A Multiagent Alphavirus DNA Vaccine Delivered by Intramuscular Electroporation Elicits Robust and Durable Virus-Specific Immune Responses in Mice and Rabbits and Completely Protects Mice against Lethal Venezuelan, Western, and Eastern Equine Encephalitis Virus Aerosol Challenges

Syrian Hamsters Model Does Not Reflect Human-like Disease after Aerosol Exposure to Encephalitic Alphaviruses

Venezuelan (VEE), eastern (EEE), and western (WEE) equine encephalitis viruses are encephalitic New World alphaviruses that cause periodic epizootic and epidemic outbreaks in horses and humans that may cause severe morbidity and mortality. Currently there are no FDA-licensed vaccines or effective antiviral therapies. Each year, there are a limited number of human cases of encephalitic alphaviruses; thus, licensure of a vaccine or therapeutic would require approval under the FDA animal rule. Approval under the FDA animal rule requires the disease observed in the animal model to recapitulate what is observed in humans. Currently, initial testing of vaccines and therapeutics is performed in the mouse model. Unfortunately, alphavirus disease manifestations in a mouse do not faithfully recapitulate human disease; the VEEV mouse model is lethal whereas in humans VEEV is rarely lethal. In an effort to identify a more appropriate small animal model, we evaluated hamsters in an aerosol exposure model of encephalitic alphavirus infection. The pathology, lethality, and viremia observed in the infected hamsters was inconsistent with what is observed in NHP models and humans. These data suggest that hamsters are not an appropriate model for encephalitic alphaviruses to test vaccines or potential antiviral therapies.

Designing a Multiepitope Vaccine against Eastern Equine Encephalitis Virus: Immunoinformatics and Computational Approaches

Eastern equine encephalitis virus (EEEV) is a significant threat to human and animal populations, causing severe encephalitis, often leading to long-term neurological complications and even mortality. Despite this, no approved antiviral treatments or EEEV human vaccines currently exist. In response, we utilized immunoinformatics and computational approaches to design a multiepitope vaccine candidate for EEEV. By screening the structural polyprotein of EEEV, we predicted both T-cell and linear B-cell epitopes. These epitopes underwent comprehensive evaluations for their antigenicity, toxicity, and allergenicity. From these evaluations, we selected ten epitopes highly suitable for vaccine design, which were connected with adjuvants using a stable linker. The resulting vaccine construct demonstrated exceptional antigenic, nontoxic, nonallergenic, and physicochemical properties. Subsequently, we employed molecular docking and molecular dynamics simulations to reveal a stable interaction pattern between the vaccine candidate and Toll-like receptor 5. Besides, computational immune simulations predicted the vaccine's capability to induce robust immune responses. Our study addresses the urgent need for effective EEEV preventive strategies and offers valuable insights for EEEV vaccine development. As EEEV poses a severe threat with potential spread due to climate change, our research provides a crucial step in enhancing public health defenses against this menacing zoonotic disease.

Developing a Prototype Pathogen Plan and Research Priorities for the Alphaviruses

The Togaviridae family, genus, Alphavirus, includes several mosquito-borne human pathogens with the potential to spread to near pandemic proportions. Most of these are zoonotic, with spillover infections of humans and domestic animals, but a few such as chikungunya virus (CHIKV) have the ability to use humans as amplification hosts for transmission in urban settings and explosive outbreaks. Most alphaviruses cause nonspecific acute febrile illness, with pathogenesis sometimes leading to either encephalitis or arthralgic manifestations with severe and chronic morbidity and occasional mortality. The development of countermeasures, especially against CHIKV and Venezuelan equine encephalitis virus that are major threats, has included vaccines and antibody-based therapeutics that are likely to also be successful for rapid responses with other members of the family. However, further work with these prototypes and other alphavirus pathogens should target better understanding of human tropism and pathogenesis, more comprehensive identification of cellular receptors and entry, and better understanding of structural mechanisms of neutralization.

A roadmap for developing Venezuelan equine encephalitis virus (VEEV) vaccines: Lessons from the past, strategies for the future

Venezuelan equine encephalitis (VEE) is a zoonotic infectious disease caused by the Venezuelan equine encephalitis virus (VEEV), which can lead to severe central nervous system infections in both humans and animals. At present, the medical community does not possess a viable means of addressing VEE, rendering the prevention of the virus a matter of paramount importance. Regarding the prevention and control of VEEV, the implementation of a vaccination program has been recognized as the most efficient strategy. Nevertheless, there are currently no licensed vaccines or drugs available for human use against VEEV. This imperative has led to a surge of interest in vaccine research, with VEEV being a prime focus for researchers in the field. In this paper, we initially present a comprehensive overview of the current taxonomic classification of VEEV and the cellular infection mechanism of the virus. Subsequently, we provide a detailed introduction of the prominent VEEV vaccine types presently available, including inactivated vaccines, live attenuated vaccines, genetic, and virus-like particle vaccines. Moreover, we emphasize the challenges that current VEEV vaccine development faces and suggest urgent measures that must be taken to overcome these obstacles. Notably, based on our latest research, we propose the feasibility of incorporation codon usage bias strategies to create the novel VEEV vaccine. Finally, we prose several areas that future VEEV vaccine development should focus on. Our objective is to encourage collaboration between the medical and veterinary communities, expedite the translation of existing vaccines from laboratory to clinical applications, while also preparing for future outbreaks of new VEEV variants.

A DNA vaccine targeting VEE virus delivered by needle-free jet-injection protects macaques against aerosol challenge

We have previously shown that DNA vaccines expressing codon optimized alphavirus envelope glycoprotein genes protect both mice and nonhuman primates from viral challenge when delivered by particle-mediated epidermal delivery (PMED) or intramuscular (IM) electroporation (EP). Another technology with fewer logistical drawbacks is disposable syringe jet injection (DSJI) devices developed by PharmaJet, Inc. These needle-free jet injection systems are spring-powered and capable of delivering vaccines either IM or into the dermis (ID). Here, we evaluated the immunogenicity of our Venezuelan equine encephalitis virus (VEEV) DNA vaccine delivered by either the IM- or ID-DSJI devices in nonhuman primates. The protective efficacy was assessed following aerosol challenge. We found that a prime and single boost by either the IM or ID route resulted in humoral and cellular immune responses that provided significant protection against disease and viremia. Although the ID route utilized one-fifth the DNA dose used in the IM route of vaccination, and the measured humoral and cellular immune responses trended lower, the level of protection was high and performed as well as the IM route for several clinical endpoints.

Resurgence of Interest in Eastern Equine Encephalitis Virus Vaccine Development

Eastern equine encephalitis virus (EEEV; Family Togaviridae), is an endemic pathogen first isolated in 1933 with distribution primarily in the eastern US and Canada. The virus has caused periodic outbreaks in both humans and equines along the eastern seaboard and through the southern coastal states. While the outbreaks caused by EEEV have been sporadic and varied geographically since the discovery of the virus, it has continued to expand its range moving into the Midwest states as well. Additionally, one of the largest outbreaks was recorded in 2019 prompting concerns that outbreaks were becoming larger and more frequent. Because the virus can cause serious disease and because it is transmissible by both mosquitoes and aerosol, there has been renewed interest in identifying potential options for vaccines. Currently, there are no licensed vaccines and control relies completely on the use of personal protective measures and integrated vector control which have limited effectiveness for the EEEV vectors. Several vaccine candidates are currently being developed; this review will describe the multiple options under consideration for future development and assess their relative advantages and disadvantages.

Synthesis and biological activity of conformationally restricted indole-based inhibitors of neurotropic alphavirus replication: Generation of a three-dimensional pharmacophore

We have previously reported the development of indole-based CNS-active antivirals for the treatment of neurotropic alphavirus infection, but further optimization is impeded by a lack of knowledge of the molecular target and binding site. Herein we describe the design, synthesis and evaluation of a series of conformationally restricted analogues with the dual objectives of improving potency/selectivity and identifying the most bioactive conformation. Although this campaign was only modestly successful at improving potency, the sharply defined SAR of the rigid analogs enabled the definition of a three-dimensional pharmacophore, which we believe will be of value in further analog design and virtual screening for alternative antiviral leads.

Insights into Antibody-Mediated Alphavirus Immunity and Vaccine Development Landscape

Alphaviruses are mosquito-borne pathogens distributed worldwide in tropical and temperate areas causing a wide range of symptoms ranging from inflammatory arthritis-like manifestations to the induction of encephalitis in humans. Historically, large outbreaks in susceptible populations have been recorded followed by the development of protective long-lasting antibody responses suggesting a potential advantageous role for a vaccine. Although the current understanding of alphavirus antibody-mediated immunity has been mainly gathered in natural and experimental settings of chikungunya virus (CHIKV) infection, little is known about the humoral responses triggered by other emerging alphaviruses. This knowledge is needed to improve serology-based diagnostic tests and the development of highly effective cross-protective vaccines. Here, we review the role of antibody-mediated immunity upon arthritogenic and neurotropic alphavirus infections, and the current research efforts for the development of vaccines as a tool to control future alphavirus outbreaks.

Vaccine Advances against Venezuelan, Eastern, and Western Equine Encephalitis Viruses

Vaccinations are a crucial intervention in combating infectious diseases. The three neurotropic Alphaviruses, Eastern (EEEV), Venezuelan (VEEV), and Western (WEEV) equine encephalitis viruses, are pathogens of interest for animal health, public health, and biological defense. In both equines and humans, these viruses can cause febrile illness that may progress to encephalitis. Currently, there are no licensed treatments or vaccines available for these viruses in humans. Experimental vaccines have shown variable efficacy and may cause severe adverse effects. Here, we outline recent strategies used to generate vaccines against EEEV, VEEV, and WEEV with an emphasis on virus-vectored and plasmid DNA delivery. Despite candidate vaccines protecting against one of the three viruses, few studies have demonstrated an effective trivalent vaccine. We evaluated the potential of published vaccines to generate cross-reactive protective responses by comparing DNA vaccine sequences to a set of EEEV, VEEV, and WEEV genomes and determining the vaccine coverages of potential epitopes. Finally, we discuss future directions in the development of vaccines to combat EEEV, VEEV, and WEEV.

Nanoplasmid Vectors Co-expressing Innate Immune Agonists Enhance DNA Vaccines for Venezuelan Equine Encephalitis Virus and Ebola Virus

DNA vaccines expressing codon-optimized Venezuelan equine encephalitis virus (VEEV) and Ebola virus (EBOV) glycoprotein genes provide protective immunity to mice and nonhuman primates when delivered by intramuscular (IM) electroporation (EP). To achieve equivalent protective efficacy in the absence of EP, we evaluated VEEV and EBOV DNA vaccines constructed using minimalized Nanoplasmid expression vectors that are smaller than conventional plasmids used for DNA vaccination. These vectors may also be designed to co-express type I interferon inducing innate immune agonist genes that have an adjuvant effect. Nanoplasmid vaccinated mice had increased antibody responses as compared to those receiving our conventional pWRG7077-based vaccines when delivered by IM injection, and these responses were further enhanced by the inclusion of the innate immune agonist genes. The Nanoplasmid VEEV DNA vaccines also significantly increased protection against aerosol VEEV challenge as compared to the pWRG7077 VEEV DNA vaccine. Although all mice receiving the pWRG7077 and Nanoplasmid EBOV DNA vaccines at the dose tested survived EBOV challenge, only mice receiving the Nanoplasmid EBOV DNA vaccine that co-expresses the innate immune agonist genes failed to lose weight after challenge. Our results suggest that Nanoplasmid vectors can improve the immunogenicity and protective efficacy of alphavirus and filovirus DNA vaccines.

Aerosol infection of Balb/c mice with eastern equine encephalitis virus; susceptibility and lethality

BACKGROUND

Eastern equine encephalitis virus is an alphavirus that naturally cycles between mosquitoes and birds or rodents in Eastern States of the US. Equine infection occurs by being bitten by cross-feeding mosquitoes, with a case fatality rate of up to 75% in humans during epizootic outbreaks. There are no licensed medical countermeasures, and with an anticipated increase in mortality when exposed by the aerosol route based on anecdotal human data and experimental animal data, it is important to understand the pathogenesis of this disease in pursuit of treatment options. This report details the clinical and pathological findings of mice infected with EEEV by the aerosol route, and use as a model for EEEV infection in humans.

METHODS

Mice were exposed by the aerosol route to a dose range of EEEV to establish the median lethal dose. A pathogenesis study followed whereby mice were exposed to a defined dose of virus and sacrificed at time-points thereafter for histopathological analysis and virology.

RESULTS

Clinical signs of disease appeared within 2 days post challenge, culminating in severe clinical signs within 24 h, neuro-invasion and dose dependent lethality. EEEV was first detected in the lung 1 day post challenge, and by day 3 peak viral titres were observed in the brain, spleen and blood, corresponding with severe meningoencephalitis, indicative of encephalitic disease. Lethality follows severe neurological signs, and may be linked to a threshold level of virus replication in the brain. Effective medical countermeasures for EEEV may necessitate early inoculation to inhibit infection of the brain in zoonotic incidents, and be able to traverse the blood-brain barrier to sufficiently interrupt replication in the brain in cases of aerosol infection.

CONCLUSIONS

There is little human data on the hazard posed by aerosol infection with encephalitic alphaviruses, and use of EEEV as a bioweapon may be by the aerosol route. A well characterized model of aerosol exposure that recapitulates some of the most severe human clinical features is necessary to evaluate the efficacy of putative medical countermeasures, and to increase our understanding about how this route of infection induces such rapid neuro-invasion and resulting disease.

The genetic adjuvant IL-12 enhances the protective efficacy of a DNA vaccine for Venezuelan equine encephalitis virus delivered by intramuscular injection in mice

We have previously shown that DNA vaccines expressing codon-optimized alphavirus envelope glycoprotein genes protect both mice and non-human primates from viral challenge when delivered by intramuscular electroporation (IM-EP). To determine if we could achieve equivalent immunogenicity and protective efficacy in the absence of electroporation, we co-delivered our Venezuelan equine encephalitis virus (VEEV) DNA vaccine with DNA plasmids expressing genetic adjuvants designed to augment immune responses. We tested the T_h1-inducing cytokine IL-12 as well as the granulocyte growth factor GM-CSF, both of which have demonstrated significant adjuvant effect when included in clinical DNA vaccine formulations. Additionally, as multiple reports have described the necessity of IFN-αβ in DNA vaccine immunogenicity, we tested vaccine plasmids encoding a potent stimulator of the IFN-αβ pathway. Our data suggest that IM vaccination of mice with plasmid DNA encoding genetic adjuvants enhances VEEV vaccine immunogenicity, resulting in improved T cell responses, as well as skewing of the anti-VEEV IgG antibody isotype. Additionally, IM vaccination of VEEV DNA vaccine and IL-12 provided complete protection against aerosol VEEV challenge. Overall, our data suggest that co-delivery of genetic adjuvants with alphavirus DNA vaccines using IM delivery can influence the type of immune response obtained and provide comparable protective immunity to that achieved by IM-EP delivery of the vaccine without adjuvants.