid protein variant as described above. An isolated nucleic acid may be an AAV vector, for example, a recombinant AAV vector. For the purposes of the description of this document, the term "rAAV" is an abbreviation that refers to a recombinant adeno-associated virus. "Recombinant" as applied to a polynucleotide means that the polynucleotide is the product of various combinations of the cloning, restriction or ligation steps and other procedures that result in a construct different from the polynucleotide found in nature. A recombinant virus is a viral particle containing a recombinant polynucleotide. The terms respectively include replicates of the original polynucleotide construct and offspring of the original viral construct. The term “rAAV vector” embraces rAAV virions (ie, viral particles of rAAV) (e.g., an infectious rAAV virion), which by definition include an rAAV polynucleotide; and also encompasses polynucleotides encoding rAAV (e.g., a single-stranded polynucleotide encoding rAAV (sc-rAAV), a double-stranded polynucleotide encoding rAAV (dc-rAAV), for example, plasmids encoding rAAV; and the like). If the AAV virion contains a heterologous polynucleotide (i.e., a polynucleotide other than the wild-type AAV genome, for example, a transgene that must be delivered to the target cell), it is usually called the "recombinant AAV (rAAV) virion" or "viral particle rAAV". In general, a heterologous polynucleotide is flanked by at least one and, as a rule, two inverted AAV terminal repeat sequences (ITRs). In some embodiments of the rAAV vector embodiment described herein, a nucleotide sequence encoding a gene product of interest is operably linked to a constitutive promoter. Suitable constitutive promoters include, for example, the cytomegalovirus (CMV) promoter (Stinski et al. (1985) Journal of Virology 55 (2): 431-441), the chicken early β-actin (CBA) promoter promoter / rabbit β-globin intron (CAG) (Miyazaki et al. (1989) Gene 79 (2): 269-277, CB SB (Jacobson et al. (2006) Molecular Therapy 13 (6): 1074-1084), human elongation factor 1α promoter (EF1α ) (Kim et al. (1990) Gene 91 (2): 217-223), human phosphoglycerate kinase (PGK) promoter (Singer-Sam et al. (1984) Gene 32 (3): 409-417, heavy chain mitochondrial promoter (Loderio et al. (2012) PNAS 109 (17): 6513-6518), the ubiquitin promoter (Wulff et al. (1990) FEBS Letters 261: 101-105). In other embodiments, the nucleotide sequence encoding the protein of interest a gene product operably linked to an inducible promoter. In some cases, a nucleotide sequence encoding a gene product of interest is operably linked to a tissue specific a specific or cell- specific regulatory element. The term "auxiliary virus" for AAV refers to a virus that allows AAV (e.g., wild- type AAV) to replicate and pack using mammalian cells. Many such auxiliary viruses for AAV are known in the art, including adenoviruses, herpes viruses and poxviruses, such as smallpox. Adenoviruses cover a number of different subgroups, although type 5 adenovirus subgroup C is most commonly used. Numerous human, non-human, and avian adenoviruses are known and accessible from repositories such as ATCC. Herpes viruses include, for example, herpes simplex viruses (HSV) and Epstein-Barr viruses (EBV), as well as cytomegaloviruses (CMV) and Aujeszky's disease viruses (PRV); which are also available at depositories such as ATCC. Polypeptide Agents In some embodiments, the agent provided herein is a polypeptide agent (e.g., an unmodified or modified IL-12, IL-15 or interferon peptide). In some embodiments, the agent may be a chimeric or fusion interferon polypeptide. A fusion or chimeric polypeptide can be produced by standard recombinant DNA techniques. For example, DNA fragments coding for the different polypeptide sequences are ligated together in-frame in accordance with conventional techniques, for example by employing blunt-ended or stagger-ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment, the fusion gene can be synthesized by conventional techniques including automated DNA synthesizers. Alternatively, PCR amplification of gene fragments can be carried out using anchor primers which give rise to complementary overhangs between two consecutive gene fragments which can subsequently be annealed and re-amplified to generate a chimeric gene sequence (see, for example, Current Protocols in Molecular Biology, Ausubel et al., eds., John Wiley & Sons: 1992). Moreover, many expression vectors are commercially available that already encode a fusion moiety. The polypeptides described herein can be produced in prokaryotic or eukaryotic host cells by expression of polynucleotides encoding a polypeptide(s). Alternatively, such peptides can be synthesized by chemical methods. Methods for expression of heterologous polypeptides in recombinant hosts, chemical synthesis of polypeptides, and in vitro translation are well known in the art and are described further in Maniatis et al., Molecular Cloning: A Laboratory Manual (1989), 2nd Ed., Cold Spring Harbor, N. Y.; Berger and Kimmel, Methods in Enzymology, Volume 152, Guide to Molecular Cloning Techniques (1987), Academic Press, Inc., San Diego, Calif.; Merrifield, J. (1969) J. Am. Chem. Soc. 91:501; Chaiken I. M. (1981) CRC Crit. Rev. Biochem.11:255; Kaiser et al. (1989) Science 243:187; Merrifield, B. (1986) Science 232:342; Kent, S. B. H. (1988) Annu. Rev. Biochem.57:957; and Offord, R. E. (1980) Semisynthetic Proteins, Wiley Publishing, which are incorporated herein by reference. Pharmaceutical Compositions In certain embodiments, provided herein is a composition, e.g., a pharmaceutical composition, containing a viral vector encoding at least one IL-12, IL-15 or interferon peptide described herein together with a pharmaceutically acceptable carrier. In one embodiment, the composition includes a combination of multiple agents (e.g., two or more viral vectors) described herein. In certain embodiments, provided herein is a composition, e.g., a pharmaceutical composition, containing at least one peptide disclosed herein together with a pharmaceutically acceptable carrier. In one embodiment, the composition includes a combination of multiple (e.g., two or more) agents described herein. In some embodiments, the pharmaceutical composition is delivered locally or systemically. In some embodiments, the pharmaceutical composition may be administered to a tumor present in the subject. In some embodiments, the agent or pharmaceutical composition is administered with an additional cancer therapeutic agent. In some embodiments, the additional cancer therapeutic agent is a chemotherapeutic agent. In some embodiments, the pharmaceutical composition further comprises an additional agent for treatment of cancer. In some embodiments, the additional agent is a tumor vaccine. In certain embodiments, the additional therapeutic agent is a chemotherapeutic agents include alkylating agents such as thiotepa and cyclophosphamide (Cytoxan™); alkyl sulfonates such as busulfan, improsulfan and piposulfan; aziridines such as benzodopa, carboquone, meturedopa, and uredopa; emylerumines and memylamelamines including alfretamine, triemylenemelamine, triethylenephosphoramide, triethylenethiophosphoramide, and trimemylolomelamine; acetogenins (especially bullatacin and bullatacinone); a camptothecin (including synthetic analogue topotecan); bryostatin; callystatin; CC-1065 (including its adozelesin, carzelesin and bizelesin synthetic analogues); cryptophycins (articularly cryptophycin 1 and cryptophycin 8); dolastatin; duocarmycin (including the synthetic analogues, KW-2189 and CBI-TMI); eleutherobin; pancratistatin; a sarcodictyin; spongistatin; nitrogen mustards such as chlorambucil, chlornaphazine, cholophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamide, uracil mustard; nitrosoureas such as carmustine, chlorozotocin, foremustine, lomustine, nimustine, ranimustine; antibiotics such as the enediyne antibiotics (e.g., calicheamicin, especially calicheamicin gammall and calicheamicin phili); dynemicin, including dynemicin A; bisphosphonates, such as clodronate; an esperamicin; as well as neocarzinostatin chromophore and related chromoprotein enediyne antibiotic chromomophores), aclacinomysins, actinomycin, authramycin, azaserine, bleomycins, cactinomycin, carabicin, carrninomycin, carzinophilin, chromomycins, dactinomycin, daunorubicin, detorubicin, 6- diazo-5-oxo-L-norleucine, doxorubicin (Adramycin™) (including morpholino-doxorubicin, cyanomorpholino-doxorubicin, 2-pyrrolino-doxorubicin and deoxydoxorubicin), epirubicin, esorubicin, idarubicin, marcellomycin, mitomycins such as mitomycin C, mycophenolic acid, nogalamycin, olivomycins, peplomycin, potfiromycin, puromycin, quelamycin, rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, zorubicin; anti- metabolites such as methotrexate and 5-fluorouracil (5-FU); folic acid analogues such as demopterin, methotrexate, pteropterin, trimetrexate; purine analogs such as fludarabine, 6- mercaptopurine, thiamiprine, thioguanine; pyrimidine analogues such as ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine; androgens such as calusterone, dromostanolone propionate, epitiostanol, mepitiostane, testolactone; anti-adrenals such as aminoglutethimide, mitotane, trilostane; folic acid replinisher such as frolinic acid; aceglatone; aldophosphamide glycoside; aminolevulinic acid; eniluracil; amsacrine; hestrabucil; bisantrene; edatraxate; defofamine; demecolcine; diaziquone; elformthine; elliptinium acetate; an epothilone; etoglucid; gallium nitrate; hydroxyurea; lentinan; lonidamine; maytansinoids such as maytansine and ansamitocins; mitoguazone; mitoxantrone; mopidamol; nitracrine; pentostatin; phenamet; pirarubicin; losoxantrone; podophyllinic acid; 2-ethylhydrazide; procarbazine; PSK™; razoxane; rhizoxin; sizofiran; spirogermanium; tenuazonic acid; triaziquone; 2,2',2''- tricUorotriemylamine; trichothecenes (especially T-2 toxin, verracurin A, roridin A and anguidine); urethane; vindesine; dacarbazine; mannomustine; mitobronitol; mitolactol; pipobroman; gacytosine; arabinoside ("Ara-C"); cyclophosphamide; thiopeta; taxoids, e.g., paclitaxel (Taxol™, Bristol Meyers Squibb Oncology, Princeton, N.J.) and docetaxel (Taxoteret™, Rhone-Poulenc Rorer, Antony, France); chlorambucil; gemcitabine (Gemzar™); 6-thioguanine; mercaptopurine; methotrexate; platinum analogs such as cisplatin and carboplatin; vinblastine; platinum; etoposide (VP-16); ifosfamide; mitroxantrone; vancristine; vinorelbine (Navelbine™); novantrone; teniposide; edatrexate; daunomycin; aminopterin; xeoloda; ibandronate; CPT-11; topoisomerase inhibitor RFS 2000; difluoromethylornithine (DMFO); retinoids such as retinoic acid; capecitabine; and pharmaceutically acceptable salts, acids or derivatives of any of the above. Also included in the definition of “chemotherapeutic agent” are anti-hormonal agents that act to regulate or inhibit hormone action on tumors such as anti-estrogens and selective estrogen receptor modulators (SERMs), including, for example, tamoxifen (including Nolvadex™), raloxifene, droloxifene, 4-hydroxytamoxifen, trioxifene, keoxifene, LY117018, onapristone, and toremifene (Fareston™); inhibitors of the enzyme aromatase, which regulates estrogen production in the adrenal glands, such as, for example, 4(5)-imidazoles, aminoglutethimide, megestrol acetate (Megace™), exemestane, formestane, fadrozole, vorozole (Rivisor™), letrozole (Femara™), and anastrozole (Arimidex™); and anti- androgens such as flutamide, nilutamide, bicalutamide, leuprohde, and goserelin; and pharmaceutically acceptable salts, acids or derivatives of any of the above. In some embodiments, the additional cancer therapeutic agent is an immune checkpoint inhibitor. Immune Checkpoint inhibition broadly refers to inhibiting the checkpoints that cancer cells can produce to prevent or downregulate an immune response. Examples of immune checkpoint proteins are CTLA-4, PD-1, VISTA, B7-H2, B7-H3, PD-L1, B7-H4, B7-H6, ICOS, HVEM, PD-L2, CD160, gp49B, PIR-B, KIR family receptors, TIM-1, TIM-3, TIM- 4, LAG-3, BTLA, SIRPalpha (CD47), CD48, 2B4 (CD244), B7.1, B7.2, ILT-2, ILT-4, TIGIT, HHLA2, butyrophilins, A2aR, and combinations thereof. The pharmaceutical compositions and/or agents disclosed herein may be specially formulated for administration in solid or liquid form, including those adapted for the following: (1) intrathecal administration; (2) oral administration, for example, drenches (aqueous or non-aqueous solutions or suspensions), tablets, e.g., those targeted for buccal, sublingual, and systemic absorption, boluses, powders, granules, pastes for application to the tongue; or (3) parenteral administration, for example, by subcutaneous, intramuscular, intravenous, intrathecal, intracerebral or epidural injection as, for example, a sterile solution or suspension, or sustained-release formulation. Methods of preparing pharmaceutical formulations or compositions include the step of bringing into association an agent described herein with the carrier and, optionally, one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing into association an agent described herein with liquid carriers, or finely divided solid carriers, or both, and then, if necessary, shaping the product. Pharmaceutical compositions suitable for parenteral administration comprise one or more agents described herein in combination with one or more pharmaceutically-acceptable sterile isotonic aqueous or nonaqueous solutions, dispersions, suspensions or emulsions, or sterile powders which may be reconstituted into sterile injectable solutions or dispersions just prior to use, which may contain sugars, alcohols, antioxidants, buffers, bacteriostats, solutes which render the formulation isotonic with the blood of the intended recipient or suspending or thickening agents. Examples of suitable aqueous and nonaqueous carriers which may be employed in the pharmaceutical compositions include water, ethanol, dimethyl sulfoxide (DMSO), polyols (such as glycerol, propylene glycol, polyethylene glycol, and the like), and suitable mixtures thereof, vegetable oils, such as olive oil, and injectable organic esters, such as ethyl oleate. Proper fluidity can be maintained, for example, by the use of coating materials, such as lecithin, by the maintenance of the required particle size in the case of dispersions, and by the use of surfactants. Therapeutic Methods In some aspects, provided herein are methods and compositions of treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for at least one interferon peptide. In some aspects, provided herein are methods and compositions for treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject at least one interferon peptide. In some embodiments, the cancer includes a solid tumor. “Cancers” further include, but are not limited to, cancer cells from the bladder, blood, bone, bone marrow, brain, breast, colon, esophagus, gastrointestine, gum, head, kidney, liver, lung, nasopharynx, neck, ovary, prostate, skin, stomach, testis, tongue, or uterus. In addition, the cancer may specifically be of the following histological type, though it is not limited to these: neoplasm, malignant; carcinoma; carcinoma, undifferentiated; giant and spindle cell carcinoma; small cell carcinoma; papillary carcinoma; squamous cell carcinoma; lymphoepithelial carcinoma; basal cell carcinoma; pilomatrix carcinoma; transitional cell carcinoma; papillary transitional cell carcinoma; adenocarcinoma; gastrinoma, malignant; cholangiocarcinoma; hepatocellular carcinoma; combined hepatocellular carcinoma and cholangiocarcinoma; trabecular adenocarcinoma; adenoid cystic carcinoma; adenocarcinoma in adenomatous polyp; adenocarcinoma, familial polyposis coli; solid carcinoma; carcinoid tumor, malignant; branchiolo-alveolar adenocarcinoma; papillary adenocarcinoma; chromophobe carcinoma; acidophil carcinoma; oxyphilic adenocarcinoma; basophil carcinoma; clear cell adenocarcinoma; granular cell carcinoma; follicular adenocarcinoma; papillary and follicular adenocarcinoma; nonencapsulating sclerosing carcinoma; adrenal cortical carcinoma; endometrioid carcinoma; skin appendage carcinoma; apocrine adenocarcinoma; sebaceous adenocarcinoma; ceruminous adenocarcinoma; mucoepidermoid carcinoma; cystadenocarcinoma; papillary cystadenocarcinoma; papillary serous cystadenocarcinoma; mucinous cystadenocarcinoma; mucinous adenocarcinoma; signet ring cell carcinoma; infiltrating duct carcinoma; medullary carcinoma; lobular carcinoma; inflammatory carcinoma; mammary paget's disease; acinar cell carcinoma; adenosquamous carcinoma; adenocarcinoma w/squamous metaplasia; malignant thymoma; malignant ovarian stromal tumor; malignant thecoma; malignant granulosa cell tumor; and malignant roblastoma; sertoli cell carcinoma; malignant leydig cell tumor; malignant lipid cell tumor; malignant paraganglioma; malignant extra-mammary paraganglioma; pheochromocytoma; glomangiosarcoma; malignant melanoma; amelanotic melanoma; superficial spreading melanoma; malignant melanoma in giant pigmented nevus; epithelioid cell melanoma; malignant blue nevus; sarcoma; fibrosarcoma; malignant fibrous histiocytoma; myxosarcoma; liposarcoma; leiomyosarcoma; rhabdomyosarcoma; embryonal rhabdomyosarcoma; alveolar rhabdomyosarcoma; stromal sarcoma; malignant mixed tumor; mullerian mixed tumor; nephroblastoma; hepatoblastoma; carcinosarcoma; malignant mesenchymoma; malignant brenner tumor; malignant phyllodes tumor; synovial sarcoma; malignant mesothelioma; dysgerminoma; embryonal carcinoma; malignant teratoma; malignant struma ovarii; choriocarcinoma; malignant mesonephroma; hemangiosarcoma; malignant hemangioendothelioma; kaposi's sarcoma; malignant hemangiopericytoma; lymphangiosarcoma; osteosarcoma; juxtacortical osteosarcoma; chondrosarcoma; malignant chondroblastoma; mesenchymal chondrosarcoma; giant cell tumor of bone; ewing's sarcoma; malignant odontogenic tumor; ameloblastic odontosarcoma; malignant ameloblastoma; ameloblastic fibrosarcoma; malignant pinealoma; chordoma; malignant glioma; ependymoma; astrocytoma; protoplasmic astrocytoma; fibrillary astrocytoma; astroblastoma; glioblastoma; oligodendroglioma; oligodendroblastoma; primitive neuroectodermal; cerebellar sarcoma; ganglioneuroblastoma; neuroblastoma; retinoblastoma; olfactory neurogenic tumor; malignant meningioma; neurofibrosarcoma; malignant neurilemmoma; malignant granular cell tumor; malignant lymphoma; Hodgkin's disease; Hodgkin's lymphoma; paragranuloma; small lymphocytic malignant lymphoma; diffuse large cell malignant lymphoma; follicular malignant lymphoma; mycosis fungoides; other specified non-Hodgkin's lymphomas; malignant histiocytosis; multiple myeloma; mast cell sarcoma; immunoproliferative small intestinal disease; leukemia; lymphoid leukemia; plasma cell leukemia; erythroleukemia; lymphosarcoma cell leukemia; myeloid leukemia; basophilic leukemia; eosinophilic leukemia; monocytic leukemia; mast cell leukemia; megakaryoblastic leukemia; myeloid sarcoma; and hairy cell leukemia. In some embodiments, the cancer comprises a solid tumor including but not limited to an adenocarcinoma, an adrenal tumor, an anal tumor, a bile duct tumor, a bladder tumor, a bone tumor, a blood born tumor, a brain/CNS tumor, a breast tumor, a cervical tumor, a colorectal tumor, an endometrial tumor, an esophageal tumor, an Ewing tumor, an eye tumor, a gallbladder tumor, a gastrointestinal, a kidney tumor, a laryngeal or hypopharyngreal tumor, a liver tumor, a lung tumor, a mesothelioma tumor, a multiple myeloma tumor, a muscle tumor, a nasopharyngeal tumor, a neuroblastoma, an oral tumor, an osteosarcoma, an ovarian tumor, a pancreatic tumor, a penile tumor, a pituitary tumor, a primary tumor, a prostate tumor, a retinoblastoma, a Rhabdomyosarcoma, a salivary gland tumor, a soft tissue sarcoma, a melanoma (such as uveal melanoma (UVM), a metastatic tumor, a basal cell carcinoma, a Merkel cell tumor, a testicular tumor, a thymus tumor, a thyroid tumor, a uterine tumor, a vaginal tumor, a vulvar tumor, or a Wilms tumor. Actual dosage levels of the active ingredients in the pharmaceutical compositions or agents to be administered may be varied so as to obtain an amount of the active ingredient (e.g., an agent described herein) which is effective to achieve the desired therapeutic response for a particular patient, composition, and mode of administration, without being toxic to the patient. The compositions disclosed herein may be administered over any period of time effective to achieve the desired therapeutic response for a particular patient, composition, and mode of administration, without being toxic to the patient. The period of time may be at least 1 day, at least 10 days, at least 20 days, at least 30, days, at least 60 days, at least three months, at least six months, at least a year, at least three years, at least five years, or at least ten years. The dose may be administered when needed, sporadically, or at regular intervals. For example, the dose may be administered monthly, weekly, biweekly, triweekly, once a day, or twice a day. In certain embodiments, a dose of the composition is administered at regular intervals over a period of time. In some embodiments, a dose of the composition is administered at least once a week. In some embodiments, a dose of the composition is administered at least twice a week. In certain embodiments, a dose of the composition is administered at least three times a week. In some embodiments, a dose of the composition is administered at least once a day. In some embodiments, a dose of the composition is administered at least twice a day. In some embodiments, doses of the composition are administered for at least 1 week, for at least 2 weeks, for at least 3 weeks, for at least 4 weeks, for at least 1 month, for at least 2 months, for at least 3 months, for at least 4 months, for at least 5 months, for at least 6 months, for at least 1 year, for at least two years, at least three years, or at least five years. The selected dosage level will depend upon a variety of factors including the activity of the particular agent employed, the route of administration, the time of administration, the rate of excretion or metabolism of the particular compound being employed, the duration of the treatment, other drugs, compounds and/or materials used in combination with the particular compound employed, the age, sex, weight, condition, general health and prior medical history of the patient being treated, and like factors well known in the medical arts. A physician having ordinary skill in the art can readily determine and prescribe the effective amount of the pharmaceutical composition required. For example, the physician could prescribe and/or administer doses of the compounds employed in the pharmaceutical composition at levels lower than that required in order to achieve the desired therapeutic effect and gradually increase the dosage until the desired effect is achieved. Exemplification Example 1: Targeted AAV System to Control Cancer Cell Growth Metastasis to the cerebrospinal fluid (CSF)-filled leptomeninges, or leptomeningeal metastasis (LM), represents a fatal complication of cancer. Proteomic and transcriptomic analyses of human CSF reveal a substantial inflammatory infiltrate in LM. Here, it is shown that the solute and immune composition of CSF in the setting of LM changes dramatically, with notable enrichment in IFN-γ signaling. To investigate the mechanistic relationships between immune cell signaling and cancer cells within the leptomeninges, Applicant developed syngeneic lung, breast, and melanoma LM mouse models. Here, it is shown that transgenic host mice, lacking IFN-γ or its receptor, fail to control LM growth. Overexpression of Ifng through a targeted AAV system controls cancer cell growth independent of adaptive immunity. Leptomeningeal IFN-γ actively recruits and activates peripheral myeloid cells, generating a diverse spectrum of dendritic cell subsets. These migratory, CCR7+ dendritic cells orchestrate the influx, proliferation, and cytotoxic action of natural killer cells to control cancer cell growth in the leptomeninges. This work uncovers leptomeningeal-specific IFN-γ signaling and shows a novel immune-therapeutic approach against tumors. Introduction Metastasis, or spread of cancer to distant anatomic sites, requires cancer cells to enter into and thrive within microenvironments unlike those of the primary tumor. In parallel, immune cells migrate throughout the organism and enter these same microenvironments as a counter-offensive, carrying out complex cellular tasks to control the growth of disseminated malignant cells. This balance may tip in favor of cancer cell growth for a variety of reasons, most simply when immune cells are excluded, as is the case for the majority of metastases to the central nervous system. An important exception to this rule is that of leptomeningeal metastasis (LM). The leptomeninges, the cerebrospinal fluid (CSF)-filled protective coverings, encase the central nervous system. Cancer cell entry into the leptomeningeal space, or LM, provokes a profound inflammatory response, clinically reminiscent of infectious meningitis. Despite this abundance of immune cells and intense inflammatory signals, leptomeningeal cancer cells persist and even thrive, a reflection of inflammation-mediated transcriptional changes within these cancer cells. How and why these abundant infiltrating inflammatory cells fail to control cancer cell growth remains enigmatic. Non-canonical transcriptional and functional changes occur in macrophages in the setting of metastasis, suggesting that other immune cells within this anatomical compartment may also behave atypically. In addition, levels of inflammatory cytokines in the leptomeningeal space do not reflect those outside the leptomeninges, consistent with both intrathecal cytokine generation and alternative regulatory system(s) within this space. Formal investigations of this complex, anatomically site-specific, call-and-response between immune cells and cancer cells have remained incomplete, due to the lack of immunocompetent mouse models and to piecemeal computational approaches that do not encompass the entirety of cellular and humoral signaling within this under-appreciated anatomic space. To uncover the mechanisms whereby the immune system fails to control cancer cell growth in the leptomeningeal space, Applicant comprehensively captured and molecularly dissected the immune response to LM in human disease and novel immunocompetent mouse models at both the cellular and humoral levels. Results Leptomeningeal metastasis generates an inflamed milieu LM is a uniformly fatal neurologic consequence of cancer. Although any malignancy can result in LM, it most commonly results from breast, lung and melanoma primaries. Cancer cells enter into the leptomeningeal space accompanied by a host of leukocytes, as can be appreciated by classical techniques including CSF cytospins (Fig.1A). To understand this leukocytic pleocytosis at a molecular level, CSF was collected from breast and lung cancer patients with (n = 5) and without (n = 3) LM using the 10X platform, collecting single cell transcriptomes, assigning cell identity by clustering and marker gene expression (Fig.1B and Fig.7). In the absence of LM, the CSF is nearly acellular and contains predominantly CD4+ T cells (Fig.1A to 1C, and Fig.7). Pathological processes that do not directly involve the leptomeninges, such as parenchymal or dural metastases, remodel the CSF cell landscape towards reactive myeloid cells (Fig.7D to 7F). CSF from patients harboring LM was pleocytic and contained cells from a spectrum of lymphoid and myeloid lineages. To assess the molecular hallmarks of CSF pleocytosis and capture cell- to-cell communication, CSF from patients with breast cancer, lung cancer, and melanoma primaries, with and without LM, was subjected to targeted proteomic analysis by proximity extension assay (Fig.8A to 8C). In the presence of LM, CSF demonstrated a robust influx of soluble inflammatory ligands; 15 of these molecules were shared across the three tumor types (Fig.8D). Extending this cohort to include patients with a wide variety of solid tumor primaries confirmed elevated CSF levels of IFN-γ in the presence of LM (Fig.1D). Moreover, elevated CSF IFN-γ levels at diagnosis were associated with improved overall survival (Fig.1E). IFN-γ is well-known to exhibit both pro-tumorigenic and tumor- suppressive actions in a context-dependent manner; the presence of inflammatory and anti- inflammatory signals in cancer-infiltrated leptomeninges suggested a dense signaling network not clearly consistent with monotone behavior and canonical pathways. Formal identification of downstream leptomeningeal effectors of IFN-γ and the functional consequence(s) of their activation was investigated. Interferon-γ regulates leptomeningeal metastatic growth To enable these mechanistic studies, an iterative in vivo selection to generate six immunocompetent mouse LeptoM lines on two genetic backgrounds was investigated (Fig. 9A). These cell lines, subpopulations of the founding parental line, are phenotypically and transcriptomically distinct from their parental or brain parenchyma-tropic counterparts (Fig. 9B to 9M). Moreover, these LeptoM models faithfully recapitulate key histological and oncological features of human LM including CSF pleocytosis (Fig.2A) and brisk pace of illness (Fig.9B to 9M). To capture the complexity of leptomeningeal immune infiltrate at systems level, proteogenomic analysis of mouse leptomeningeal immune infiltrate was performed with 198 barcoded antibodies targeting cell surface epitopes and non-targeting isotype controls, coupled with single cell RNA-sequencing on the 10X platform; single-cell CITE-seq. This approach enables granular identification of immune cell subtypes and their origin. The mouse models mimic human CSF cellular composition in the setting of LM: a dramatic influx of leukocytes is observed, evenly split between myeloid and lymphoid populations (Fig.2B and 2C, and Fig.10, compare Fig.1B and 1C, and Fig.7E). In both human and mouse LM, the myeloid compartment is populated by monocyte-macrophages, and to a lesser extent, dendritic cells (DCs) (Fig.7E, and Fig.104). In the absence of LM, normal human CSF is T-cell predominant, whereas disease-free mouse leptomeninges are populated by B cells and neutrophils. Despite species-specific differences in the in the absence of malignancy, the presence of LM drives the CSF cellular composition to a common, myeloid-dominant pleocytosis, independent of vertebrate host. In light of this myeloid predominance, leptomeningeal IFN-γ signaling was investigated. Elevated levels of IFN-γ in mouse LM was detected, compared to vehicle- injected animals (Fig.2D), analogous to human disease (Fig.1D). To identify its source, CSF collected from mice with and without LM was subjected to flow cytometric assessment of IFN-γ production (Fig.11A). It was found that leptomeningeal T and NK cells produce IFN-γ. In parallel, human and mouse single-cell atlases were queried for IFNG transcript. In both mouse and human leptomeninges, T cells and NK cells produce IFN-γ (Fig.11B). Because IFN-γ binding to its cognate receptors triggers a signaling cascade that results in phosphorylation of STAT1 (pSTAT1), the levels of pSTAT1 in leptomeningeal immune infiltrates were assessed by flow cytometry. Increased levels of pSTAT1 were detected in mouse leptomeningeal dendritic cells, monocyte-macrophages, and T cells, but not natural killer (NK) cells (Fig.11C). Taken together, these results support a model whereby leptomeningeal monocyte-macrophages, dendritic cells and T cells respond to IFN-γ generated by leptomeningeal T and NK cells. To assess the contributions of IFN-γ signaling to leptomeningeal cancer growth, transgenic host mice lacking either the sole type II Interferon ligand, Ifng, or its receptor, Ifngr1, were leveraged, resulting in whole-body impairment of IFN-γ signaling. In both transgenic hosts and the three tested LM models, interruption of IFN-γ signaling led to uncontrolled cancer cell growth in the leptomeninges (Fig.2E and 2F). This effect was not observed when these LeptoM cells were orthotopically implanted in their primary sites or the subcutaneous tissues (Fig.13), consistent with a leptomeningeal-specific role for IFN-γ. In a context-dependent fashion, IFN-γ may either promote or inhibit cancer growth. This can be the result of direct IFN-γ signal to the cancer cell, or indirect signaling to the tumor microenvironment. To investigate whether IFN-γ acts directly on cancer cells and suppresses their growth in vivo, IFN-γ signaling in cancer cells was genetically abrogated by knocking out the Ifngr2 subunit of IFN-γ receptor with CRISPR/Cas9. Unlike control clones, these knock-out lines were unable to propagate IFN-γ response that normally leads to upregulation of MHC class I on the cell surface (Fig.41A to 41C). The lack of Ifngr2 in these cells did not alter their growth in vitro (Fig.41D to 41F), or in vivo (Fig.41G to 41I). Cancer-intrinsic IFN-γ signaling is thus not required for cancer cell survival in the leptomeninges. Therefore, IFN-γ mediates leptomeningeal cancer cell growth through indirect effects on the microenvironment. Because knockout of host IFN-γ promoted cancer cell growth, a complementary add-back strategy with weekly intra-cisternal introduction of recombinant mouse IFN-γ was pursued. While LeptoM cancer cells demonstrate capacity to receive IFN-γ signals (Fig.42A to 42D), this does not significantly impact their proliferation in vitro (Fig.42D to 42F). However, in vivo, addition of IFN-γ suppressed cancer cell growth within the leptomeninges (Fig.42G to 42J). Thus, IFN-γ suppressed intrathecal cancer cell growth in an indirect fashion, suggesting an interplay between IFN-γ and other cells in this inflammatory microenvironment. Leptomeningeal interferon-γ tumor suppression is independent of antigen presentation To uncover the downstream IFN-γ effectors in the context of LM, an experimental system enabling manipulation of CSF composition without frequent anesthesia or injection of foreign agents into the leptomeninges was designed. An adeno-associated viral (AAV)- based expression system was constructed to induce expression of exogenous Ifng or a control gene, Egfp, specifically in the mouse leptomeninges, (Fig.14A to 14B). With this technique, overexpressed leptomeningeal IFN-γ resulted in dramatic control of leptomeningeal metastatic cancer cell growth in all six syngeneic LeptoM models; overexpressed EGFP did not (Fig.3A to 3F, and Fig.14C to 14H). Importantly, this overexpression system did not result in neurodegeneration or neuroinflammation, as in the case of Type I Interferons. Indeed, a normal profile of astrocytes lining the ventricular space was observed, without apparent activation of parenchymal microglia, depletion of neural progenitors, change in neuronal tract distribution, or change in mature cortical neuron numbers (Fig.15). Similar to earlier reports, a decrease in the immature oligodendrocyte population in corpus callosum is detected. This was not reflected in cortical and subcortical layers where only a minor decrease in differentiated, CNPase- positive cortical and subcortical oligodendrocytes was shown (Fig.16). With this tool in hand, the key cell population(s) responsible for IFN-γ-dependent cancer control in the leptomeninges can be identified. The anti-cancer effect of IFN-γ was diminished when this IFN-γ overexpression system was established in fully immunodeficient NSG mice, confirming that immune cells mediate IFN-γ’s anti-cancer activity in the leptomeninges (Fig.3G, and Fig.17A to 17C). IFN-γ positively regulates antigen presentation. It was therefore surprising to observe the IFN-γ anti-tumor effect was preserved in Rag1-deficient animals with impaired adaptive immune system, indicating that IFN-γ’s anti-tumor function is independent of antigen presentation in the leptomeninges (Fig.3H, and Fig.17D to 17F). Iba1+ monocytes and macrophages are well-known IFN-γ effectors. Overexpression of Ifng resulted in accumulation of Iba1+ myeloid cells in the choroid plexus (Fig.3I), a structure that acts as an interface between the periphery and the leptomeninges, produces the majority of CSF, and serves as a gateway for immune cell entry. In this system, neither antibody-based, nor chemical depletion of monocyte- macrophage population resulted in impaired tumor growth control by IFN-γ (Fig.3J, and Fig.17G and 17H). IFN-γ-mediated leptomeningeal tumor control is thus dependent on the immune system, but independent of an antigen presentation, adaptive immunity, and monocyte-macrophage function. Dendritic cells orchestrate innate anti-tumor immune response in the leptomeninges Conventional DCs (cDC) are a professional phagocytic myeloid immune cell lineage that can propagate IFN-γ response. Their function in an antigen-independent setting is, however, less explored. To specifically deplete the cDC lineage in the mouse and clarify their role in LM, a transgenic line that expresses human diphtheria toxin receptor (DTR) under the control of endogenous mouse Zbtb46 was used. Within the hematopoietic compartment the ZBTB46 expression is restricted specifically to cDC progenitors, it is also expressed by other body cell types, such as endothelium. To avoid consequences related to systemic depletion of ZBTB46-expressing cells, bone marrow chimeras were generated. Lethally irradiated wild-type recipient mice were infused with bone marrow from wild-type or ZBTB46-DTR animals. In this scenario, diphtheria toxin (DTx) eliminates ZBTB46- expressing cDC progenitors (Fig.18), while retaining the normal function of other, non- hematopoietic cell types. After reconstitution of normal bone marrow function, leptomeningeal Ifng or Egfp was overexpressed, and introduced cancer cells. Introduction of DTx into wild-type chimera hosts did not alter the activity of IFN-γ; mice with ablated cDC demonstrated reduced IFN-γ-dependent tumor control (Fig.4A). These experiments suggested that leptomeningeal DCs, responding to IFN-γ (Fig.11C), mediate its anti-tumor action. To capture the complexity of the IFN-γ response in the leptomeningeal space at a systems level, leptomeningeal cells from Egfp- and Ifng-overexpressing mice were isolated in the presence and absence of LM, and profiled these cells with CITE-seq (Fig.19; total n = 24 mice from 4 conditions). The presence of all classical DC populations: cDCs1 and cDCs2, migratory CCR7+ DCs, and plasmacytoid DCs was confirmed (pDCs; Fig.4B and 4C). Molecular profiling of DCs isolated from Egfp- and Ifng-overexpressing mice revealed striking similarities between mouse and human leptomeningeal DCs (Fig.20), as well as site-specific (leptomeningeal) imprinted expression patterns different from those observed within extracranial sites. In the presence of cancer, or after IFN-γ induction, cDC populations accumulate within the leptomeninges (Fig.21A to 21C). To address IFN-γ- dependent relationships between these cDC populations, a proteogenomic atlas was queried. Outside of the CNS, CCR7+ DCs can arise from both cDC1 and cDC2 populations. The majority of leptomeningeal CCR7+ DCs, however, retained of the cDC2 surface expression profile, as detected with CITE-seq (Fig.21D and 21E). Given the leptomeningeal-specific expression pattern, this was approached computationally and first employed CellRank to predict terminal cell states, without the need to indicate the initial cell (Fig.21F). This analysis identified cDC2 cells as the major contributors to the leptomeningeal CCR7+ DC pool; it also identified CCR7+ DCs as predominantly a product of cDC2 maturation (Fig.21G and 21H). Trajectory analyses with Palantir was reproduced, modeling the cDC2-CCR7+ DC maturation axis (Fig.21I and 21J). Enrichment of IFN-γ- associated genes as cells transition to CCR7+ DCs was detected, consistent with IFN-γ contribution to CCR7+DC maturation from cDC2 cells (Fig.4D). Because the anti-tumor effect of leptomeningeal IFN-γ does not rely on antigen presentation, other anti-tumor pathways including cancer cell proliferation and death was examined. Prediction of cell cycling in transcriptomic cancer cell data revealed that cancer cells isolated from Ifng- overexpressing mice did not show defective proliferation (Fig.4E and 4F, and Fig.22A to 22C). However, immunofluorescence of cancer cells in the leptomeninges identified elevated caspase expression in the Ifng-overexpressing animals, consistent with apoptotic cell death (Fig.4G and Fig.22D to 22F). These results suggested that a cytotoxic immune population, supported by cDCs, restricts cancer cell expansion in the leptomeninges. Dendritic cell-generated cytokines drive proliferation of leptomeningeal NK cells The transcriptomic profiles of leptomeningeal NK cells, cytotoxic effectors capable of tumor cell killing were investigated next. Mouse leptomeninges contained naïve, activated, and proliferating NK cells. In the presence of cancer, a minor population of senescent NK cells was also apparent (Fig.5A and 5B, and Fig.23A to 23C). Human CSF demonstrated analogous populations of naïve-like and activated-like NK cells (Fig.23D to 23G). Independent of cancer, leptomeningeal Ifng overexpression induced increased NK cell proliferation; this effect was retained in NK cells isolated from Ifng overexpressing cancer-bearing animals (Fig.5C). Communication between leptomeningeal CCR7+ DCs and NK cells was examined next. As determined by CITE-seq, mouse leptomeningeal CCR7+ DCs specifically produced IL12 and IL15, two cytokines that promote survival and proliferation of NK cells; leptomeningeal NK cells expressed their cognate receptors (Fig.5D). To examine this putative cell-cell communication, mouse splenic NK cells in human CSF isolated from patients without LM was cultured. CSF represents a notoriously nutrient-sparse environment with minimal growth factors. Within CSF, naïve splenic NK cell survival was impaired; this effect was rescued by the addition of recombinant mouse IL12 and IL15 (Fig. 5E). Mirroring findings in mouse models, increased levels of NK cell-supporting cytokines was detected in the CSF from patients harboring LM (Fig.5F), as well as transcripts of their receptors in human leptomeningeal NK cells (Fig.5G). To demonstrate the role of NK cells in IFN-γ-dependent cancer control, NK cells in mice overexpressing Ifng were depleted in the AAV5 system described herein (Fig.14A and 14B). As expected, control of tumor growth and extended survival in mice treated with control antibody in the presence of leptomeningeal IFN-γ was observed (Fig.5H, and Fig.24). This phenotype was abolished in mice with antibody-depleted NK cells, supporting a model whereby NK cells serve as the leptomeningeal effector cells in the context of IFN-γ. NK cells in Ifngr1^-/- host mice were depleted next. In this epistasis experiment, NK cell depletion in mice with non-functional IFN-γ signaling did not further accelerate leptomeningeal cancer cell growth, confirming that IFN-γ signaling precedes NK cell-dependent cancer elimination (Fig.5I). Evidence of NK cell activation in human LM in the form of elevated levels of granzyme A, perforin, granulysin, and sFas as well as enrichment of activated NK cells in the CSF of LM patients was detected (Fig.5J and Fig.23D and 23F). Taken together, the data are consistent with a model whereby NK cell- and T cell-derived leptomeningeal IFN-γ acts on cDCs, supporting their maturation into CCR7+ DCs. These cells then produce a spectrum of lymphocyte- supporting cytokines, promoting NK cell proliferation and anti-leptomeningeal tumor action (Fig.6). Discussion The molecular interactions between metastatic cancer and immune cells within the leptomeninges is defined herein. To capture this complex oncologic ecosystem, a single cell transcriptional and proteomic profiling of clinical samples was employed. In doing so, IFN- γ was identified as a key mediator of anti-cancer response within the leptomeninges. To mechanistically dissect the growth suppressive action of leptomeningeal IFN-γ, several new immunocompetent animal models of LM were generated. Although leptomeningeal IFN-γ attracts myeloid cells into the leptomeningeal space, it does not promote anti-tumor activity in the macrophage population. Rather, leptomeningeal IFN-γ targets dendritic cells, promoting cDC2 maturation. Surprisingly, these dendritic cells orchestrate anti-cancer activity in an antigen-independent manner, generating cytokine signals to support the cytotoxic action of natural killer cells. LM represents a fundamentally inflammatory pathology. Indeed, LM was originally described as a “carcinomatous meningitis”, reflecting the characteristic abundant immune infiltrate and the purulent exudate found at autopsy. However, inflammatory signaling in the leptomeninges does not universally support LM. Herein, it is uncovered leptomeningeal inflammatory signaling that can interrupt cancer cell growth: IFN-γ. Elevation of leptomeningeal IFN-γ is identified as a hallmark of LM-induced pleocytosis across multiple tumor types. Moreover, higher CSF IFN-γ at diagnosis portends a more favorable prognosis for these patients. IFN-γ is a classical tumor-suppressive cytokine derived predominantly by Th1 CD4+ T cells, as well as CD8+ T cells, NK cells, NKT cells, and minor population of other immune cell types. Investigation of IFN-γ within the leptomeningeal space revealed anatomically distinct features: the proportion of immune cells expressing this protein, or its transcript, appeared to be insufficiently low even at in the absence of malignancy, suggesting that the leptomeninges actively maintain low production of this pleiotropic cytokine, possibly to impede neurotoxicity. IFN-γ stimulates the recruitment of a wide variety of immune cell types into the tumor microenvironment, particularly through the upregulation of CXC chemokines CXCL9, -10, and -11. The impressive pleocytosis in LM patients and experimental animal models can be, to some extent, explained by accumulation of these IFN-γ-regulated chemokines. However, both CC and CXC chemokines are dramatically elevated in the leptomeninges of patients harboring systemic inflammation or prolonged COVID-19, yet their accumulation does not necessarily result in clinically relevant CSF pleocytosis, suggesting additional level of immune cell entry control into the CSF. Unlike other anatomic compartments, the tumor-suppressive role of IFN-γ within the leptomeninges was unexpectedly independent of both the adaptive immune system and monocyte-macrophages. Instead, leptomeningeal DCs represent the essential IFN-γ target. The systems-level approach shown herein suggests that metastasis renders the leptomeningeal space an unusually dendritic cell-rich environment, when compared to extracranial sites with relatively sparse proportion of infiltrating dendritic cells. Indeed, cytometric analysis of STAT1 phosphorylation in the presence of LM was most apparent in DCs. Moreover, single-cell proteogenomic analysis of leptomeningeal DCs further suggested a previously underappreciated role of IFN-γ: cDC maturation into CCR7+, migratory dendritic cells. Trajectory analysis of mouse cDCs support the assertion that these CCR7+ DCs are predominantly a product of cDC2 maturation. In other, extracranial tumors, both cDC1 and cDC2 equally contribute to the migratory DC pool. In antigen- independent settings, these migratory DCs produce an array of immune cell pro-survival and proliferation factors. In the harsh leptomeningeal environment, DC-generated signals are necessary to sustain effector cell viability and activation. Herein, it is shown that NK cells proliferate more in the setting of Ifng overexpression, and that this is supported by the presence of migratory DC-derived signals including IL12 and IL15. Improved understanding of LM specific cancer cell-immune cell interactions suggests novel approaches to immune-oncology within the CNS and prompts a more nuanced view of the immune system in the leptomeningeal space. These findings demonstrate that leptomeningeal metastatic cancer cell growth is largely controlled by the innate immune system. Example 2: Methods Human CSF Cancer patients undergoing routine clinical procedures including spinal tap, Ommaya reservoir tap, or a ventricular shunt provided informed consent. CSF collected in excess of that needed for clinical care was reserved for this use under MSKCC Institutional Review Board-approved protocols 20-117, 18-505, 13-039, 12-245, and 06-107. Human CSF was processed, de-identified, and aliquoted. Cell-free CSF and CSF cell pellets were biobanked and stored at -80ºC until further analysis. Patient medical records and MRI scans were reviewed to confirm the LM status by neurooncologists (U.S., J.A.W., and A.B.), and clinical data necessary for this study was abstracted and de-identified. Giemsa-stained cytospins were part of routine diagnostic assessment and were retrieved and reviewed by neuropathologist (T.B.). Human single-cell transcriptomics Sample processing Freshly collected CSF obtained by lumbar puncture was placed on ice and processed within two hours, as described previously ¹, PBS-washed cells were encapsulated with Chromium Single Cell 3’ Library and Gel Bead Kit V2 (10x Genomics) and sequenced on an NovaSeq 6000 system (Illumina). Raw and pre-processed data were deposited to NCBI GEO under accession number GSE221522. Data preprocessing, initial processing, and batch correction Raw FASTQC files were pre-processed with SEQC with human reference genome hg38, and dense SEQC matrices were imported into Python. Each sample was plotted as a histogram of total counts per cell barcode on the log scale, resulting in a distribution with multiple modes and the threshold to remove the smallest mode, containing empty droplets and low-quality cells, was defined manually. Any genes that had counts equal to 0 after filtering were removed. To remove doublets, DoubletDetection method (parameters n_iter = 50, p_thres = 1e-7, voter_thres = 0.8) were run. Outer joined the individual samples to keep all detected genes, filtered cells to a minimum count of UMI = 100 and minimum total expressed genes of 100. Initially 22,051 cells and genes were detected and 20,676 high- quality cells and 18,322 genes were retained after filtering. ~1,497±898 genes per cell were detected, ~6,268±6,553 gene counts per cells, out of which 3.25±2.99% were mitochondrial genes (values represent mean ± one standard deviation). The library size was normalized, keeping raw count matrix for downstream analyses and removed any genes expressed in fewer than 5 cells. For downstream analysis, mitochondrial genes (prefix MT-), ribosomal genes (prefix RPS- or RPL-), and hemoglobin genes (prefix HB-) were further removed. Scanorama (default settings; kNN = 20) on the resulting AnnData object to batch correct across patients was analyzed. Batch correction was validated as follows: (i) cancer cells have higher inter-patient heterogeneity, suggesting absence of overcorrection, and (ii) only few quasi-cancer cells were identified from LM- patients after computational mixing (their presence was ruled out by pathologist during diagnostic cytology reading). This corrected matrix was employed for visualization, but not for individual gene comparisons. PCA (sc.pp.pca, n_components = 100) was then run. A k-nearest neighbor graph (kNN) was constructed based on 30 nearest neighbors and 100 principal components, using the scanorama 100-dimensional matrix (instead of PCA matrix). The cells were clusted with Leiden (resolution 2.0) and these Leiden clusters were merged according to major cell types, which were assigned based on marker gene expression. UMAP was computed with sc.tl.umap, using default parameters. The inter-patient heterogeneity was measured with Shannon entropy, Hj (Fig.7):

For each cell, the Shannon entropy measures the sample diversity of its nearest neighbors in the kNN graph. Each sample was subsampled to contain 500 cells. If samples are well- mixed, entropy of each cell will be high, while if samples are not well mixed entropies will tend to be low (this is true for cancer cells in general, which show extreme heterogeneity across patients). Human LM+ single-cell transcriptomic data was retrieved from NCBI GEO GSE150660. Raw and pre-processed data are available through NCBI GEO under accession number GSE221522. All ten human samples were collected between December 2017 and May 2018 and processed with the same pipeline. Subsetting of cells for downstream analyses and visualization Subsetting was performed by selecting cell clusters from major Leiden populations, shown in Fig.1B. For analysis of dendritic cells (DC), ‘cDC’ and ‘pDC’ clusters were subsetted and reclustered with sc.tl.umap and Leiden (resolution = 0.5). Cell type annotation was performed as follows: cDC1 cells are CLEC9A⁺XCR1⁺, cDC2 cells are CLEC10A⁺CD1C⁺, pDC cells are IRF7⁺TCF4⁺. Human LAMP3+ migratory dendritic cells are LAMP3⁺CCR7⁺ (orthologous to mouse CCR7+ DC). Two clusters bearing cDC2 signature were merged for further analyses. For analysis of natural killers (NK), ‘NK’ cluster was subsetted and reclustered with Leiden (resolution = 0.8), yielding in populations of cells with high SELL (CD62L) expression, further denoted as naïve-like, and populations with low SELL expression, denoted as activated-like and characterized by the expression of CXCR6. For analysis of both cell types, a Palantir was run with default settings (n_components = 5, knn = 30) that allowed us to access MAGIC-imputed (Markov affinity- based graph imputation of cells) cell counts, and these imputed cell counts were used only for visualization with 2D plots. UMAP, tSNE and heatmap plotting was performed using Scanpy and scVelo toolkits. Embedding density was computed with sc.tl.embedding_density (Fig.1C). For NK cell gene expression heatmap, counts were first zero-centered with sc.pp.scale (Fig.23). Code for pre-processing and downstream analysis is available from corresponding author and will be deposited to GitHub after peer review. Human CSF targeted proteomics Samples were processed and analysed. Biobanked CSF collected between 2015- 2020 was aliquoted and stored at -80°C at MSK Brain Tumor Center CSF Bank. Samples were slowly thawed on ice and 45 μL of CSF was mixed with 5 μL of 10% Triton X-100 (Sigma, T8787) in saline and incubated at room temperature for two hours (final concentration of Triton X-100 was 1%). Samples were then dispensed in a randomized fashion into 96-well PCR plates and stored at -80°C until further analysis. Relative levels of proteins in two targeted panels were detected using proximity extension assay (Olink Target 96 Inflammation and Olink Target 96 Neuro Exploratory, Olink). Protein abundance values are shown in NPX units (log2 scale). The analytical range for each analyte is available online (www.olink.com). Mouse strains and housing. All animal studies were approved by the MSKCC Institutional Animal Care and Use Committee under the protocol 18-01-002. Wild-type C57Bl/6 (JAX#000664) were purchased from Jackson Laboratory or bred in-house. C57Bl/6-Tyr^c-2 (JAX#000058, albino C57Bl/6) and BALB/c (JAX#000651) animals were purchased from the Jackson Laboratory. NSG animals were obtained from MSKCC RARC Colony Management Group. Purchased mice were allowed to habituate for at least one week before manipulation and experimentation. Transgenic lines on C57Bl/6 background were purchased from the Jackson Laboratory and bred in-house: Ifng knock-out line (B6.129S7-Ifng^tm1Ts/J, JAX#002287), Ifngr1 knock-out line (B6.129S7-Ifngr1^tm1Agt/J, JAX#003288), Rag1 knock- out line (B6.129S7-Rag1^tm1Mom/J, JAX#002216), double-reported knock-in/knock-out Cx3cr1^GFP/GFPCcr2^RFP/RFP (B6.129(Cg)-Cx3cr1^tm1Litt Ccr2^tm2.1Ifc/JernJ, JAX#032127). For homozygous breeding, breeding pairs and randomly selected progenies used in the experiments were genotyped as recommended. For experiments that involved bioluminescent imaging where wild-type animals were not compared to transgenic lines, albino C57Bl/6-Tyr^c-2J animals were used. Mice in all experimental groups were age- (± 4 days), sex-, and fur color-matched. Mice used in this study were housed in a specific pathogen-free conditions, in an environment with controlled temperature and humidity, on 12-hour light/dark cycles (lights on/off at 6:00 am/pm), and with access to regular chow and sterilized tap water ad libitum. Cell culture Mouse lung cancer LLC sublines were described previously. Mouse breast cancer E0771 cells were kind gift from Dr. Ekrem Emrah Er. B16-F10 (CRL-6475), Yumm5.2 (CRL-3367), EMT6 (CRL-2755), and 4T1 cells (CRL-2539) were obtained from ATCC. LentiX 293T cells (#632180) were obtained from Takara. PlasmoTest HEK Blue-2 cells (rep-pt1) were obtained from Invivogen. LLC, E0771, and B16 sublines and LentiX 293T and HEK Blue-2 cells were maintained in high-glucose DME (MSKCC Media Core), supplemented with 10% fetal bovine serum (FBS; Omega Scientific #FB-01) and 1% penicillin-streptomycin (P/S; Gibco #15140163) or 1x Primocin (Invivogen #ant-pm-2). Yumm5.2 sublines were maintained in high-glucose DME:F12 (MSKCC Media Core), supplemented with 10% FBS, 1% non-essential amino acids (Gibco #11140050) and 1% P/S or 1x Primocin.4T1 sublines were maintained in RPMI (MSKCC Media Core), supplemented with 10% FBS and 1% P/S or 1x Primocin. EMT6 sublines maintained in Waymouth’s (MSKCC Media Core), supplemented with 10% FBS and 1% P/S or 1x Primocin. Cell lines were subcultured at least twice a week, replaced approximately after six weeks in culture with new stocks, stored in liquid nitrogen, and routinely tested negative for mycoplasma contamination. Proliferation of vehicle- or recombinant mouse IFN-γ- exposed (Biolegend #714006) cancer cells in vitro was measured with CellTiter-Glo luminescent cell viability assay (Promega G7572) 72 hours after seeding 500 cells per well into 96-well, white-walled plate (Corning). Genetic engineering of mouse cancer cell lines Plasmid DNA was amplified in NEB Stable Competent E. coli (New England Biolabs #c3040i) or other E. coli strains provided by vendors, grown in LB broth (MSKCC Media Core) overnight and isolated with ZymoPURE II kit (Zymo Research #D4203). Mouse cancer cell lines generated in this study were engineered to constitutively express V5-tagged Firefly luciferase (pLenti-PGK-V5-Luc-Puro^w543-1, Addgene #19360), kind gift from Dr. Eric Campeau and Dr. Paul Kaufman. Some LeptoM derivatives (LLC LeptoM, E0771 LeptoM, B16 LeptoM) used in the flow cytometry experiments were additionally engineered to constitutively express AmCyan fluorescent protein (pLV-EF1a-AmCyan1- IRES-Puro, Takara #0039VCT). Lentiviral constructs for CRISPR-Cas9 editing in the pLV- hCas9:T2A:Bsd backbone were synthetized by VectorBuilder. sgRNA sequences expressed under the control of U6 promoter were as follows: sgLacZ - ‘TGCGAATACGCCCACGCGAT’, sg Ifngr2#1 ‘TGGACCTCCGAAAAACATCT’, sgIfngr2#2 ‘AGGGAACCTCACTTCCAAGT’, sg Ifngr2#3 ‘TCTGTGATGTCCGTACAGTT’. Lentiviral particles were prepared with LentiX 293T cell line using ecotropic, VSV-G pseudotyped lentiviral system and concentrator (Takara #631276 and #631232), as recommended. Mouse cancer cell lines were spin-transduced (1000 g, 32ºC, 1 hour) with concentrated lentiviral particles in complete culture medium containing 5 μg/mL hexadimethrine bromide (Santa Cruz, #sc-134220) and selected for 5-7 days in complete medium containing 2-5 μg/mL puromycin (Gibco, #A1113802) or 5-10 μg/mL blasticidin (Invivogen, ant-bl-1). CRISPR-Cas9 edited lines and control clones were single-cell sorted into 96-well plate. Gene function was assessed functionally (LLC, E0771, and B16 LeptoM), and DNA editing was confirmed with Sanger sequencing (LLC and E0771 LeptoM; not shown) after expansion. Cancer cell injections Cancer cells were injected into mice between 6 and 16 weeks of age. Mice were deeply anesthetized in an insulated chamber perfused with 2-3% isoflurane (Covetrus; #11695067772) in medical air or with intraperitoneally delivered mixture of ketamine (100 mg/kg) and xylazine (10 mg/kg) in ultra-pure, sterile, and pyrogen-free water for injection. Female mice were used for breast cancer models and both males and females in approximately 1:1 ratio for melanoma and lung cancer models, if not stated otherwise. Mice deceased within 72 hours of injection were excluded from further analysis. Mouse hair was removed from the injection site, and the area was sterilized three times with ethanol. For intracisternal injection, 10 μL of cancer cell suspension in PBS was introduced into the cisterna magna using Hamilton syringe (Hamilton #HT80501) fitted with a 30G needle, as described previously with minor modifications. Briefly, mouse was positioned prone over a 15 mL conical tube to place cervical spine in flexion. The occiput was palpated, the needle was advanced 4 mm deep, and the syringe content was slowly released into the cisterna magna. The syringe was then held in this position for another ten seconds and then carefully ejected to prevent the reflux of injected liquid. This procedure was tolerated well by the animals (success and survival rate > 95%). Mice displaying neurologic symptoms upon awakening were immediately euthanized. The number of cancer cells introduced intracisternally was: 2,000 cells for LLC LeptoM, 4,000 cells for E0771 LeptoM, and 500 cells for B16 LeptoM, Yumm5.2 LeptoM, EMT6 LeptoM, and 4T1 LeptoM cells. For intracardiac injections, 10,000 cells (for 4T1 or EMT6 sublines) or 50,000 cells (all other sublines) was injected in 50 μL saline using 28G insulin syringe into the left cardiac ventricle. For extracranial injections, cells were injected in 50 μL percutaneously into the fourth mammary fat pad (E0771 LeptoM; 500,000 cells), subcutaneously (LLC LeptoM; 200,000 cells), or intradermally (B16 LeptoM; 100,000 cells) using 28G insulin syringe. Quantification of tumor burden. The spread and growth of cancer cell lines engineered to express V5-tagged Firefly luciferase (lucV5) was monitored using non-invasive bioluminescent imaging (BLI). Mice were anesthetized in an insulated chamber perfused with 2-3% isoflurane in medical air and injected retro-orbitally with 50 μL of sterile D-luciferin (15 mg/mL, Goldbio #LUCK-5G) solution in PBS. BLI was captured using IVIS Spectrum-CT (Perkin Elmer). Data were recorded and processed with Living Image (v4.7.2) software. Recorded images were quantified as cranial radiance. For the rare occasion when mice on C57Bl/6 background (without tyrosinase mutation) developed melanin spots preventing luciferase imaging, these animals were not included in the imaging analysis. Tumors in the mammary fat pad, intradermal and subcutaneous tumors were measured with calibrated digital calipers (VWR #62379-531). Tumor volumes are expressed as the product of the two largest diameters. Quantification of leptomeningeal tumor burden with image analysis B16 melanoma sublines growing in 3D structures produce high amounts melanin that quenches light in a wide spectrum of wavelengths, interfering with accurate bioluminescent and fluorescent imaging. For these tumors, bioluminescence was therefore used solely to confirm the presence or identify the anatomic location of cancer. To overcome this limitation and to accurately quantify the tumor burden in B16 LeptoM model, brains from intracisternally injected mice were dissected, preserving the plaques of cancer, and fixed in formalin overnight. Brains were then carefully washed with tap water and placed into 6-well dishes in 70% ethanol. Brightfield images of fixed brains (basilar plane) were taken using Lumar Stereoscope (Zeiss) against dark background. Data were processed with Fiji/ImageJ (v2.0.0, NIH) as follows: images were converted to 8-bit, each brain was manually encircled, and its area was recorded. The threshold for plaque measurement was first estimated in a small cohort to capture only the plaque areas, and then applied to all subsequent measurements. Percentage of the area of cancer plaques covering the basilar surface of the brain was calculated as the area of plaques divided by the area of brain and multiplied by 100. Since the 8-bit images were monochromatic, this method showed to be robust and reproducible throughout different measurements. Five control brains from mice without cancer, collected for different purposes, were measured and the area of darker structures above the pre-set threshold was less than 1% using this method. Derivation of leptomeningeal and parenchymal metastatic cell lines BrM cell lines (brain parenchyma-tropic) 50,000 parental cells were injected intracardially. Hematogenous dissemination was confirmed with BLI approximately 1 hour after injection. Upon confirmation of brain colonization with BLI and development of late-stage cancer symptoms, mice were re- injected with luciferin and euthanized. Brains were dissected and imaged ex vivo to confirm colonization of parenchyma. Brains with overt lesions were minced, mechanically dissociated using GentleMACS (Miltenyi Biotec) and digested in a mixture of collagenase (100 U/mL, Worthington #LS005273) and DNAse I (10 U/mL, Worthington #LS006333) in HG DME for 1 hour at 37ºC, mechanically dissociated every 20 minutes. Suspension was then washed, filtered through a 70-micron mesh, and seeded into corresponding complete culture media, in which P/S was replaced with Primocin. The medium was changed every day for three days, then every other day. Growing cancer cell colonies were expanded for three passages and named BrM1. These cells were then again injected intracardially and the whole procedure was repeated, leading to the establishment of BrM2 cell lines, competent to colonize brain parenchyma after hematogenous dissemination. LeptoM cell lines (leptomeninges-tropic) 2,000 lucV5-expressing parental cancer cells in 10 μL saline were injected intracisternally. Presence in the CSF was confirmed with BLI approximately one hour after injection. Mice were monitored weekly using BLI and daily checked for the presence of pathophysiological symptoms. When these mice developed neurologic symptoms (moribund behavior, head tilt, seizures, overall weakness) and cancer presence in the CSF was indicated by BLI, luciferin was injected retro-orbitally, and mice were euthanized. Brain was dissected as described in and basilar side of brains as well as basilar meninges of mouse were assessed with BLI post mortem. The cranial cavity and brain surface were then washed with approximately 3 mL of saline. This volume was collected, pelleted, resuspended in complete media containing Primocin and maintained as described above for BrM cells. This procedure was repeated once for melanomas or three times for epithelial cancers, leading to the establishment of Inter cell lines. These Inter cells were then injected intracardially and mice were monitored with BLI and treated as described above. Successfully expanded cancer cells that were isolated from these intracardially injected mice were capable to grow colonize leptomeninges and growth in the CSF, hence named LeptoM cells. Three to five biological independent sublines were successfully established per cell lines. For transcriptomic analyses, these replicates were processed separately retaining the ID of founder mice. For further in vitro and in vivo manipulations, these replicates were pooled (in one-to-one etc. ratios) and maintained under sub-confluent conditions in vitro for limited number of passages (less than 12). RNA collection and extraction, and transcriptomic analysis Cancer cell lines were collected 24 hours after initial seeding of approximately 1x10⁶ cells per 100 mm plate by direct lysis with RLT buffer (Qiagen, component of RNeasy kits). RNA from cell lines was isolated with RNeasy Plus Mini Kit (Qiagen #74136), and sequenced and analyzed. Resulting HTSeq matrices from bulk transcriptome were processed in R Studio with DESeq2. Data from LLC cell lines was retrieved from NCBI GEO GSE83132. Newly generated raw and pre-processed data are available through NCBI GEO under accession number GSE221358. Collection of mouse CSF and leptomeningeal immune cells Mice were deeply anesthetized using ketamine/xylazine and transcardially perfused with sterile, ice-cold PBS. Mice were positioned as described in ‘Cancer cell injections’ section, and CSF was collected through the cisternal puncture into the PBS-flushed syringe fitted with a 30G needle. Approximately 15 μL of CSF was collected from each single mouse using this procedure. Blood-contaminated samples were discarded. CSF was flash- frozen on dry ice and stored at -80ºC until analysis; or diluted in 200 μL of 4% methanol- free paraformaldehyde (Electron Microscopy Sciences #15714-S) and spun onto microscopic slides to produce cytospins. These were then left to air-dry and stained with hematoxylin QS (Vector Biolabs #H-3404-100). Leptomeningeal immune cells were collected and processed further for downstream applications, as described in corresponding sections. Intracisternal delivery of AAV particles Mouse Ifng [NM_008337.4] or Egfp sequences were inserted into AAV expression vector (pscAAV backbone under the control of CMV promoter) and used for packaging into AAV5 particles that were ultra-purified for in vivo applications (VectorBuilder). Genomic content (GC) was estimated with PCR.5 μL of vehicle-diluted AAV5 suspension (1x10¹³ GC/mL) was slowly infused into mouse leptomeninges intracisternally and mice were allowed to rest for at least 2 weeks before further manipulation. Intracisternal delivery of recombinant proteins Vehicle (PBS), or a 10 ng or 25 ng dose of recombinant mouse IFN-γ (Biolegend #714006) in total volume of 10 μL was initially delivered with cancer cell injection, followed by weekly administration, as described above. Heat inactivated IFN-γ was prepared by incubating vehicle or vehicle-diluted IFN-γ at 95ºC for 15 min and allowed to cool on ice before administration. Mouse single-cell proteogenomics Sample processing. Cx3cr1^GFP/GFPCcr2^RFP/RFP mice were crossed with wild-type C56Bl/6 mice and the resulting female and male Cx3cr1^+/GFPCcr2^+/RFP progeny was intracisternally infused with AAV and LLC LeptoM cancer cells, as described above and in Fig.19. Leptomeningeal cells from six animals per group were isolated and resuspended in Cell Staining Buffer (Biolegend #420201). In total, leptomeningeal immune cells are profiled from 24 mice and 4 different conditions. To limit the non-specific antibody binding, cells from each mouse were incubated with TruStain FcX (Biolegend #101320), subsequently barcoded with TotalSeq-A anti-mouse hashtags 1 to 6 (Biolegend), listed in table S4, and washed. Cells from these six mice were then pooled, resulting in four independent samples, and stained with a custom TotalSeq-A panel (Biolegend) consisting of 198 antibodies targeting cell surface epitopes and non-targeting isotype controls, listed in table S5, to facilitate identification and origin of selected immune cell types (such as in fig.21H and 21I). Dead cells and debris were removed with LeviCell (LevitasBio), washed cells were counted, encapsulated with Chromium Single Cell 3’ GEM Library and Gel Bead Kit V3.1 (10x Genomics), and sequenced on NovaSeq 6000. Quality control plots are shown in fig.19. Raw and pre-processed data are available through NCBI GEO under accession number GSE221593. Code for pre-processing and downstream analysis is available from corresponding author and will be deposited to GitHub after peer review. Data preprocessing and initial processing Raw FASTQC files were pre-processed with SEQC with modified mouse reference genome mm10 that included GFP, RFP and AmCyan sequences, and pre-processed as human samples, with the exception that no batch correction was applied. Each sample was processed separately. Cell filtering and doublet removal with DoubletDetection (p_thresh=1e-16, voter_thresh=0.5, n_iters=25, use_phenograph=False, standard_scaling=True) was performed as described above for human samples, 54,781 cells and 20,804 genes were detected and 46,852 high-quality cells and 18,277 genes after filtering out low quality cells and non-immune cell populations was retained. ~1,387±866 genes per cell was detected, ~4,374±5,483 gene counts per cells, out of which 3.15±2.62% were mitochondrial genes (values represent mean ± one standard deviation). Shannon entropy for this uncorrected mouse dataset was computed as described above for human data. AnnData files for each sample were then merged after filtering and doublet removal by an outer join. Erythrocyte genes (HBA-A1, HBB-BT, HBA-A2, HBB-BS, ALAS2, HBB-BT, HP, and BPGM) and CD41 protein signal (platelet marker) were filtered out, in an addition to mitochondrial (prefix MT-) and ribosomal genes (prefix RPS- or RPL-). HTO and CITE-seq data were demultiplexed with cite-seq-count, using default parameters applied on the whitelist of cells that passed the filtering step based on RNA quality, as described above. RNA and protein data (HTO and CITE) were integrated with totalVI, facilitating identification of immune cell subtypes using both gene and surface protein expression (default settings with top 4,000 HVG). HTOs were assigned based on maximum number of observed counts (as shown in Fig.19E). UMAP kNN graph and Leiden clustering in this dataset was computed using sc.pp.neighbors and totalVI processed latent variables. Leiden clusters were merged according to major cell types, which were assigned based on marker gene and surface protein expression, as showed in Fig.9. (HVG - highly variable genes). Subsetting of cells for downstream analyses, plotting and visualization Plotting was performed using Scanpy (UMAP, tSNE, heatmaps) and scVelo (UMAP, tSNE; this package was not used to infer RNA velocity). Embedding density was computed with sc.tl.embedding_density (Fig.2C). Cell cycle prediction was adapted from tl.score_genes_cell_cycle (Fig.4F and 5C). Subsetting was performed by selecting cell clusters from major populations, shown in Fig.2B. Cells from all four conditions were included, shown in Fig.19: cells isolated from naïve, vehicle-injected or LLC LeptoM- injected animals that were overexpressing Egfp (control gene) or Ifng specifically in the leptomeninges. For analysis of dendritic cells (DC), ‘cDC’ and ‘pDC’ clusters were subsetted, these cells were expressing CD11c (pan-DC marker) on cell surface. For analysis of natural killer cells (NK), ‘NK’ and ‘Proliferative T/NK’ clusters were subsetted to ensure proper representation of all NK cells. These cells were reclustered with Leiden (resolution = 0.7), and clusters expressing CD3 and TCRβ cell surface markers were excluded, retaining only bona fide NK cells, characterized as Nk1.1⁺ CD3- TCRβ-. For analysis of both cell types, Palantir was run (default settings - n_components = 5, knn = 30) that allowed us to (i) compute diffusion components, used for tSNE re-embeddings and (ii) access MAGIC- imputed (Markov affinity-based graph imputation of cells) cell counts (Fig.4C, 5A, and 5D). These imputed cell counts were used only for visualization with 2D plots. tSNE plots were re-fitted using multiscale coordinates that are based on diffusion components obtained with Palantir (n_components=5, knn=30). Subsetted DCs were refitted onto tSNE using Palantir multiscale coordinates and annotated with initial Leiden loadings to identify four typical dendritic cell populations. Both gene expression data (shown as a heatmap in Fig. 20A) and cell surface signals: cDC1 cells are Xcr1⁺, cDC2 cells are CD11b⁺, pDC cells are B220⁺, while CCR7+ cells express CCR7 gene (Fig.4B and 21D). Subsetted NK cells were refitted onto tSNE using Palantir multiscale coordinates and re-clustered with Leiden (resolution = 0.3), that resulted in identification of four putative cell states. Naïve NK cells expressed high cell surface levels of CD62L (encoded by SELL gene), while activated and proliferative cells had low CD62L levels. Proliferative cells also expressed genes associated with cell cycling, such as MKI67, TOP2A, and HMGB2. Senescent cells expressed CD55 and KLGR1 on their cell surface (Fig.5B). Cancer cells, characterized by the expression of keratin genes and CD63, were subsetted as ‘cancer’ cluster and visualized with UMAP without re-embedding. Cancer cell gene signatures were computed with GSEApy (Fig.21, B and C; cut-offs are provided in corresponding figure legends). Trajectory analysis To predict the maturation trajectories of conventional dendritic cells in normal, non- perturbed steady-state mouse leptomeninges and leptomeninges with metastasis, CD11c- positive cDC cells were subsetted from naïve and cancer-bearing mice overexpressing Egfp only (‘cDC’ cluster and ‘egfp’ condition). CellRank was first used to identify putative trajectories without the need for initial or terminal state selection. Genes present in less than 10 cells were normalized counts per cell and with log(X+1) and extracted HVGs with Scanpy’s functions sc.pp.filter_genes, sc.pp.normalize_total, sc.pp.log1p, and sc.pp.highly_variable_genes.2,635 cells and 2,090 cDC-expressed HVG were retained. PCA was recomputed with sc.pp.pca (n_comps = 50, zero_centered = True) and refitted the tSNE plot with top 9 diffusion components in multiscale space (n_components=9, knn=15), this tSNE map was used for further visualization. cytoTRACE kernel was used that allowed us to assess plausible and biologically traceable cell transitions, following their trajectory from more primitive to mature cells. Gene counts were then imputed from normalized and filtered count matrix with scv.pp.moments with default parameters (n_pcs = 30 , n_neighbors = 30) and initialized CellRank’s cytoTRACEkernel with default parameters. Transition matrix was computed (threshold_scheme = hard). Given that this approach provides qualitative insights into the transition matrix by iteratively choosing the next cell based on the current cell’s transition probabilities, two additional settings were compared: (i) it was not specified from which cells or condition to select starting point (start_ixs = None), or (ii) all cells were selected from naïve Egfp-overexpressing mouse as the starting points. Both approaches identified CCR7+ DCs as mature endpoints, and to remain agnostic to the initiation, the analysis was continued without initial cells or states being defined (n_sim = 100). GPCCA estimator (Generalized Perron Cluster Cluster Analysis) was used to coarse-grain a discrete Markov chain into a set of macrostates, and compute coarse- grained transition probabilities among the macrostates. Three macrostates were identified and assigned each cell their dominant microstate membership. These results suggested that the cDC2 population is prone to maturate towards CCR7+ DCs, with insignificant contribution of cDC1 population (Fig.21F to 21H). CellRank prediction was corroborated by analysis with Palantir (n_components = 9, knn = 15, num_waypoints = 500) that identified cDC2 population as the one with the highest entropy (maturation potential), and this observation was robust to change in the number of diffusion components, neighbors, or waypoints (Fig.21I and 21J). The cDC2-to-CCR7 DC transition axis was detected and plotted as smoothened gene trends along predicted Palantir pseudotime axis (Fig.4D). Bone marrow chimeras Male C57Bl6-Tyr^c-2 mice were initially anesthetized with 2-3% isoflurane in medical air and restrained in ventilated conical plastic tubes. Animals were placed in a prone position and irradiated using X-RAD320 irradiator (Precision; North Branford, CT, USA) with the following settings: 250kV; 12mA; using 0.25 mm copper filter; distance of radiation source to the animal body: 50 cm; irradiation field: 20 × 20 cm; dose rate: 117.5 cGy/min. Five animals were fitted into the radiation field and received and two cycles of 5.5 Gy total body radiation 6 hours apart. Immediately after completion of the irradiation procedure, animals were returned to their cages and fed with sulfatrim-enriched diet for the duration of this experiment. Within 24 hours, mice were retro-orbitally infused with approximately 1x10⁷ bone marrow cells from multiple pooled wild-type or Zbtb46-DTR^+/+ C57Bl/6 donors. Bone marrow cells were sterilely isolated from femur and tibia. Inner bone marrow was exposed and placed inside a 0.6 mL PCR tube with small hole punched in the bottom. The PCR tube was placed in 1.5 mL microcentrifuge tube and the samples were spun down to collect and pellet the bone marrow cells. Cells were counted and resuspended in sterile PBS. Immune cell depletions Monocyte-macrophages were depleted with rat anti-mouse CSF1R antibody (Bio X Cell #BE0213), rat IgG2a isotype was used as control (Bio X Cell #BE0089). Antibodies were diluted in in sterile pH 7.0 (BioXCell #IP0070) and delivered intraperitoneally. An initial dose of 400 μg was injected one day before cancer cell implantation, followed by tri- weekly injection of 200 μg. Monocyte-macrophages were also independently depleted with anionic clodronate liposomes, vehicle-containing liposomes were used as control (Clophosome®-A and Control Liposomes, FormuMax Scientific #F70101C-AC-10). Liposomes were delivered retro-orbitally. Initial dose of 200 μL was injected one day before cancer cell implantation, followed by bi-weekly injection of 100 μL. cDC progenitors were depleted in bone marrow chimers that received wild-type or Zbtb46- DTR^+/+ donor cells with diphteria toxin (DTx; Sigma #D0564), diluted in PBS, and delivered intraperitoneally. Initial dose of 400 ng was injected one day before cancer cell implantation, followed by bi-weekly injection of 100 ng. Both wild-type and Zbtb46- DTR^+/+ cohorts were receiving DTx. NK cells were depleted with polyclonal rabbit anti- mouse asialo GM1 (Poly21460; Biolegend #146002), rabbit polyclonal IgG was used as control (Invitrogen #02-610-2). Both antibodies were reconstituted with PBS. Initial dose of 50 μg was instilled one day before cancer cell implantation, followed by bi-weekly injections of 50 μg. Flow cytometry Single-cell suspensions were prepared as described above. After filtering though 70- micron filter and washing with 2 mM EDTA and 1% BSA in PBS, nonspecific binding sites were blocked with TruStain FcX (Biolegend #101320) diluted in PBS, supplemented with 10% rat serum (Sigma #R9759) for 10 min on ice. Antibodies against surface antigens were diluted in reconstituted Brilliant Stain Buffer Plus (BD #566385), supplemented with 5% rat serum. Surface antigens were stained for 15 min on ice. LIVE/DEAD Green/Violet/FarRed Dead Cell Stain kits (Life Technologies #L34969, L34963, L34973, respectively), DAPI (Molecular Probes #D1306) or propidium iodide (Thermo Fisher #P3566) were used as viability stains. Buffer without BSA was used before LIVE/DEAD staining, which was performed for 15 min on ice. Red blood cells were lysed with 1X ACK buffer or 1x eBioscience RBC Lysis Buffer (Invitrogen #00-4300-54) for 5 min at ambient temperature. For cytokine production analysis, leptomeningeal isolates were resuspended in serum-free IMDM and incubated (MSKCC Media Core) with or without addition of brefeldin A (Biolegend # 420601), ionomycin (StemCell Technologies # 73722), and phorbol 12-myristate 13-acetate (PMA; Invivogen # tlrl-pma), for 2 hours at 37ºC. Where the intracellular staining was performed, cells were further fixed with IC Fixation Buffer for 20 min (Invitrogen, 00-8222-49) at room temperature, permeabilized and stained with antibodies against intracellular markers in 1x Permeabilization Buffer for 1 h (Invitrogen, 00-8333-56) and analysed. For pSTAT1 transcription factor staining, cells were processed using True-Nuclear Buffer Set (Biolegend #424401) or FOXP3 Fix/Perm Buffer Set (Biolegend #421403) and analysed. MHC class I levels of vehicle- or recombinant mouse IFN-γ-exposed (Biolegend #714006) cells in vitro was measured 24 hours after treatment. Data was recorded using LSR Fortessa (BD). Gating and analysis was performed essentially as described in ^1,23, using unstained samples, isotype-stained samples, and/or FMO controls. Soluble protein detection in plasma and CSF Solute analytes in the human and mouse CSF were analyzed using following multiplexed bead arrays, used as recommended by the manufacturer: LEGENDPlex mouse anti-virus response (Biolegend #740622), LEGENDPlex human CD8/NK panel (Biolegend #740267). NK cell in vitro survival assay NK cells were enriched from dissociated spleens of female and male C57Bl/6 mice with MojoSort mouse NK cell isolation kit (Biolegend #480049). Approximately 20,000 cells were seeded into 1:1 mixture of HG DME and human CSF from cancer patients without LM, containing 10 ng/mL recombinant human IL2 (Biolegend #589102), into 96- well plate. Cells were incubated for 24 h with or without the addition of 1 ng/mL or recombinant mouse IL12p70 (Biolegend #577002) and recombinant mouse IL15 (PeproTech #210-15-10ug). Viability and cell counts were assessed with cytometry. Histology Tissue from euthanized mice was fixed in 10% formalin overnight, thoroughly washed in tap water, sliced, and stored in 70% ethanol until embedded into paraffin. Paraffin-embedded blocks were then cut into 5 micron thick sections and placed onto microscopic slides. Hematoxylin & eosin (H&E) stains were performed by MSKCC Molecular Cytology Core. Myelin stain was performed with Luxol Fast Blue stain kit (Abcam #ab150675). Immunofluorescence was performed as described in ¹, using following primary antibodies: CD11c (hamster, 1:50, Novus #NBP1-06651 and #NB110- 97871, used in combination); Cleaved Caspase 3 (rabbit, 1:200, Cell Signaling Technology #9661S); CNPase (mouse, 1:1000, Abcam #ab6319); DCX (sheep, 1:200, R&D #AF10025); GFAP (goat, 1:500, Abcam #ab53554); Iba1 (rabbit, 1:500, Invitrogen #PA5- 27436; and goat, 1:500, Novus #NB100-1028), MBP (mouse, 1:100, R&D #MAB42282); NeuN (mouse, 1:100-1:500, Sigma #MAB377); Olig2 (goat, 1:200, R&D #AF2418). AF488-, Cy3-, and AF647-conjugated, anti-mouse, goat, rabbit, and sheep secondary antibodies were obtained from Jackson ImmunoResearch; AF647-conjugated anti-hamster secondary antibody was obtained from Abcam. For antibodies of murine origin applied on mouse tissue, the endogenous IgG was first blocked with reconstituted VisUBlock Mouse (R&D #VB001-01ML). DAPI (Molecular Probes #D1306) was used as nuclear counterstain. Autofluorescence was quenched with Vector TrueView (Vector Laboratories #sp-8400). Slides were scanned with Mirax slide scanner (Zeiss), and images for further analysis were exported with CaseViewer (3DHISTECH). Quantification of immunofluorescence imaging Quantification of Iba1+ myeloid cells in choroid plexus was performed. Cleaved Caspase 3-positive cells in cancer plaques and clusters in leptomeninges were counted manually in FOVs of approximately equal size. Cancer plaques in timepoint-matched AVV5-Ifng animals are rare; 2-3 FOVs per brain were extracted and the exact animal sample size and number of FOVs is stated in the corresponding images. Analysis of NeuN was done in the motor and somatosensory cortex in two regions. Region #1 covers layers 1- 4 and region #2 covers layer 5 and 6. One section per animal was analysed and the chosen sections were spanning levels -0.18 to -0.196 relative to bregma. Olig2 was quantified in the corpus callosum, spanning a lateral area from 0-1.7 mm relative to bregma; and together with CNPase in also in subcortical and cortical region above corpus callosum. All image analyses were performed in Fiji/ImageJ. Statistical analysis and reproducibility Plotting and statistical analysis was performed with Prism 8.1.0 (GraphPad Software), using Mann-Whitney U test, unless specified otherwise. In the box plots (box & whisker plots), box extends from 25^th to 75^th percentile and whiskers show minimum to maximum values. Results from single-cell analyses were plotted in Python. Bulk RNA-seq was processed in R Studio. Whenever possible, mice were randomly allocated into treatment groups. This was not possible in experiments with transgenic animals. Investigators were not blinded to genotype or treatment over the course of experiment. Sample size and exact P values are included in figures. Sample sizes were not pre- determined. Critical mouse experiments were reproduced by two independent investigators. Animal exclusion criteria for animal experiments (death within three days of injection or appearance of pigmented spots that interfered with BLI) are described above. No human samples were excluded from analyses. Incorporation by Reference All publications, patents, and patent applications mentioned herein are hereby incorporated by reference in their entirety as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control. Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Claims

What is claimed is: 1. A method of treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for at least one IL-12 peptide, at least one IL-15 peptide, and/or at least one interferon peptide.

2. A method of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for at least one IL-12 peptide, at least one IL-15 peptide, and/or at least one interferon peptide.

3. The method of claim 2, wherein the subject is afflicted with leptomeningeal metastasis.

4. The method of any one of claims 1 to 3, wherein the viral vector is an adeno associated viral vector.

5. The method of claim 4, wherein the adeno associated viral vector is an AAV5 vector.

6. The method of any one of claims 1 to 5, wherein the viral vector targets the meninges.

7. The method of any one of claims 1 to 5, wherein the viral vector targets the choroid plexus.

8. The method of any one of claims 1 to 7, wherein the at least one interferon peptide is a gamma interferon peptide.

9. The method of any one of claims 1 to 7, wherein the at least one interferon peptide is an alpha interferon peptide.

10. The method of any one of claims 1 to 9, wherein the peptide is a modified peptide.

11. The method of any one of claims 1 to 10, wherein the viral vector is administered intrathecally.

12. The method of any one of claims 1 to 11, wherein the method further comprises administering an immune checkpoint inhibitor to the subject.

13. The method of claim 12, wherein the immune checkpoint inhibitor is an inhibitor of an immune checkpoint protein selected from CTLA-4, PD-1, VISTA, B7-H2, B7-H3, PD- L1, B7-H4, B7-H6, ICOS, HVEM, PD-L2, CD160, gp49B, PIR-B, KIR family receptors, TIM-1, TIM-3, TIM-4, LAG-3, BTLA, SIRPalpha (CD47), CD48, 2B4 (CD244), B7.1, B7.2, ILT-2, ILT-4, TIGIT, HHLA2, butyrophilins, A2aR, and combinations thereof.

14. The method of claim 13, wherein the immune checkpoint inhibitor is an inhibitor of PD-1 or PD-L1.

15. The method of any one of claims 12 to 14, wherein the at least one peptide and the immune checkpoint inhibitor are administered conjointly.

16. The method of any one of claims 1 to 15, wherein the cancer is lung cancer, a breast cancer, a colon cancer, a cervical cancer, a pancreatic cancer, a renal cancer, a stomach cancer, a GI cancer, a liver cancer, a bone cancer, a hematological cancer, a neural tissue cancer, a melanoma, a thyroid cancer, a ovarian cancer, a testicular cancer, a prostate cancer, a cervical cancer, a vaginal cancer, or a bladder cancer.

17. The method of claim 16, wherein the cancer comprises a tumor.

18. The method of claim 17, wherein the tumor is an adenocarcinoma, an adrenal tumor, an anal tumor, a bile duct tumor, a bladder tumor, a bone tumor, a brain/CNS tumor, a breast tumor, a cervical tumor, a colorectal tumor, an endometrial tumor, an esophageal tumor, an Ewing tumor, an eye tumor, a gallbladder tumor, a gastrointestinal, a kidney tumor, a laryngeal or hypopharyngeal tumor, a liver tumor, a lung tumor, a mesothelioma tumor, a multiple myeloma tumor, a muscle tumor, a nasopharyngeal tumor, a neuroblastoma, an oral tumor, an osteosarcoma, an ovarian tumor, a pancreatic tumor, a penile tumor a pituitary tumor a primary tumor a prostate tumor a retinoblastoma a Rhabdomyosarcoma, a Salivary gland tumor, a soft tissue sarcoma, a melanoma, a metastatic tumor, a basal cell carcinoma, a Merkel cell tumor, a testicular tumor, a thymus tumor, a thyroid tumor, a uterine tumor, a vaginal tumor, a vulvar tumor, or a Wilms tumor.

19. A method of treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for IL-12 and/or IL-15.

20. A method of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer, the method comprising administering to the subject a viral vector that encodes for IL- 12 and/or IL-15.

21. A method of treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject at least one IL-12 peptide, at least one IL- 15 peptide, and/or at least one interferon peptide.

22. A method of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer, the method comprising administering to the subject at least one IL-12 peptide, at least one IL- 15 peptide, and/or at least one interferon peptide.

23. The method of claim 22, wherein the subject is afflicted with leptomeningeal metastasis.

24. The method of any one of claims 21 to 23, wherein the at least one IL-12 peptide is a modified IL- 12 peptide.

25. The method of any one of claims 21 to 23, wherein the at least one IL-15 peptide is a modified IL- 15 peptide.

26. The method of any one of claims 21 to 23, wherein the at least one interferon peptide is a gamma interferon peptide.

27. The method of any one of claims 21 to 23, wherein the at least one interferon peptide is an alpha interferon peptide.

28. The method of any one of claims 21 to 23, wherein the at least one interferon peptide is a modified interferon peptide.

29. The method of claim 28, wherein the modified interferon peptide is PEGylated.

30. The method of any one of claims 21 to 29, wherein the at least one peptide is administered intrathecally.

31. The method of any one of claim 21 to 30, wherein the method further comprises administering an immune checkpoint inhibitor to the subject.

32. The method of claim 31, wherein the immune checkpoint inhibitor is an inhibitor of an immune checkpoint protein selected from CTLA-4, PD-1, VISTA, B7-H2, B7-H3, PD- L1, B7-H4, B7-H6, ICOS, HVEM, PD-L2, CD160, gp49B, PIR-B, KIR family receptors, TIM-1, TIM-3, TIM-4, LAG-3, BTLA, SIRPalpha (CD47), CD48, 2B4 (CD244), B7.1, B7.2, ILT-2, ILT-4, TIGIT, HHLA2, butyrophilins, A2aR, and combinations thereof.

33. The method of claim 32, wherein the immune checkpoint inhibitor is an inhibitor of PD-1 or PD-L1.

34. The method of any one of claims 31 to 33, wherein the at least one peptide and the immune checkpoint inhibitor are administered conjointly.

35. The method of any one of claims 21 to 34, wherein the cancer is lung cancer, a breast cancer, a colon cancer, a cervical cancer, a pancreatic cancer, a renal cancer, a stomach cancer, a GI cancer, a liver cancer, a bone cancer, a hematological cancer, a neural tissue cancer, a melanoma, a thyroid cancer, a ovarian cancer, a testicular cancer, a prostate cancer, a cervical cancer, a vaginal cancer, or a bladder cancer.

36. The method of claim 35, wherein the cancer comprises a tumor.

37. The method of claim 36, wherein the tumor is an adenocarcinoma, an adrenal tumor, an anal tumor, a bile duct tumor, a bladder tumor, a bone tumor, a brain/CNS tumor, a breast tumor, a cervical tumor, a colorectal tumor, an endometrial tumor, an esophageal tumor, an Ewing tumor, an eye tumor, a gallbladder tumor, a gastrointestinal, a kidney tumor, a laryngeal or hypopharyngeal tumor, a liver tumor, a lung tumor, a mesothelioma tumor, a multiple myeloma tumor, a muscle tumor, a nasopharyngeal tumor, a neuroblastoma, an oral tumor, an osteosarcoma, an ovarian tumor, a pancreatic tumor, a penile tumor, a pituitary tumor, a primary tumor, a prostate tumor, a retinoblastoma, a Rhabdomyosarcoma, a Sali` vary gland tumor, a soft tissue sarcoma, a melanoma, a metastatic tumor, a basal cell carcinoma, a Merkel cell tumor, a testicular tumor, a thymus tumor, a thyroid tumor, a uterine tumor, a vaginal tumor, a vulvar tumor, or a Wilms tumor.

38. A method of treating or preventing leptomeningeal metastasis in a subject afflicted with cancer, the method comprising administering to the subject IL-12 and/or IL-15.

39. A method of recruiting, proliferating, maturing, activating or increasing the survival of dendritic cells and/or natural killer cells to the meninges of a subject afflicted with cancer, the method comprising administering to the subject to the subject IL-12 and/or IL-