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com

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DNA vaccines: prime time is now

Ebony N Gary and David B Weiner

Recently newer synthetic DNA vaccines have been rapidly virus (ZIKV), Ebola virus (EBOV), and the corona-
advanced to clinical study and have demonstrated an viruses- Middle East respiratory syndrome coronavirus
impressive degree of immune potency and tolerability. (MERS-CoV), severe acute respiratory syndrome coro-
Improvements in DNA delivery over prior needle and syringe navirus 1 and 2 (SARS-CoV-1 and SARS-CoV-2)- among
approaches include jet delivery, gene gun delivery, among many others. An ideal vaccine platform should be simple
others. Among the most effective of these new delivery to deploy, rapid to develop, reproducible, temperature
methods, advanced electroporation (EP), combined with other stable, and consistently manufacturable- thus lowering
advances, induces robust humoral and cellular immunity in costs and development risks while providing an impor-
both preventative as well as therapeutic studies. tant new tool. The synthetic DNA (SynDNA) platform
Advancements in the design of the DNA inserts include leader addresses many of these important goals.
sequence changes, RNA and codon optimizations, improved
insert designs, increased concentrations of DNA, and skin DNA immunogens can be directly designed and opti-
delivery, appear to complement newer delivery strategies. mized from pathogen sequences and synthesized allow-
These advances also provide a framework for the in vivo ing flexibility and speed in preclinical testing with rapid
production of synthetic DNA biologics. In this review, we focus transition to clinical scale up. In vivo expression of the
on recent studies of synthetic DNA vaccines in the clinic for the constructed sequences facilitates rapid screening and
prevention or treatment of infectious diseases with a focus on down selection of potential vaccine candidates. Multiple
adaptive electroporation for delivery, and briefly summarize studies have reported that synDNA allows for the gener-
novel preclinical data advancing the in vivo delivery of DNA- ation of cellular and humoral responses against pathogens
encoded antibody-like biologics. with impact in challenge model systems. Originally intra-
muscular (IM) inoculation and more recently intradermal
Address (ID) delivery using highly concentrated formulations
The Wistar Institute, Philadelphia, PA, United States
have induced consistent immunity in the clinic. Delivery
Corresponding author: methods such as jet delivery, gene gun delivery, nano-
Weiner, David B (dweiner@wistar.org, egary@wistar.org) particle delivery, and others have demonstrated increased
DNA uptake in vivo [1

].
Current Opinion in Immunology 2020, 65:21–27
Adaptive electroporation (EP) [2] which controls the
This review comes from a themed issue on Vaccines energy delivered during in vivo EP improves increases
Edited by Bali Pulendran and Rino Rappuoli transformation efficiency over needle and syringe deliv-
For a complete overview see the Issue and the Editorial ery. Following local injection by needle and syringe
Available online 4th April 2020
plasmid DNA is taken up by a limited number of cells
at the site of injection, where the DNA is transcribed into
https://doi.org/10.1016/j.coi.2020.01.006
mRNA and translated into antigen intracellularly. Adap-
0952-7915/ã 2020 The Author(s). Published by Elsevier Ltd. This is an tive EP increases the initial uptake of plasmid by local
open access article under the CC BY license (http://creativecommons.
cells approximately 500x [3]. This creates a large antigen
org/licenses/by/4.0/).
bolus to drive a more potent immune response. With
adaptive EP most cells in the local field can be transfected
[4

]. Locally transfected antigen-presenting cells (APCs)
Introduction can directly traffic to the regional lymph node (LN) which
Vaccines are among the most important medical inter- is critical to initiating the immune response [5,6]. Trans-
ventions in human history. We are in an era of unprec- lated antigen can be shed exogenously and picked up by
edented scientific advance in vaccine technologies. APCs for cross presentation. Shed exogenous soluble
However, the development of new vaccines faces chal- antigen can drain locally to the regional LN and extra-
lenges. This is due to multiple factors including the high cellular spaces in the local environment allowing for
cost of their development which drives a focus on larger engagement of B cell immunity. Local tissue becomes
markets, slower than optimal time lines for vaccine a protein factory for presentation of antigen on major
advancement to clinical testing, among other complexi- histocompatibility complex-1 (MHC I) or MHC II mole-
ties. One example is the increased occurrence of emerg- cules for re-expansion of LN primed CD8+ T cells
ing and reemerging infections which appear sporadically (cytotoxic T lymphocytes, or CTLs) and CD4+ T cells,
and could benefit greatly from rapid vaccine interven- respectively (Figure 1a). For comprehensive review, see
tions. Examples include Lassa, Powasan virus, ZIKA Ref. [4

]. Since the 900 s DNA plasmids have been

www.sciencedirect.com Current Opinion in Immunology 2020, 65:21–27

22 Vaccines

Figure 1

(a) (b)
DNA Immunization DNA-based immunotherapies
Plasmid
DNA SynDNA bispecifics and
DMAbs

•Synthesized in vivo
•Codelivery of multiple dBiTEs Plasmid
•Easily produced DNA
Transfected cells at the site of injection •Long half-life
present antigens on MHC I and MHCII
molecules, priming CD4+ abd CD8+ T
cells. Soluble antigen primes B cell
immunity

DNA
immunization
Direct transfection of
antigen-presenting cells in
tissue

cancer-specific
CD8+ T cells CD8+ T cell
antigen-specific B Traffic to local LNs
cell and amplification of
antigen-specific •Antigen synthesized in vivo
CD8+ T cell responses •Synthetic consensus immunogen
antigen-specific cancer-specific antigens i.e breaks self-tolerance
CD4+ T cell HPVE6, E7
•Easily produced
•Therapeutic and prophylactic
treatment
Antigen-debot •Multiple antigens in a single
provides plasmid formulation
re-expansion of
LN-primed cells

Infectious Disease Targets Malignant Targets

Current Opinion in Immunology

DNA vaccination and immunotherapy. (a) DNA-encoded antigens are transcribed, translated, and presented on MHC I and II molecules in vivo,
promoting robust anti-target immunity. (b) The 1000X increase in DNA delivery coupled with highly efficient encoded antigen production allow this
local delivery to become a source for production of biologics. Inserts are highly designed to allow for local expression. Multiple publications have
now described how DNA-encoded monoclonal antibodies (DMAbs), bispecific antibodies, and immunogens can be used to target cancer or
infectious diseases.

delivered to tens of thousands of patients by multiple of molecular plasmid encoded IL-12 (pIL-12) and EP
routes, in trials studying numerous vaccine antigen tar- delivery resulted in a dose sparing effect with immunoge-
gets with a highly consistent safety record supporting its nicity superior to vaccines with electroporation, with fewer
further clinical development [7]. doses, demonstrating a dose-sparing effect of the combined
platform. In the vaccine + IL-12 group with EP delivery,
Clinical review of recent DNA vaccines more than 80% of vaccinees had detectable HIV-specific T
Here we discuss recent clinical studies using the cell responses after three immunizations [8

].
SynDNA platform (Figure 2) with a specific focus on
DNA vaccines targeting emerging and re-emerging infec- Venezuelan equine encephalitis virus (VEEV) is a mosquito-
tious diseases and cancers of infectious etiology. borne alphavirus and is a recognized biosafety threat for
humans for which there are no approved vaccines or thera-
More than 2 million new human immunodeficiency virus-1 peutics. Hannaman et al. studied a DNA vaccine targeting
(HIV-1) infections occur annually, highlighting the need the E3-E2-6K-E1 genes of the VEEV subtype IAB envelope
for an effective prophylactic vaccine. In two multicenter, and compared intradermal versus intramuscular electropo-
randomized clinical trials the immunogenicity of synDNA ration (EP) at various doses in a small number of human
constructs encoding HIV-1 clade B gag, pol, and env subjects. In this study high dose intramuscular EP resulted in
proteins (PENNVAX-B DNA vaccine (PV)) alone, or in the development of VEEV neutralizing antibodies in all
combination with plasmid-encoded IL-12 was evaluated subjects while intradermal-EP promoted neutralizing anti-
with (HVTN 080) and without (HVTN 070) intramuscular body at lower levels and in fewer subjects [9]. T cell
EP. The vaccination was safe and well-tolerated. Addition responses were not reported in this study.

Current Opinion in Immunology 2020, 65:21–27 www.sciencedirect.com

 Synthetic DNA vaccines: prime time is approaching Gary and Weiner 23

Figure 2

DNA vaccine encoding HIV-1 clade

B gag, pol, env (PENNVAX-GP) with
DNA vaccine encoding HIV-1 molecular IL-12 induced almost Influenza HA DNA prime via
clade B gag, pol, env 100% vaccine response rate with Biojector jet delivery
(PENNVAX-B) with/without durable responses. ID-EP is as followed by trivalent
Molecular IL-12 is safe and potent as IM-EP with 1/5th dose. inactivated influenza boost
immunogenic. EP and pIL-12 HVTN 098 (ClinicalTrials.gov (IIV3) helathy adults. VRC
Wild-type and 703 (ref. 17)
is dose-sparing. First Identifier: NCT02431767)
JEV-chimeric ZIKV Intradermal EP of SynCone
demonstration that DNA +EP jet-delivered DNA EBOV vaccine promotes
induces responses as potent VEEV DNA vaccine vaccines are safe and cellular and humoral
as viral-vectored vaccines. is safe, well tolerated in adult responses in humans. 18
HVTN 070/080 (ref. 5) immunogenic and volunteers VRC319, monts beach-to-clinic (ref.
well-tolerated in 320 (ref. 13) 16)
human patients
(ref. 9)

2013 2015 2016 2017 2018 2019

DNA vaccine +
pembrolizumab Anti-ZIKV DMAb clinical
First-in-human ZIKV DNA MERS-CoV DNA
HPV E6/E7 DNA promotes anti-tumor trial begins February
vaccine is safe and vaccine phase I trial,
vaccines is safe and responses in prostate 2019 (clinicaltrials.gov
immunogenic in vaccine is safe and
efficacious against cancer patients patients identifier:
humans. 6.5 months immunogenic (ref. 19)
cervical neoplasia in (ref. 21) NCT03831503)
bench-to-clinic (ref. 12)
human patients (ref.
24)
Influenza HA DNA prime via Biojector
jet delivery followed by trivalent
inactivated influenza boost (IIV3) in
adults (ref. 21) and children aged 6-17
years. First US study of a DNA
vaccine in children. VRC 702 (ref. 20)

Current Opinion in Immunology

Selected Recent DNA vaccines in the clinic. All the reported constructs were found to be safe and immunogenic in the clinic. Several of these
have reported clinical impact or outcomes representing important immune readouts.

Zika virus (ZIKV) is a mosquito-borne infectious disease was moved from research program initiation to the clinic in
characterized by fever, rash, conjunctivitis, and malaise. just 6.5 months highlighting the efficiency and speed with
Despite the relatively mild clinical illness, ZIKV infection which a synthetic DNA platform can be brought to bear
during pregnancy is associated with severe congenital birth against an emerging or re-emerging pathogen. The Vaccine
defects such as microcephaly. The first Zika vaccine Research Center (VRC) of the national institutes of health
advanced to the clinic was a synDNA vaccine delivered reported the results of two ZIKV DNA vaccine trials (VRC
by adaptive EP [10–12

]. Tebas et al. evaluated the safety 319 and VRC320) evaluating the safety and immunogenic-
and immunogenicity of a synthetic DNA vaccine targeting ity of DNA plasmids encoding the PrM and E proteins of a
Zika prME, [12

]. In this Phase 1 dose-ranging study ZIKV-Japanese encephalitis virus (JEV) chimera delivered
participants received either 1 or 2 mg of ZIKV DNA at 4 mg doses either 2x or 3x (VRC 319) or native leader like
immunogens delivered by the ID route and CELLEC- ZIKV (VRC320) vaccines vaccinated with 4 mg doses
TRA-EP at 0, 4, and 12 weeks. After the third immuniza- immunized three times at different intervals. In VRC
tion Zika-specific binding antibodies were detected in all 319 GMT average per group was (40–197) and for VRC
participants at average titers of 1/2000 for the 1 mg dose 320 GMT ranged from (28–430). The vaccines induced
group or 1/3000 for the higher dose group) 96% of partici- neutralizing titers using a reporter assay and showed T cell
pants developed Zika-neutralizing antibodies detected via mediated cytokine release [13] and the authors suggest that
U87 neuronal cell assay. Importantly, passive transfer stud- the VRC320 vaccine group developed more consistent
ies where patient serum was given to interferon knockout seroconversion, neutralization, and T cell immunity over
mice (which are susceptible to ZIKV infection) showed that the JEV chimeric Zika vaccine.
sera from vaccinated subjects protected mice from lethal
pathogenic ZIKV challenge [12

]. ZIKV-specific T cells Ebola virus (EBOV) is the causative agent of severe viral
were induced in most subjects. This ZIKV DNA vaccine hemorrhagic disease in humans and non-human primates.

www.sciencedirect.com Current Opinion in Immunology 2020, 65:21–27

24 Vaccines

To date, there have been twenty-nine EBOV outbreaks clinical studies of a jet delivered DNA prime, matched,
with mortality rates reaching up to 90%. Patel et al. trivalent inactivated virus boost influenza vaccine regi-
reported that rapid in vivo protection of mice following men in healthy adult volunteers, and in children. Com-
a single immunization with a synthetic DNA vaccine pared to inactivated virus prime and boost, DNA prime
encoding consensus EBOV glycoproteins (GP) represen- and virus boost induced trended toward greater humoral
tative of EBOV outbreak strains spanning the years from responses including hemagglutinin inhibition (HAI) and
1976 to 2008 against a heterologous mouse-adapted neutralization [20

,21]. These findings collectively dem-
EBOV strain [14]. SynEBOV-GP DNA immunization onstrate the ability to rapidly apply the synthetic DNA
also resulted in 100% protection of macaques from lethal platform in the context of infectious disease or EID, with
EBOV challenge [14]. Importantly in these studies potent immune performance, as well the excellent toler-
determined that a dose-sparing 2-injection regimen ability profile of the platform.
delivered via the recently characterized intradermal-EP
(CELLECTRA-EP) [15] route was 100% protective Immunotherapy for viral diseases
against lethal challenge. These responses were persistent Human papilloma viruses (HPV) are oncogenic viruses
up to one year after immunization with robust recall that infect mucosal surfaces. HPV is responsible for
responses observed at this time point [14]. These prom- almost 5% of all cancer worldwide [22]. Recombinant
ising results supported a first in-human (FIH) clinical HPV particle-based vaccines against specific oncogenic
trial. Two EBOV-GP candidates, INO-4201 encoding a HPVs and two strains of HPV that generate genital warts,
SynconEBOV-GP antigen representative of outbreak have impacted the incidence of HPV infection. However,
strains from 1976 to 2008, and INO 4202 encoding Zaire persons already infected with remain at high risk for a
Makona EBOV-GP from a 2014 outbreak, were evaluated collection of HPV diseases, including cervical cancer,
alone, together, and in combination with DNA-encoded head and neck cancer, anal cancer, vaginal cancer, and
human interleukin-12 (IL-12) delivered by either the IM others HPV-associated cancers. The first-in-human (FIH)
or ID routes using Cellectra EP. Both delivery routes clinical trial was advanced to test the hypothesis that a
induced potent anti-Ebola cellular and humoral immu- synthetic DNA vaccine encoding HPV immunogens for
nity. However, the ID delivery route was dose sparing and modified nuclear oncogenes E6 and E7 from HPV types
promoted more rapid seroconversion (100% seroreactiv- 16 and 18 (two high risk genotypes) would induce CTLs
ity) after 2 immunizations. The simplicity, consistency, that might impact HPV-induced cervical intraepithelial
and tolerability of the ID format appears to exhibit neoplasia (CIN). An initial immunogenicity study [23]
important advantages for vaccine development against reported that the vaccine was highly immunogenic,
emerging and re-emerging pathogens [16

], and could driving antibodies and CTLs in almost all vaccinated
have a supportive role for the current VSV-ZEBOV subjects. A follow-up Phase IIb efficacy trail was subse-
vaccine. quently reported [24

]. The study showed potent induc-
tion of immunity including CD8 T cells that migrated to
The Middle East respiratory syndrome coronavirus the diseased cervical tissue. Overall 49.5% of women in
(MERS-CoV), was first identified in 2012 is responsible this study regressed their disease, while 40.2% regressed
for an outbreak of cases which are clustered in the Arabian and cleared their cervical infection. This is the first
Peninsula. In 2015 the first spread of MERS to a non- therapeutic vaccine to show clinical efficacy against grade
Arabian Peninsula country (Seoul, Korea), generated a 2 and 3 CIN [24

]. Additional study of this approach for
major outbreak. Muthumani et al. reported on the devel- CIN is in progress. This report is also the first treatment
opment of a synthetic DNA vaccine encoding a MERS efficacy data generated for a DNA approach against a
spike protein which induced potent humoral and cell- human disease.
mediated immunity in mice, non-human primates, and
camels and protected vaccinated macaques from MERS The SynDNA platform has the potential to synergize
associated pneumonia following virus challenge [17,18]. A with extant cancer therapy. In the clinic McNeel et al.
phase-I, open-label, single-arm, dose-escalation clinical reported that combination anti-PD-1 immunotherapy
trial was opened at the Walter-Reed Army Institute with a T-cell stimulating DNA vaccine was well-tolerated
for Research Clinical Trials. The vaccine was delivered and promoted antitumor responses [25]. A more recent
by intramuscular injection and CELLECTRA-EP. study by Agarwall et al. tested the adaptive EP delivery of
Seroconversion was detected in 95% of patients. a synHPV vaccine for treatment of HPV positive head and
MERS-CoV-specific T cell responses were detected in neck cancers [26]. This phase Ib/II safety, tolerability,
76% of patients and persisted at 60 days post-final immu- and immunogenicity study reported results of immuno-
nization [19

]. therapy with MEDI0457 (DNA immunotherapy target-
ing HPV16/18 E6/E7 co-delivered with plasmid IL12)
Influenza viruses which undergo antigenic drift and shift delivered by adaptive CELLECTRA-EP. Twenty-two
require new vaccine design annually to curb disease patients with locally advanced, p16+head and neck squa-
spread. Recently the VRC of the NIH published two mous cell carcinoma (HNSCC) received MEDI0457.

Current Opinion in Immunology 2020, 65:21–27 www.sciencedirect.com

 Synthetic DNA vaccines: prime time is approaching Gary and Weiner 25

Overall the treatment was well tolerated. 90% of evalu- antibodies targeting cancer-specific antigens or immuno-
able patients showed elevated antigen-specific T-cell suppressive molecules present on immune cells such as
activity by IFNg ELISpot, and persistent cellular cytotoxic T-lymphocyte-associated protein 4 (CTLA-4)
responses surpassing 100 spot-forming units (SFUs)/106 and programmed cell death-1 (PD-1). Indeed anti-PD-1
peripheral blood mononuclear cells (PBMCs) were noted and CTLA-4 immunotherapy have had success in the clinic
out to 1 year. Induction of HPV-specific CD8+ T cells was and become standard of care cancer treatment approaches
observed in tumors post biopsy. One patient developed [27]. Recent reports have described use of the SynDNA-
metastatic disease and flow-cytometric analyses revealed encoded monoclonal antibody (DMAb) therapy to deliver
induction of HPV16-specific PD-1+ CD8+ T cells that anti-PD-1 [28

] and anti-CTLA-4 [29

] immunotherapy
were not found before MEDI0547. Treatment of this in vivo. Bi-specific antibodies which engage cancer targets
patient with anti-PD-1 therapy resulted in a rapid and and cytotoxic T lymphocytes leading to T cell-mediated
durable complete response. These data demonstrate that killing of cancer cells, are growing in clinical importance.
MEDI0457 can induce clear and durable HPV16/18 The first FDA approved bispecific is Blincyto (Blinatumo-
antigen-specific peripheral and tumor-infiltrating mab), which targets CD19 on B cells for treatment of acute
immune responses that may further benefit patients in lymphoblastic leukemia. Bispecfic drugs are complex to
the context of check point inhibitor (CPI) therapy to produce, can have short half-lives and as such, can be
improve therapeutic outcomes. Interestingly, this group associated with high costs per treatment limiting their
reported a second complete responder in the context development and patient access. Taking into account its
of CPI combination therapy. Additional study of this high local production in tissues, new SynDNA Ig produc-
approach is ongoing (ClinicalTrials.gov Identifier: tion approach offer an alternative production pipeline for
NCT04001413). The combination of CPI with a potent biologics. As an extension of this approach Perales-Puchalt
T cell generating synDNA vaccine represents an impor- reported on in vivo delivery with several months expression
tant tool for additional study in the broader context of of a DNA encoded bispecific antibody delivered directly in
cancer immunotherapy. vivo which demonstrated potent tumor control in a mouse
model [30

] supporting the delivery of nonnative Ig forms.
SynDNA biologics in the preclinical setting
The use of biologics and modified biologics to treat various Early reports described the use of plasmid vector systems
diseases has rapidly expanded. Similarly, other immune for the generation of antibody like molecules as well as anti-
disorders and cancers may be treated with monoclonal HIV-1 envelope neutralizing F(ab)s [31]. Xu et al. reported

Table 1

Selected preclinical studies for DNA-encoded biologics

Target Disease etiology Biologic class Major findings Ref.

Zika virus Infectious DMAb Dual or single plasmid DNA delivery system results in expression of ZIKV [38

]
neutralizing antibodies and serum from DMAb immunized mice, protects naı̈ve
mice from ZIKV lethal challenge.
Ebola virus Infectious DMAb EBOV DMAbs confer 100% protection from lethal challenge in mice/. [35,39]
P. Aeruginosa Infectious DMAb Anti-Pseudomonas DMAB protects mice from lethal pneumonia challenge and [40

]
synergizes with antibiotic therapy resulting in protection from Antibiotic-resistant
pneumonia.
B. burgdorferi Infectious DMAb Anti-Borrelia DMAb protects mice from tick challenge and represents a novel [41]
method for blocking Lyme disease transmission.
HIV-1 Infectious F(ab) Anti-HIV envelope neutralizing VRC01 F(ab) is produced rapidly in vivo following [31]
DNA immunization and EP.
HIV-1 Infectious Broadly Multiple bNAbs expressed in mice and NHPs at high concentration [33

]
neutralizing Abs simultaneously, for extended periods
Dengue Infectious DMAb Delivery of multiple neutralizing DMAbs protects against all DENV serotypes and [36]
prevents antibody-dependent enhancement.
Chikungunya virus Infectious DMAb A single injection of DMAb prophylaxis protects mice from CHIKV challenge. [37

]
Combination of DNA and DMAb immunization affords both rapid and long-term
protection.
Influenza Infectious DMAb DMAbs targeting influenza A and B protect mice from lethal challenge. [34,35]
HIV-1 Infectious Ig-like molecule Proof-of-concept study for DNA-based delivery of anti-HIV immunoadhesins [32

]
and in vivo modulation of protein function.
PD-1 Malignancy DMAb Anti-PD-1 DMAbs are produced rapidly and persist in mouse sera, extending [28

]
therapeutic window of immune checkpoint blockade therapy.
CTLA-4 Malignancy DMAb Anti-CTLA-4 DMAbs are rapidly produced in vivo and shrink tumors in mouse [29

]
cancer models.
HER2 Malignancy DMAb/DBiTE Anti-HER2 DMAb and a bispecific targeting HER2 and CD3 induce control of [30

]
ovarian tumors in mice and prolong survival.

www.sciencedirect.com Current Opinion in Immunology 2020, 65:21–27

26 Vaccines

the use of the synDNA platform to express and sulfate the for consulting. This service includes serving on scientific
antibody-like HIV-1 entry inhibitor eCD4-Ig [32

] illus- review committees and advisory boards. Remuneration
trating the potential for complex in vivo biologic assembly. includes direct payments or stocks/stock options and in
Recently, Wise et al. reported that DMAbs encoding HIV- the interest of disclosure, therefore, he notes potential
specific broadly neutralizing antibodies could produce conflicts associated with this work with, in particular,
functional broadly neutralizing antibodies in mice and Inovio, where he serves on the BOD/SAB, as well as
non-human primates [33

]. This platform continues to with Pfizer, Bristol-Myers Squibb, Merck, Aldevron,
advance and DMAbs targeting influenza A and B Roche, Ferring Pharmaceuticals, and possibly others.
[34,35], dengue [36], Chikungunya [37

], Zika [38

],
and Ebola [35,39] with of protection in animal models.
References and recommended reading
DMAbs may also provide advantages as anti-bacterial ther- Papers of particular interest, published within the period of review,
have been highlighted as
apeutics to complement antibiotics. Patel et al. reported that
an optimized DMAb targeting the bacterium Pseudomonas

of outstanding interest
aeruginosa protected against lethal pneumonia in a mouse
model of antibiotic-resistant P. aeruginosa [40

]. Similarly,
1. Jorritsma S, Gowans E, Grubor-Bauk B, Wijesundara D: Delivery


methods to increase cellular uptake and immunogenicity of
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Borrelia-infected ticks, blocking Lyme disease transmission intramuscular electroporation: providing a “boost” for DNA
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[41]. These recent studies illustrate the growing interest in 3. Lambricht L, Lopes A, Kos S, Sersa G, Préat V, Vandermeulen G:
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borations, and has received speaking honoraria and fees Safety, tolerability, and immunogenicity of two Zika virus DNA

Current Opinion in Immunology 2020, 65:21–27 www.sciencedirect.com

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