Plasmid DNA launches live-attenuated Japanese encephalitis virus and elicits virus-neutralizing antibodies in BALB/c mice

In vivo rescue of arboviruses directly from subgenomic DNA fragments

Reverse genetic systems are mainly used to rescue recombinant viral strains in cell culture. These tools have also been used to generate, by inoculating infectious clones, viral strains directly in living animals. We previously developed the "Infectious Subgenomic Amplicons" (ISA) method, which enables the rescue of single-stranded positive sense RNA viruses in vitro by transfecting overlapping subgenomic DNA fragments. Here, we provide proof-of-concept for direct in vivo generation of infectious particles following the inoculation of subgenomic amplicons. First, we rescued a strain of tick-borne encephalitis virus in mice to transpose the ISA method in vivo. Subgenomic DNA fragments were amplified using a 3-fragment reverse genetics system and inoculated intramuscularly. Almost all animals were infected when quantities of DNA inoculated were at least 20 µg. We then optimized our procedure in order to increase the animal infection rate. This was achieved by adding an electroporation step and/or using a simplified 2- fragment reverse genetics system. Under optimal conditions, a large majority of animals were infected with doses of 20 ng of DNA. Finally, we demonstrated the versatility of this method by applying it to Japanese encephalitis and Chikungunya viruses. This method provides an efficient strategy for in vivo rescue of arboviruses. Furthermore, in the context of the development of DNA-launched live attenuated vaccines, this new approach may facilitate the generation of attenuated strains in vivo. It also enables to deliver a substance free of any vector DNA, which seems to be an important criterion for the development of human vaccines.

Rational design of a DNA-launched live attenuated vaccine against human enterovirus 71

Human Enterovirus 71 (EV71) has emerged as one of the predominant causative agents of hand, foot and mouth disease (HFMD) with global impact. Despite the inactivated vaccine being licensed, other vaccine candidates based on advanced technology platforms are under development. In this report, we rationally designed and constructed two DNA-launched live attenuated vaccine candidates (pDL-EV71) under the control of specific promoters. In vitro and in vivo transfection with pDL-EV71 driven by the CMV promoter successfully yielded fully infectious EV71. More importantly, the administration of pDL-EV71 did not cause clinical symptoms following intracranial or intramuscular inoculation in neonatal and IFNα/βR-/- mice, demonstrating its safety profile. Moreover, a single-dose or two-dose immunization with pDL-EV71 elicited robust neutralizing antibodies against EV71 as well as an antigen-specific cellular response in mice. A single-dose immunization with 10 ​μg of pDL-EV71 conferred complete protection against lethal EV71 infection in neonates born to immunized maternal mice. Overall, our present results demonstrate that pDL-EV71 is a safe and effective vaccine candidate against EV71 for further development.

Single-Dose Immunogenic DNA Vaccines Coding for Live-Attenuated Alpha- and Flaviviruses

Single-dose, immunogenic DNA (iDNA) vaccines coding for whole live-attenuated viruses are reviewed. This platform, sometimes called immunization DNA, has been used for vaccine development for flavi- and alphaviruses. An iDNA vaccine uses plasmid DNA to launch live-attenuated virus vaccines in vitro or in vivo. When iDNA is injected into mammalian cells in vitro or in vivo, the RNA genome of an attenuated virus is transcribed, which starts replication of a defined, live-attenuated vaccine virus in cell culture or the cells of a vaccine recipient. In the latter case, an immune response to the live virus vaccine is elicited, which protects against the pathogenic virus. Unlike other nucleic acid vaccines, such as mRNA and standard DNA vaccines, iDNA vaccines elicit protection with a single dose, thus providing major improvement to epidemic preparedness. Still, iDNA vaccines retain the advantages of other nucleic acid vaccines. In summary, the iDNA platform combines the advantages of reverse genetics and DNA immunization with the high immunogenicity of live-attenuated vaccines, resulting in enhanced safety and immunogenicity. This vaccine platform has expanded the field of genetic DNA and RNA vaccines with a novel type of immunogenic DNA vaccines that encode entire live-attenuated viruses.

Protective Immune Responses Induced by an mRNA-LNP Vaccine Encoding prM-E Proteins against Japanese Encephalitis Virus Infection

Japanese encephalitis virus (JEV) is an important zoonotic pathogen, which causes central nervous system symptoms in humans and reproductive disorders in swine. It has led to severe impacts on human health and the swine industry; however, there is no medicine available for treating yet. Therefore, vaccination is the best preventive measure for this disease. In the study, a modified mRNA vaccine expressing the prM and E proteins of the JEV P3 strain was manufactured, and a mouse model was used to assess its efficacy. The mRNA encoding prM and E proteins showed a high level of protein expression in vitro and were encapsulated into a lipid nanoparticle (LNP). Effective neutralizing antibodies and CD8+ T-lymphocytes-mediated immune responses were observed in vaccinated mice. Furthermore, the modified mRNA can protect mice from a lethal challenge with JEV and reduce neuroinflammation caused by JEV. This study provides a new option for the JE vaccine and lays a foundation for the subsequent development of a more efficient and safer JEV mRNA vaccine.

Live-Attenuated VEEV Vaccine Delivered by iDNA Using Microneedles Is Immunogenic in Rabbits

Effective and simple delivery of DNA vaccines remains a key to successful clinical applications. Previously, we developed a novel class of DNA vaccines, sometimes called iDNA, which encodes the whole live-attenuated vaccine viruses. Compared to a standard DNA vaccine, an iDNA vaccine required a low dose to launch a live-attenuated vaccine in vitro or in vivo. The goal of this pilot study was to investigate if iDNA vaccine encoding live-attenuated Venezuelan equine encephalitis virus (VEEV) can be efficiently delivered in vivo by a microneedle device using a single-dose vaccination with naked iDNA plasmid. For this purpose, we used pMG4020 plasmid encoding live-attenuated V4020 vaccine of VEE virus. The V4020 virus contains structural gene rearrangement, as well as attenuating mutations genetically engineered to prevent reversion mutations. The pMG4020 was administered to experimental rabbits by using a hollow microstructured transdermal system (hMTS) microneedle device. No adverse events to vaccination were noted. Animals that received pMG4020 plasmid have successfully seroconverted, with high plaque reduction neutralization test (PRNT) antibody titers, similar to those observed in animals that received V4020 virus in place of the pMG4020 iDNA plasmid. We conclude that naked iDNA vaccine can be successfully delivered in vivo by using a single-dose vaccination with a microneedle device.

Infectious RNA vaccine protects mice against chikungunya virus infection

We describe a novel vaccine platform that can generate protective immunity to chikungunya virus (CHIKV) in C57BL/6J mice after a single immunization by employing an infectious RNA (iRNA), which upon introduction into a host cell launches an infectious attenuated virus. We and others have previously reported that an engineered deletion of 183 nucleotides in the nsP3 gene attenuates chikungunya virus (CHIKV) and reduces in vivo viral replication and viremia after challenge in mice, macaques and man. Here, we demonstrated that in vitro transfection of iRNA carrying the nsP3 deletion generated infectious viruses, and after intramuscular injection, the iRNA induced robust antibody responses in mice. The iRNA was superior at eliciting binding and neutralizing antibody responses as compared to a DNA vaccine encoding the same RNA (iDNA) or a non-propagating RNA replicon (RREP) lacking the capsid encoding gene. Subsequent challenge with a high dose of CHIKV demonstrated that the antibody responses induced by this vaccine candidate protected animals from viremia. The iRNA approach constitutes a novel vaccine platform with the potential to impact the spread of CHIKV. Moreover, we believe that this approach is likely applicable also to other positive-strand viruses.

Construction and Immunogenicity of Recombinant Vaccinia Virus Vaccine Against Japanese Encephalitis and Chikungunya Viruses Infection in Mice

Japanese encephalitis virus (JEV) is recognized as a public health risk by the World Health Organization. In Asia, each year, ∼70,000 people become infected with JEV, which results in ∼10,000 deaths. Chikungunya virus (CHIKV) is an RNA virus, whose infection mainly causes fever, myalgia, and skin rash. Although the mortality rate is low, it seriously affects daily life. JEV and CHIKV infect humans through mosquitoes; therefore, a recombinant vaccinia virus coexpressing JEV E and CHIKV E1 proteins was constructed to prevent their concurrent infection. In this study, after mice first immunization, booster immunization was performed at 21 days postimmunization (dpi). At 35 dpi, mice were challenged with JEV and CHIKV. Specific antibodies significantly increased in the rVTT-CE1-JE-EGFP group, which were significantly (p < 0.01) higher than those of the control groups at 35 dpi. The plaque reduction neutralization tests (JEV) of rVTT-CE1-JE-EGFP group was 1:320 at 35 dpi. Furthermore, cytokine levels and the percentage of CD3⁺CD4⁺ and CD3⁺CD8⁺ T-lymphocytes in the rVTT-CE1-JE-EGFP group were significantly (p < 0.01) higher than those in the control groups at 35 dpi. After challenge, mice body weights in rVTT-CE1-JE-EGFP group were not significantly altered, and the survival rate was 100%. These results showed the rVTT-CE1-JE-EGFP group elicited significant humoral and cellular immune responses, thus indicating that the recombinant vaccine may serve as a candidate for effective prevention of CHIKV and JEV infection.

Venezuelan equine encephalitis vaccine with rearranged genome resists reversion and protects non-human primates from viremia after aerosol challenge

Live-attenuated V4020 vaccine for Venezuelan equine encephalitis virus (VEEV) containing attenuating rearrangement of the virus structural genes was evaluated in a non-human primate model for immunogenicity and protective efficacy against aerosol challenge with wild-type VEEV. The genomic RNA of V4020 vaccine virus was encoded in the pMG4020 plasmid under control of the CMV promoter and contained the capsid gene downstream from the glycoprotein genes. It also included attenuating mutations from the VEE TC83 vaccine, with E2-120Arg substitution genetically engineered to prevent reversion mutations. The population of V4020 vaccine virus derived from pMG4020-transfected Vero cells was characterized by next generation sequencing (NGS) and indicated no detectable genetic reversions. Cynomolgus macaques were vaccinated with V4020 vaccine virus. After one or two vaccinations including by intramuscular route, high levels of virus-neutralizing antibodies were confirmed with no viremia or apparent adverse reactions to vaccinations. The protective effect of vaccination was evaluated using an aerosol challenge with VEEV. After challenge, macaques had no detectable viremia, demonstrating a protective effect of vaccination with live V4020 VEEV vaccine.

Genetic stability of live-attenuated Zika vaccine candidates

Zika virus (ZIKV) has drawn global attention as the etiologic agent of Zika Congenital Syndrome in babies born to infected pregnant women. To prevent future ZIKV outbreaks and protect persons at risk for severe disease, we developed two live-attenuated vaccine (LAV) candidates containing 10- or 20-nucleotide deletions in the 3'UTR of the viral genome (Δ10 and Δ20). After a single-dose immunization, both Δ10 and Δ20 LAVs protected mice and non-human primates against ZIKV infection. Here, we characterized the stability, safety, and efficacy of the LAVs after continuously culturing them on manufacture Vero cells for ten rounds. Whole genome sequencing showed that passage 10 (P10) LAVs retained the engineered Δ10 and Δ20 deletions; one to four additional mutations emerged at different regions of the genome. In A129 mice, the P10 LAVs exhibited viremia higher than the un-passaged LAVs, but lower than wild-type ZIKV; unlike wild-type ZIKV-infected mice, none of the P10 LAV-infected mice developed disease or death, demonstrating that the P10 LAVs remained attenuated. Mice immunized with a single dose of the P10 LAVs developed robust neutralizing antibody titers (1/1,000 to 1/10,000) and were protected against epidemic ZIKV challenge. The P10 LAVs did not exhibit increased neurovirulence. Intracranial inoculation of one-day-old CD1 pups with 10³ focus-forming units of the P10 Δ10 and Δ20 LAVs resulted in 100% and ≥80% survival, respectively. Furthermore, the P10 LAVs remained incompetent in infecting Aedes aegypti mosquitoes after intrathoracic microinjection. Our results support the phenotypic stability and further development of these promising LAVs for ZIKV.

Novel DNA-launched Venezuelan equine encephalitis virus vaccine with rearranged genome

Novel live-attenuated V4020 vaccine was prepared for Venezuelan equine encephalitis virus (VEEV), an alphavirus from the Togaviridae family. The genome of V4020 virus was rearranged, with the capsid gene expressed using a duplicate subgenomic promoter downstream from the glycoprotein genes. V4020 also included both attenuating mutations from the TC83 VEEV vaccine secured by mutagenesis to prevent reversion mutations. The full-length infectious RNA of V4020 vaccine virus was expressed from pMG4020 plasmid downstream from the CMV promoter and launched replication of live-attenuated V4020 in vitro or in vivo. BALB/c mice vaccinated with a single dose of V4020 virus or with pMG4020 plasmid had no adverse reactions to vaccinations and developed high titers of neutralizing antibodies. After challenge with the wild type VEEV, vaccinated mice survived with no morbidity, while all unvaccinated controls succumbed to lethal infection. Intracranial injections in mice showed attenuated replication of V4020 vaccine virus as compared to the TC83. We conclude that V4020 vaccine has safety advantage over TC83, while provides equivalent protection in a mouse VEEV challenge model.

A single-dose plasmid-launched live-attenuated Zika vaccine induces protective immunity

BACKGROUND

Vaccines are the most effective means to fight and eradicate infectious diseases. Live-attenuated vaccines (LAV) usually have the advantages of single dose, rapid onset of immunity, and durable protection. DNA vaccines have the advantages of chemical stability, ease of production, and no cold chain requirement. The ability to combine the strengths of LAV and DNA vaccines may transform future vaccine development by eliminating cold chain and cell culture with the potential for adventitious agents.

METHODS

A DNA-launched LAV was developed for ZIKV virus (ZIKV), a pathogen that recently caused a global public health emergency. The cDNA copy of a ZIKV LAV genome was engineered into a DNA plasmid. The DNA-LAV plasmid was delivered into mice using a clinically proven device TriGrid™ to launch the replication of LAV.

FINDINGS

A single-dose immunization as low as 0.5 μg of DNA-LAV plasmid conferred 100% seroconversion in A129 mice. All seroconverted mice developed sterilizing immunity, as indicated by no detectable infectious viruses and no increase of neutralizing antibody titers after ZIKV challenge. The immunization also elicited robust T cell responses. In pregnant mice, the DNA-LAV vaccination fully protected against ZIKV-induced disease and maternal-to-fetal transmission. High levels of neutralizing activities were detected in fetal serum, indicating maternal-to-fetal humoral transfer. In male mice, a single-dose vaccination completely prevented testis infection, injury, and oligospermia.

INTERPRETATION

The remarkable simplicity and potency of ZIKV DNA-LAV warrant further development of this vaccine candidate. The DNA-LAV approach may serve as a universal vaccine platform for other plus-sense RNA viruses. FUND: National Institute of Health, Kleberg Foundation, Centers for Disease Control and Prevention, University of Texas Medical Branch.

Sensitive detection of Japanese encephalitis virus by surface molecularly imprinted technique based on fluorescent method

A fluorescence method was used to detect Japanese encephalitis virus using surface molecularly imprinted technique. This method could selectively detect Japanese encephalitis virus with a picomolar detection limit.