Improved mucosal protection against Venezuelan equine encephalitis virus is induced by the molecularly defined, live-attenuated V3526 vaccine candidate

Venezuelan Equine Encephalitis Virus V3526 Vaccine RNA-Dependent RNA Polymerase Mutants Increase Vaccine Safety Through Restricted Tissue Tropism in a Murine Model

BACKGROUND

Venezuelan equine encephalitis virus (VEEV) is an arbovirus endemic to the Americas. There are no approved vaccines or antivirals. TC-83 and V3526 are the best-characterized vaccine candidates for VEEV. Both are live-attenuated vaccines and have been associated with safety concerns, albeit less so for V3526. A previous attempt to improve the TC-83 vaccine focused on further attenuating the vaccine by adding mutations that altered the error incorporation rate of the RNA-dependent RNA polymerase (RdRp).

METHODS

The research presented here examines the impact of these RdRp mutations in V3526 by cloning the 3X and 4X strains, assessing vaccine efficacy against challenge in adult female CD-1 mice, examining neutralizing antibody titers, investigating vaccine tissue tropism, and testing the stability of the mutant strains.

RESULTS

Our results show that the V3526 RdRp mutants exhibited reduced tissue tropism in the spleen and kidney compared to wild-type V3526, while maintaining vaccine efficacy. Illumina sequencing showed that the RdRp mutations could revert to wild-type V3526.

CONCLUSIONS

The observed genotypic reversion is likely of limited concern because wild-type V3526 is still an effective vaccine capable of providing protection. Our results indicate that the V3526 RdRp mutants may be a safer vaccine design than the original V3526.

Approach to Strain Selection and the Propagation of Viral Stocks for Venezuelan Equine Encephalitis Virus Vaccine Efficacy Testing under the Animal Rule

Licensure of a vaccine to protect against aerosolized Venezuelan equine encephalitis virus (VEEV) requires use of the U.S. Food and Drug Administration (FDA) Animal Rule to assess vaccine efficacy as human studies are not feasible or ethical. An approach to selecting VEEV challenge strains for use under the Animal Rule was developed, taking into account Department of Defense (DOD) vaccine requirements, FDA Animal Rule guidelines, strain availability, and lessons learned from the generation of filovirus challenge agents within the Filovirus Animal Nonclinical Group (FANG). Initial down-selection to VEEV IAB and IC epizootic varieties was based on the DOD objective for vaccine protection in a bioterrorism event. The subsequent down-selection of VEEV IAB and IC isolates was based on isolate availability, origin, virulence, culture and animal passage history, known disease progression in animal models, relevancy to human disease, and ability to generate sufficient challenge material. Methods for the propagation of viral stocks (use of uncloned (wild-type), plaque-cloned, versus cDNA-cloned virus) to minimize variability in the potency of the resulting challenge materials were also reviewed. The presented processes for VEEV strain selection and the propagation of viral stocks may serve as a template for animal model development product testing under the Animal Rule to other viral vaccine programs. This manuscript is based on the culmination of work presented at the “Alphavirus Workshop” organized and hosted by the Joint Vaccine Acquisition Program (JVAP) on 15 December 2014 at Fort Detrick, Maryland, USA.

T Lymphocytes as Measurable Targets of Protection and Vaccination Against Viral Disorders

Continuous epidemiological surveillance of existing and emerging viruses and their associated disorders is gaining importance in light of their abilities to cause unpredictable outbreaks as a result of increased travel and vaccination choices by steadily growing and aging populations. Close surveillance of outbreaks and herd immunity are also at the forefront, even in industrialized countries, where previously eradicated viruses are now at risk of re-emergence due to instances of strain recombination, contractions in viral vector geographies, and from their potential use as agents of bioterrorism. There is a great need for the rational design of current and future vaccines targeting viruses, with a strong focus on vaccine targeting of adaptive immune effector memory T cells as the gold standard of immunity conferring long-lived protection against a wide variety of pathogens and malignancies. Here, we review viruses that have historically caused large outbreaks and severe lethal disorders, including respiratory, gastric, skin, hepatic, neurologic, and hemorrhagic fevers. To observe trends in vaccinology against these viral disorders, we describe viral genetic, replication, transmission, and tropism, host-immune evasion strategies, and the epidemiology and health risks of their associated syndromes. We focus on immunity generated against both natural infection and vaccination, where a steady shift in conferred vaccination immunogenicity is observed from quantifying activated and proliferating, long-lived effector memory T cell subsets, as the prominent biomarkers of long-term immunity against viruses and their associated disorders causing high morbidity and mortality rates.

Alphavirus-Based Vaccines

Alphavirus-based vectors have been engineered from Semliki Forest virus, Sindbis virus, and Venezuelan equine encephalitis virus and applied for vaccine development. Immunization in preclinical animal models has been conducted with naked RNA replicons, recombinant viral particles and layered DNA-RNA vectors. Most commonly, the targets for the immunization have been viral surface proteins and tumor antigens, which have elicited strong immune responses and even provided protection against challenges with lethal doses of virus and tumor cells, respectively. As alphaviruses also cause epidemics, vaccines have been developed against Chikungunya virus. Despite the success in several animal smodels only a few clinical trials have been conducted in humans, so far.

Live, Attenuated Venezuelan Equine Encephalitis Virus Vaccine (TC83) Causes Persistent Brain Infection in Mice with Non-functional αβ T-Cells

Intranasal infection with vaccine strain of Venezuelan equine encephalitis virus (TC83) caused persistent viral infection in the brains of mice without functional αβ T-cells (αβ-TCR -/-). Remarkably, viral kinetics, host response gene transcripts and symptomatic disease are similar between αβ-TCR -/- and wild-type C57BL/6 (WT) mice during acute phase of infection [0-13 days post-infection (dpi)]. While WT mice clear infectious virus in the brain by 13 dpi, αβ-TCR -/- maintain infectious virus in the brain to 92 dpi. Persistent brain infection in αβ-TCR -/- correlated with inflammatory infiltrates and elevated cytokine protein levels in the brain at later time points. Persistent brain infection of αβ-TCR -/- mice provides a novel model to study prolonged alphaviral infection as well as the effects and biomarkers of long-term viral inflammation in the brain.

Characterization of a Pathogenic Full-Length cDNA Clone and Transmission Model for Porcine Epidemic Diarrhea Virus Strain PC22A

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic alphacoronavirus. In the United States, highly virulent PEDV strains cause between 80 and 100% mortality in suckling piglets and are rapidly transmitted between animals and farms. To study the genetic factors that regulate pathogenesis and transmission, we developed a molecular clone of PEDV strain PC22A. The infectious-clone-derived PEDV (icPEDV) replicated as efficiently as the parental virus in cell culture and in pigs, resulting in lethal disease in vivo. Importantly, recombinant PEDV was rapidly transmitted to uninoculated pigs via indirect contact, demonstrating virulence and efficient transmission while replicating phenotypes seen in the wild-type virus. Using reverse genetics, we removed open reading frame 3 (ORF3) and replaced this region with a red fluorescent protein (RFP) gene to generate icPEDV-ΔORF3-RFP. icPEDV-ΔORF3-RFP replicated efficiently in vitro and in vivo, was efficiently transmitted among pigs, and produced lethal disease outcomes. However, the diarrheic scores in icPEDV-ΔORF3-RFP-infected pigs were lower than those in wild-type-virus- or icPEDV-infected pigs, and the virus formed smaller plaques than those of PC22A. Together, these data describe the development of a robust reverse-genetics platform for identifying genetic factors that regulate pathogenic outcomes and transmission efficiency in vivo, providing key infrastructural developments for developing and evaluating the efficacy of live attenuated vaccines and therapeutics in a clinical setting.

IMPORTANCE

Porcine epidemic diarrhea virus (PEDV) emerged in the United States in 2013 and has since killed 10% of U.S. farm pigs. Though the disease has been circulating internationally for decades, the lack of a rapid reverse-genetics platform for manipulating PEDV and identifying genetic factors that impact transmission and virulence has hindered the study of this important agricultural disease. Here, we present a DNA-based infectious-clone system that replicates the pathogenesis of circulating U.S. strain PC22A both in vitro and in piglets. This infectious clone can be used both to study the genetics, virulence, and transmission of PEDV coronavirus and to inform the creation of a live attenuated PEDV vaccine.

Alphavirus-Based Vaccines

Alphavirus vectors based on Semliki Forest virus, Sindbis virus, and Venezuelan equine encephalitis virus have been widely applied for vaccine development. Naked RNA replicons, recombinant viral particles, and layered DNA vectors have been subjected to immunization in preclinical animal models with antigens for viral targets and tumor antigens. Moreover, a limited number of clinical trials have been conducted in humans. Vaccination with alphavirus vectors has demonstrated efficient immune responses and has showed protection against challenges with lethal doses of virus and tumor cells, respectively. Moreover, vaccines have been developed against alphaviruses causing epidemics such as Chikungunya virus.

Self-replicating alphavirus RNA vaccines

Recombinant nucleic acids are considered as promising next-generation vaccines. These vaccines express the native antigen upon delivery into tissue, thus mimicking live attenuated vaccines without having the risk of reversion to pathogenicity. They also stimulate the innate immune system, thus potentiating responses. Nucleic acid vaccines are easy to produce at reasonable cost and are stable. During the past years, focus has been on the use of plasmid DNA for vaccination. Now mRNA and replicon vaccines have come into focus as promising technology platforms for vaccine development. This review discusses self-replicating RNA vaccines developed from alphavirus expression vectors. These replicon vaccines can be delivered as RNA, DNA or as recombinant virus particles. All three platforms have been pre-clinically evaluated as vaccines against a number of infectious diseases and cancer. Results have been very encouraging and propelled the first human clinical trials, the results of which have been promising.

RNA-based drugs and vaccines

RNA-based approaches have provided novel alternatives for modern drug discovery. The application of RNA as therapeutic agents has, until recently, been hampered by issues related to poor delivery and stability, but chemical modifications and new delivery approaches have increased progress. Moreover, the discovery of the importance of RNA in gene regulation and gene silencing has revealed new drug targets, especially related to treatment of cancer and other diseases. Recent engineering of small molecules designed from RNA sequences to target miRNAs opens up new possibilities in drug development. Furthermore, RNA-based vaccines have been engineered applying RNA virus vectors and non-viral delivery for vaccine development.

Combined alphavirus replicon particle vaccine induces durable and cross-protective immune responses against equine encephalitis viruses

Alphavirus replicons were evaluated as potential vaccine candidates for Venezuelan equine encephalitis virus (VEEV), western equine encephalitis virus (WEEV), or eastern equine encephalitis virus (EEEV) when given individually or in combination (V/W/E) to mice or cynomolgus macaques. Individual replicon vaccines or the combination V/W/E replicon vaccine elicited strong neutralizing antibodies in mice to their respective alphavirus. Protection from either subcutaneous or aerosol challenge with VEEV, WEEV, or EEEV was demonstrated out to 12 months after vaccination in mice. Individual replicon vaccines or the combination V/W/E replicon vaccine elicited strong neutralizing antibodies in macaques and demonstrated good protection against aerosol challenge with an epizootic VEEV-IAB virus, Trinidad donkey. Similarly, the EEEV replicon and V/W/E combination vaccine elicited neutralizing antibodies against EEEV and protected against aerosol exposure to a North American variety of EEEV. Both the WEEV replicon and combination V/W/E vaccination, however, elicited poor neutralizing antibodies to WEEV in macaques, and the protection conferred was not as strong. These results demonstrate that a combination V/W/E vaccine is possible for protection against aerosol challenge and that cross-interference between the vaccines is minimal. Importance: Three related viruses belonging to the genus Alphavirus cause severe encephalitis in humans: Venezuelan equine encephalitis virus (VEEV), western equine encephalitis virus (WEEV), and eastern equine encephalitis virus (EEEV). Normally transmitted by mosquitoes, these viruses can cause disease when inhaled, so there is concern that these viruses could be used as biological weapons. Prior reports have suggested that vaccines for these three viruses might interfere with one another. We have developed a combined vaccine for Venezuelan equine encephalitis, western equine encephalitis, and eastern equine encephalitis expressing the surface proteins of all three viruses. In this report we demonstrate in both mice and macaques that this combined vaccine is safe, generates a strong immune response, and protects against aerosol challenge with the viruses that cause Venezuelan equine encephalitis, western equine encephalitis, and eastern equine encephalitis.

Second generation inactivated eastern equine encephalitis virus vaccine candidates protect mice against a lethal aerosol challenge

Currently, there are no FDA-licensed vaccines or therapeutics for eastern equine encephalitis virus (EEEV) for human use. We recently developed several methods to inactivate CVEV1219, a chimeric live-attenuated eastern equine encephalitis virus (EEEV). Dosage and schedule studies were conducted to evaluate the immunogenicity and protective efficacy of three potential second-generation inactivated EEEV (iEEEV) vaccine candidates in mice: formalin-inactivated CVEV1219 (fCVEV1219), INA-inactivated CVEV1219 (iCVEV1219) and gamma-irradiated CVEV1219 (gCVEV1219). Both fCVEV1219 and gCVEV1219 provided partial to complete protection against an aerosol challenge when administered by different routes and schedules at various doses, while iCVEV1219 was unable to provide substantial protection against an aerosol challenge by any route, dose, or schedule tested. When evaluating antibody responses, neutralizing antibody, not virus specific IgG or IgA, was the best correlate of protection. The results of these studies suggest that both fCVEV1219 and gCVEV1219 should be evaluated further and considered for advancement as potential second-generation inactivated vaccine candidates for EEEV.

Alphavirus-based vaccines

Alphavirus vectors have demonstrated high levels of transient heterologous gene expression both in vitro and in vivo and, therefore, possess attractive features for vaccine development. The most commonly used delivery vectors are based on three single-stranded encapsulated alphaviruses, namely Semliki Forest virus, Sindbis virus and Venezuelan equine encephalitis virus. Alphavirus vectors have been applied as replication-deficient recombinant viral particles and, more recently, as replication-proficient particles. Moreover, in vitro transcribed RNA, as well as layered DNA vectors have been applied for immunization. A large number of highly immunogenic viral structural proteins expressed from alphavirus vectors have elicited strong neutralizing antibody responses in multispecies animal models. Furthermore, immunization studies have demonstrated robust protection against challenges with lethal doses of virus in rodents and primates. Similarly, vaccination with alphavirus vectors expressing tumor antigens resulted in prophylactic protection against challenges with tumor-inducing cancerous cells. As certain alphaviruses, such as Chikungunya virus, have been associated with epidemics in animals and humans, attention has also been paid to the development of vaccines against alphaviruses themselves. Recent progress in alphavirus vector development and vaccine technology has allowed conducting clinical trials in humans.

Human norovirus detection and production, quantification, and storage of virus-like particles

Human noroviruses constitute a significant worldwide disease burden. Each year, noroviruses cause over 267 million infections, deaths in over 200,000 children under the age of five, and over 50% of U.S. food-borne illness. Due to the absence of a tissue culture model or small animal model to study human norovirus, virus-like particles (VLPs) and ELISA-based biological assays have been used to answer questions about norovirus evolution and immunity as well to provide a potential vaccine platform. This chapter outlines the protocols for norovirus detection in stool, as well as norovirus VLP design, production, purification, and storage using a Venezuelan equine encephalitis virus (VEE)-based virus replicon particle (VRP) expression system.

IRES-based Venezuelan equine encephalitis vaccine candidate elicits protective immunity in mice

Venezuelan equine encephalitis virus (VEEV) is an arbovirus that causes periodic outbreaks that impact equine and human populations in the Americas. One of the VEEV subtypes located in Mexico and Central America (IE) has recently been recognized as an important cause of equine disease and death, and human exposure also appears to be widespread. Here, we describe the use of an Internal Ribosome Entry Site (IRES) from encephalomyocarditis virus to stably attenuate VEEV, creating a vaccine candidate independent of unstable point mutations. Mice infected with this virus produced antibodies and were protected against lethal VEEV challenge. This IRES-based vaccine was unable to establish productive infection in mosquito cell cultures or in intrathoracically injected Aedes taeniorhynchus, demonstrating that it cannot be transmitted from a vaccinee. These attenuation, efficacy and safety results justify further development for humans or equids of this new VEEV vaccine candidate.

Human arboviral encephalitis

Worldwide, arboviral illnesses constitute the most important international infectious threat to human neurological health and welfare. Before the availability of effective immunizations, approximately 50,000 cases of Japanese encephalitis occurred in the world each year, one-fifth of which cases proved lethal and a much larger number were left with severe neurological handicaps. With global climate change and perhaps other factors, the prevalences of some arboviral illnesses appear to be increasing. Arboviral illnesses, including Japanese encephalitis, tick-borne encephalitis, Yellow fever, and others, are emerging as possible global health care threats because of biological warfare. This chapter will review ecology, pathophysiology, diagnosis, management, and outcome of the forms of arboviral encephalitis that are of greatest importance in North America, together with some of the most important arboviral encephalitides prevalent in other parts of the world.

Venezuelan equine encephalitis in a teenager visiting Central America

BACKGROUND

Stupor, coma, and other alterations of consciousness are among the most serious life-threatening emergencies faced by the emergency department physician. When a patient arrives with altered mentation from Central or South America, the usual causes that occur in the United States must be considered; however, other unusual tropical disease must be excluded, such as Venezuelan equine encephalitis (VEE).

OBJECTIVE

This study aimed to review the clinical features of VEE.

CASE

A 17-year-old female traveled to Belize and developed vomiting, diarrhea, fever, headaches, and myalgias. Over the next few hours, she became disoriented and had a generalized seizure. She was given diazepam, 50% dextrose, phenytoin, mannitol, and vitamin K. A computed tomographic scan of the head was unremarkable. Her parents arranged for a medical air transport. After eliminating other possibilities, she was diagnosed with VEE, which was confirmed in the laboratory. Over the next week, her mental status improved back to her normal neurologic baseline.

CONCLUSIONS

Venezuelan equine encephalitis is an acute viral disease that causes acute illness in equines and humans, with symptoms ranging from a mild, flu-like syndrome to encephalitis or death. Laboratory abnormalities are common and include elevated hepatic transaminases, lymphocytosis, eosinophilia, and thrombocytopenia. Treatment is supportive, and complete recovery is expected within several weeks in most patients.

Arbovirus vaccines; opportunities for the baculovirus-insect cell expression system

The baculovirus-insect cell expression system is a well-established technology for the production of heterologous viral (glyco)proteins in cultured cells, applicable for basic scientific research as well as for the development and production of vaccines and diagnostics. Arboviruses form an emerging group of medically important viral pathogens that are transmitted to humans and animals via arthropod vectors, mostly mosquitoes, ticks or midges. Few arboviral vaccines are currently available, but there is a growing need for safe and effective vaccines against some highly pathogenic arboviruses such as Chikungunya, dengue, West Nile, Rift Valley fever and Bluetongue viruses. This comprehensive review discusses the biology and current state of the art in vaccine development for arboviruses belonging to the families Togaviridae, Flaviviridae, Bunyaviridae and Reoviridae and the potential of the baculovirus-insect cell expression system for vaccine antigen production The members of three of these four arbovirus families have enveloped virions and display immunodominant glycoproteins with a complex structure at their surface. Baculovirus expression of viral antigens often leads to correctly folded and processed (glyco)proteins able to induce protective immunity in animal models and humans. As arboviruses occupy a unique position in the virosphere in that they also actively replicate in arthropod cells, the baculovirus-insect cell expression system is well suited to produce arboviral proteins with correct folding and post-translational processing. The opportunities for recombinant baculoviruses to aid in the development of safe and effective subunit and virus-like particle vaccines against arboviral diseases are discussed.

Treatment of mice with human monoclonal antibody 24h after lethal aerosol challenge with virulent Venezuelan equine encephalitis virus prevents disease but not infection

We recently described a Venezuelan equine encephalitis virus (VEEV)-specific human monoclonal antibody (MAb), F5 nIgG, that recognizes a new neutralization epitope on the VEEV E2 envelope glycoprotein. In this study, we investigated the ability of F5 nIgG given prophylactically or therapeutically to protect mice from subcutaneous or aerosolized VEEV infection. F5 nIgG had potent ability to protect mice from infection by either route when administered 24h before exposure; however, mice treated 24h after aerosol exposure developed central nervous system infections but exhibited no clinical signs of disease. Infectious virus, viral antigen and RNA were detected in brains of both treated and untreated mice 2-6 days after aerosol exposure but were cleared from the brains of treated animals by 14-28 days after infection. This fully human MAb could be useful for prophylaxis or immediate therapy for individuals exposed to VEEV accidentally in the laboratory or during a deliberate release.

Safety and protective efficacy of INA-inactivated Venezuelan equine encephalitis virus: implication in vaccine development

We have previously shown that a hydrophobic alkylating compound, 1,5-iodonaphthyl-azide (INA) can efficiently inactivate the virulent strain of Venezuelan equine encephalitis virus (VEEV), V3000 in vitro. In this study, we have evaluated the safety of INA-inactivated V3000 and V3526 and the protective efficacy of INA-inactivated V3000. INA-inactivated V3000 and V3526 did not cause disease in suckling mice. RNA isolated from the INA-inactivated V3000 and V3526 was also not infectious. Immunization of adult mice with INA-inactivated V3000 induced an anti-VEEV antibody response and protected mice from virulent VEEV challenge. The protective efficacy of INA-inactivated V3000 increased with the use of adjuvants. Results suggest that inactivation of enveloped viruses by INA may occur by two independent mechanisms and the INA-inactivated VEEV elicit a protective antibody response in mice.

Antibody to the E3 glycoprotein protects mice against lethal venezuelan equine encephalitis virus infection

Six monoclonal antibodies were isolated that exhibited specificity for a furin cleavage site deletion mutant (V3526) of Venezuelan equine encephalitis virus (VEEV). These antibodies comprise a single competition group and bound the E3 glycoprotein of VEEV subtype I viruses but failed to bind the E3 glycoprotein of other alphaviruses. These antibodies neutralized V3526 virus infectivity but did not neutralize the parental strain of Trinidad donkey (TrD) VEEV. However, the E3-specific antibodies did inhibit the production of virus from VEEV TrD-infected cells. In addition, passive immunization of mice demonstrated that antibody to the E3 glycoprotein provided protection against lethal VEEV TrD challenge. This is the first recognition of a protective epitope in the E3 glycoprotein. Furthermore, these results indicate that E3 plays a critical role late in the morphogenesis of progeny virus after E3 appears on the surfaces of infected cells.

REVIEW PAPER

The encephalitides caused by Venezuelan (VEEV), eastern (EEEV), and western (WEEV) equine encephalitis viruses are important natural diseases of horses and humans and potential agents of biowarfare or bioterrorism. No licensed vaccines or specific therapies exist to prevent or treat human infections with VEEV, EEEV, or WEEV. Well-characterized animal models are needed to support the development of such medical countermeasures under the United States Food and Drug Administration’s “Animal Rule.” This review focuses on the pathological features and pathogenetic mechanisms of these alphaviral encephalitides in animal models, with an emphasis on aerosol infections. Infection of mice, nonhuman primates, and other species with VEEV, EEEV, and WEEV causes encephalitis and often death. There is great variability in the specific manifestations of disease in the different models, however. Many aspects of the disease in animal models and in humans remain to be characterized using modern methods. Especially needed is a better understanding of the fundamental mechanisms involved in 3 key phases of the pathogenesis of alphavirus encephalitis. These are the early extraneural phase, the process of neuroinvasion itself, and virus and host factors related to neurovirulence. A greater understanding of these aspects could provide avenues for the development of medical countermeasures and better establish suitable animal models of alphavirus encephalitis for testing them under the Animal Rule.

Evaluation of formalin inactivated V3526 virus with adjuvant as a next generation vaccine candidate for Venezuelan equine encephalitis virus

V3526, a genetically modified strain of Venezuelan equine encephalitis virus (VEEV), was formalin inactivated for evaluation as a next generation vaccine candidate for VEEV. In this study, we tested formalin-inactivated V3526 (fV3526) with and without adjuvant for immunogenicity and efficacy in BALB/c mice and results were compared to the existing inactivated VEEV vaccine, C84. Mice were vaccinated intramuscularly (IM) or subcutaneously (SC) with fV3526 formulations and challenged with VEEV IAB Trinidad donkey (VEEV TrD) strain by SC or aerosol exposure. Efficacy following SC or aerosol challenge was not significantly different between the fV3526 formulations or compared to C84 despite C84 being administered in more doses and higher concentration of viral protein per dose. These data support further evaluation of fV3526 formulations as a next generation VEEV vaccine.

Vaccines for Venezuelan equine encephalitis

Arboviruses are capable of causing encephalitis in animals and human population when transmitted by the vector or potentially via infectious aerosol. Recent re-emergence of Venezuelan equine encephalitis virus (VEEV) in South America emphasizes the importance of this pathogen to public health and veterinary medicine. Despite its importance no antivirals or vaccines against VEEV are currently available in the USA. Here we review some of the older and newer approaches aimed at generating a safe and immunogenic vaccine as well as most recent data about the mechanistic of protection in animal models of infection.

Comparison of the immunological responses and efficacy of gamma-irradiated V3526 vaccine formulations against subcutaneous and aerosol challenge with Venezuelan equine encephalitis virus subtype IAB

We recently developed a gamma-irradiation method to inactivate V3526, a live-attenuated Venezuelan equine encephalitis virus (VEEV) vaccine candidate. Dosage and schedule studies were conducted to evaluate the immunogenicity and efficacy of gamma-irradiated V3526 (gV3526). Subcutaneous (SC) and low dosage intramuscular (IM) administration of gV3526 were highly effective in protecting mice against a SC challenge with VEEV IA/B Trinidad Donkey strain, but not against an equivalent aerosol challenge. More robust immune responses and increased protective efficacy were noted when the IM dosage of gV3526 was increased. IM administration of gV3526 formulated with either CpG or CpG plus Alhydrogel further augmented the immune response in mice and resulted in 100% protection against aerosol challenge.

A multisystem approach for development and evaluation of inactivated vaccines for Venezuelan equine encephalitis virus (VEEV)

A multisystem approach was used to assess the efficiency of several methods for inactivation of Venezuelan equine encephalitis virus (VEEV) vaccine candidates. A combination of diverse assays (plaque, in vitro cytopathology and mouse neurovirulence) was used to verify virus inactivation, along with the use of a specific ELISA to measure retention of VEEV envelope glycoprotein epitopes in the development of several inactivated VEEV candidate vaccines derived from an attenuated strain of VEEV (V3526). Incubation of V3526 aliquots at temperatures in excess of 64 degrees C for periods >30 min inactivated the virus, but substantially reduced VEEV specific monoclonal antibody binding of the inactivated material. In contrast, V3526 treated either with formalin at concentrations of 0.1% or 0.5% (v/v) for 4 or 24 h, or irradiated with 50 kGy gamma radiation rendered the virus non-infectious while retaining significant levels of monoclonal antibody binding. Loss of infectivity of both the formalin inactivated (fV3526) and gamma irradiated (gV3526) preparations was confirmed via five successive blind passages on BHK-21 cells. Similarly, loss of neurovirulence for fV3526 and gV3526 was demonstrated via intracerebral inoculation of suckling BALB/c mice. Excellent protection against subcutaneous challenge with VEEV IA/B Trinidad donkey strain was demonstrated using a two dose immunization regimen with either fV3526 or gV3526. The combination of in vitro and in vivo assays provides a practical approach to optimize manufacturing process parameters for development of other inactivated viral vaccines.

Telemetric analysis to detect febrile responses in mice following vaccination with a live-attenuated virus vaccine

Non-human primates (NHP) are considered to be the most appropriate model for predicting how humans will respond to many infectious diseases. Due to ethical and monetary concerns associated with the use of NHP, rodent models that are as predictive of responses likely to be seen in human vaccine recipients are warranted. Using implanted telemetry devices, body temperature and activity were monitored in inbred and outbred mouse strains following administration of the live-attenuated vaccine for Venezuelan equine encephalitis virus (VEEV), V3526. Following analysis of individual mouse data, only outbred mouse strains showed changes in diurnal temperature and activity profiles following vaccination. Similar changes were observed following VEEV challenge of vaccinated outbred mice. From these studies, we conclude, outbred mouse strains implanted with telemeters are a sensitive model for predicting responses in humans following vaccination.

Understanding the alphaviruses: recent research on important emerging pathogens and progress towards their control

The alphaviruses were amongst the first arboviruses to be isolated, characterized and assigned a taxonomic status. They are globally very widespread, infecting a large variety of terrestrial animals, insects and even fish, and circulate both in the sylvatic and urban/peri-urban environment, causing considerable human morbidity and mortality. Nevertheless, despite their obvious importance as pathogens, there are currently no effective antiviral drugs with which to treat humans or animals infected by any of these viruses. The EU-supported project-VIZIER (Comparative Structural Genomics of Viral Enzymes Involved in Replication, FP6 PROJECT: 2004-511960) was instigated with an ultimate view of contributing to the development of antiviral therapies for RNA viruses, including the alphaviruses [Coutard, B., Gorbalenya, A.E., Snijder, E.J., Leontovich, A.M., Poupon, A., De Lamballerie, X., Charrel, R., Gould, E.A., Gunther, S., Norder, H., Klempa, B., Bourhy, H., Rohayemj, J., L'hermite, E., Nordlund, P., Stuart, D.I., Owens, R.J., Grimes, J.M., Tuckerm, P.A., Bolognesi, M., Mattevi, A., Coll, M., Jones, T.A., Aqvist, J., Unger, T., Hilgenfeld, R., Bricogne, G., Neyts, J., La Colla, P., Puerstinger, G., Gonzalez, J.P., Leroy, E., Cambillau, C., Romette, J.L., Canard, B., 2008. The VIZIER project: preparedness against pathogenic RNA viruses. Antiviral Res. 78, 37-46]. This review highlights some of the major features of alphaviruses that have been investigated during recent years. After describing their classification, epidemiology and evolutionary history and the expanding geographic distribution of Chikungunya virus, we review progress in understanding the structure and function of alphavirus replicative enzymes achieved under the VIZIER programme and the development of new disease control strategies.

CpG used as an adjuvant for an adenovirus-based Venezuelan equine encephalitis virus vaccine increases the immune response to the vector, but not to the transgene product

An adenovirus-based (ad-based) vaccine delivering antigens from the Alphavirus Venezuelan equine encephalitis virus (VEEV) is a strategy that offers clinical potential. A vaccine against VEEV is desirable because of the re-emerging nature of this virus, and also the potential that it may be used as a biological weapon. This study was designed to investigate whether the co-administration of CpG oligodeoxynucleotides (ODNs) with an ad-based VEEV vaccine could enhance the protective efficacy of the vaccine. We report that the co-administration of CpG ODN was unable to increase VEEV-specific antibody responses in mice, and was unable to increase the protective efficacy of the vaccine against aerosol challenge with virulent VEEV. However, it was noted that antibody responses directed against the adenovirus vaccine vector were increased, which may be detrimental, particularly in the context of homologous boosting.

IRES-dependent replication of Venezuelan equine encephalitis virus makes it highly attenuated and incapable of replicating in mosquito cells

The development of infectious cDNA for different alphaviruses opened an opportunity to explore their attenuation by extensively modifying the viral genomes, an approach that might minimize or exclude the reversion to the wild-type, pathogenic phenotype. Moreover, the genomes of such alphaviruses can be engineered to contain RNA elements that would be functional only in cells of vertebrate, but not insect, origin. In the present study, we developed a recombinant VEEV that is more attenuated than TC-83 and capable of replicating only in vertebrate cells. This phenotype was achieved by rendering the translation of the viral structural proteins, and ultimately viral replication, dependent on the internal ribosome entry site of encephalomyocarditis virus (EMCV IRES). This recombinant virus was viable, but required additional, adaptive mutations in nsP2 that strongly increased its replication rates. In spite of efficient replication in cultured vertebrate cells, the genetically modified VEEV demonstrated a highly attenuated phenotype in newborn mice, and yet induced protective immunity against VEEV infection.

Neurovirulence evaluation of Venezuelan equine encephalitis (VEE) vaccine candidate V3526 in nonhuman primates

Assessment of neurovirulence is a standard test for vaccines derived from virulent neurotropic viruses. This study evaluated the potential neurovirulence of V3526, a live attenuated vaccine derived from a full-length infectious clone of Venezuelan equine encephalitis virus (VEEV) Trinidad donkey strain (TrD), a comparator VEEV vaccine (TC-83), TrD, and process control material (PCM) in juvenile rhesus macaques. Following intrathalamic/intraspinal (i.t./i.s. ) or subcutaneous (s.c.) inoculations, animals were observed for periods of 18, 91 or 181 days for paresis, paralysis, neurological disorders and other signs of clinical illness. Blood was collected for measurement of viremia, VEEV neutralizing antibodies, hematologic parameters, and liver enzymes. Gross necropsies and histopathological examinations were conducted with emphasis on detecting lesions in the brain and spinal cord. Elevated temperatures (1-2 degrees C) were noted in several of the TrD and vaccine inoculated animals on Day 6 following inoculation and mean temperatures for the V3526 i.t./i.s. and TC-83 groups were higher than PCM group throughout the study Day 18. No significant differences were seen for weight or clinical chemistry results between vaccine and PCM inoculated groups. Clinically significant signs (Grades 3 or 4) were noted in three of 21 V3526 i.t./i.s. and three of 12 TC-83 inoculated animals, however, these signs resolved within 3 weeks for all V3526 i.t./i.s. and for two of three TC-83 inoculated animals. At Day 18 extensive lesions indicative of a viral infection were seen in brain sections of all four TrD inoculated animals and one of seven V3526 i.t./i.s. inoculated animals. Only scattered lesions, characterized by foci of gliosis and vessels with perivascular inflammation, were found in the sections from four TC-83 and six V3526 i.t./i.s. inoculated animals. The minimal histological changes observed at Day 18 resolved to baseline levels by Day 181 comparable to the PCM group. V3526 was immunogenic and essentially nonneurovirulent when administered via the clinically relevant subcutaneous route.

Complete inactivation of Venezuelan equine encephalitis virus by 1,5-iodonaphthylazide

Hydrophobic alkylating compounds like 1,5-iodonaphthylazide (INA) partitions into biological membranes and accumulates selectively into the hydrophobic domain of the lipid bilayer. Upon irradiation with far UV light, INA binds selectively to transmembrane proteins in the viral envelope and renders them inactive. Such inactivation does not alter the ectodomains of the membrane proteins thus preserving the structural and conformational integrity of immunogens on the surface of the virus. In this study, we have used INA to inactivate Venezuelan equine encephalitis virus (VEEV). Treatment of VEEV with INA followed by irradiation with UV light resulted in complete inactivation of the virus. Immuno-fluorescence for VEEV and virus titration showed no virus replication in-vitro. Complete loss of infectivity was also achieved in mice infected with INA treated plus irradiated preparations of VEEV. No change in the structural integrity of VEEV particles were observed after treatment with INA plus irradiation as assessed by electron microscopy. This data suggest that such inactivation strategies can be used for developing vaccine candidates for VEEV and other enveloped viruses.

Venezuelan equine encephalitis virus vaccine candidate (V3526) safety, immunogenicity and efficacy in horses

A new vaccine, V3526, is a live-attenuated virus derived by site-directed mutagenesis from a virulent clone of the Venezuelan equine encephalitis virus (VEEV) IA/B Trinidad donkey (TrD) strain, intended for human use in protection against Venezuelan equine encephalitis (VEE). Two studies were conducted in horses to evaluate the safety, immunogenicity, ability to boost and protective efficacy of V3526 against challenges of TrD and VEEV IE 64A99. Horses were vaccinated subcutaneously (SC) with 10(7), 10(5), 10(3) or 10(2) plaque-forming units (pfu) of V3526. Control horses were sham immunized. In the first study, challenge viruses (TrD or 64A99) were administered SC 28 days post-vaccination (PV). No viremia and only mild fluctuation in white blood cell counts were observed PV. None of the V3526 vaccinated horses showed clinical signs of disease or pathology of VEE post-challenge (PC). In contrast, control horses challenged SC with 10(4)pfu TrD became viremic and showed classical signs of VEE beginning on Day 3 PC, including elevated body temperature, anorexia, leukopenia and malaise. Moderate to severe encephalitis was found in three of five control horses challenged with TrD. Control horses challenged with 64A99 failed to develop detectable viremia, but did exhibit a brief febrile episode at 1-3 days PC. None of the 10 immunized horses challenged with 64A99 became pyrexic. Twenty four of 25 horses immunized with V3526 in the first study developed serum neutralizing antibody to TrD and 64A99 within 14 days PV. Vaccinations with V3526, at doses as low as 10(2)pfu, were safe and efficacious in protecting horses against a virulent TrD virus challenge. The second study supported that repeat dosing resulted in an increase in serum neutralizing antibody to TrD.

Replication and clearance of Venezuelan equine encephalitis virus from the brains of animals vaccinated with chimeric SIN/VEE viruses

Venezuelan equine encephalitis virus (VEEV) is an important, naturally emerging zoonotic pathogen. Recent outbreaks in Venezuela and Colombia in 1995, involving an estimated 100,000 human cases, indicate that VEEV still poses a serious public health threat. To develop a safe, efficient vaccine that protects against disease resulting from VEEV infection, we generated chimeric Sindbis (SIN) viruses expressing structural proteins of different strains of VEEV and analyzed their replication in vitro and in vivo, as well as the characteristics of the induced immune responses. None of the chimeric SIN/VEE viruses caused any detectable disease in adult mice after either intracerebral (i.c.) or subcutaneous (s.c.) inoculation, and all chimeras were more attenuated than the vaccine strain, VEEV TC83, in 6-day-old mice after i.c. infection. All vaccinated mice were protected against lethal encephalitis following i.c., s.c., or intranasal (i.n.) challenge with the virulent VEEV ZPC738 strain (ZPC738). In spite of the absence of clinical encephalitis in vaccinated mice challenged with ZPC738 via i.n. or i.c. route, we regularly detected high levels of infectious challenge virus in the central nervous system (CNS). However, infectious virus was undetectable in the brains of all immunized animals at 28 days after challenge. Hamsters vaccinated with chimeric SIN/VEE viruses were also protected against s.c. challenge with ZPC738. Taken together, our findings suggest that these chimeric SIN/VEE viruses are safe and efficacious in adult mice and hamsters and are potentially useful as VEEV vaccines. In addition, immunized animals provide a useful model for studying the mechanisms of the anti-VEEV neuroinflammatory response, leading to the reduction of viral titers in the CNS and survival of animals.

Genetically engineered, live, attenuated vaccines protect nonhuman primates against aerosol challenge with a virulent IE strain of Venezuelan equine encephalitis virus

Two live, attenuated strains of Venezuelan equine encephalitis virus (VEE), IE1150K and V3526, were administered to macaques to determine if they could elicit protection against an aerosol challenge with virulent VEE virus of the IE variety (VEEV-IE). These viruses were rescued from full-length cDNA clones of 68U201 (VEEV-IE variety) and Trinidad donkey (VEEV-IA/B variety), respectively, and both have a furin cleavage site deletion mutation and a second-site resuscitating mutation. Both vaccines elicited neutralizing antibodies to viruses of the homologous variety but not to viruses of the heterologous variety. Eight weeks after vaccination, the macaques were challenged by aerosol exposure to virulent 68U201. Macaques vaccinated with V3526 were protected as well as macaques inoculated with IE1009, the wild-type infectious clone of 68U201. However, IE1150K failed to significantly protect macaques relative to controls. V3526 has now been shown to protect macaques against both IA/B [Pratt WD, Davis NL, Johnston RE, Smith JF. Genetically engineered, live attenuated vaccines for Venezuelan equine encephalitis: testing in animal models. Vaccine 2003;21(25-26):3854-62] and IE strains of VEE viruses.

The immune response to equine arteritis virus: potential lessons for other arteriviruses

The members of the family Arteriviridae, genus Arterivirus, include equine arteritis virus (EAV), porcine reproductive and respiratory syndrome virus (PRRSV), lactate dehydrogenase-elevating virus (LDV) of mice, and simian hemorrhagic fever virus (SHFV). PRRSV is the newest member of the family (first isolated in North America and Europe in the early 1990s), whereas the other three viruses were recognized earlier (EAV in 1953, LDV in 1960, and SHFV in 1964). Although arterivirus infections are strictly species-specific, the causative agents share many biological and molecular properties, including their virion morphology, replication strategy, unique properties of their structural proteins, and their ability to establish distinctive persistent infections in their natural hosts. The arteriviruses are each antigenically distinct and cause different disease syndromes in their natural hosts. Similarly, the mechanism(s) responsible for the prolonged and/or persistent infections that characterize infections with each arterivirus in their natural hosts are remarkably different. The objective of this review is to compare and contrast the immune response to EAV with that to the other three arteriviruses, and emphasize the potential relevance of apparent similarities and differences in the neutralization characteristics of each virus.

Environmental hazard assessment of Venezuelan equine encephalitis virus vaccine candidate strain V3526

A hazard assessment of Venezuelan equine encephalitis (VEE) virus sub-types and vaccine candidates was performed according to standard risk assessment procedures. Data from published literature demonstrates a considerable degree of safety of V3526 when compared to TC-83 vaccine, the protective measure that has been used to protect laboratory workers for over four decades. V3526 is a new recombinant vaccine candidate that is a vastly different product with a diminished hazard to public health and the general environment. A weight-of-evidence (WOE)-based scheme was employed to assign weights for relevance, quality, and adequacy of evidence in published literature on medical pathology, epidemiology, pre-clinical investigational studies, and environmental studies. The results of this assessment indicated that V3526 has a low adverse impact on public health and the general environment. Although there are currently no human infectivity or pathogenicity data for V3526, existing evidence from published experimental animal studies reveals a diminished hazard for environmental transmission and distribution. Recently, the US Centers for Disease Control and Prevention (CDC) excluded V3526 from select agent requirements set forth under the Health and Human Services (HHS) regulations in Title 42 C.F.R. Part 73 and the US Department Agriculture (USDA) regulations set forth in Title 7 C.F.R. Part 331 and Title 9 C.F.R. Part 121. This paper summarizes the background, rationale, and hazard analysis used for assessing the environmental hazard of the VEE vaccine candidate strain V3526.

Vaccines for the prevention of diseases caused by potential bioweapons

The development of vaccines and implementation of vaccination programs are among the most important medical contributions to humanity. To date, vaccination has reduced morbidity and mortality from infectious diseases more than any other specific medical intervention. The intentional use of bioweapons against civilians (bioterrorism), recently highlighted by events around the world, has fueled interest in the development of vaccines for potential microbial agents of bioterror. This review discusses the microbial agents that are considered to pose the greatest risk to the public, the diseases associated with them, and the vaccines that are available for their prevention. The paucity of such vaccines and uncertainty regarding mechanisms of vaccine efficacy and the microbial antigens that elicit protection underscore the need for continued study of host-microbe interaction and the immune response to potential agents of bioterror for the development of new vaccines and immune-based therapies to combat their potential to harm the public.

Implementation of Biosurety Systems in a Department of Defense Medical Research Laboratory

New biosurety regulations and guidelines were implemented in 2003 because of increased concern for the safety and security of biological select agents and toxins (BSAT) that may be used as weapons of mass destruction. Biosurety is defined as the combination of security, biosafety, agent accountability, and personnel reliability needed to prevent unauthorized access to select agents of bioterrorism. These new regulations will lead to increased scrutiny of the use of select biological agents in registered research laboratories, but the regulations may have unintended effects on cost, progress, and perceptions in programs previously considered part of the academic research community. We review the history of biosurety, evolving guidelines, implementation of the regulations, and impacts at the lead research laboratory for medical biological defense for the Department of Defense.

Vaccines and animal models for arboviral encephalitides

Arthropod-borne viruses ("arboviruses") cause significant human illness ranging from mild, asymptomatic infection to fatal encephalitis or hemorrhagic fever. The most significant arboviruses causing human illness belong to genera in three viral families, Togaviridae, Flaviviridae, and Bunyaviridae. These viruses represent a significant public health threat to many parts of the world, and, as evidenced by the recent introduction of the West Nile virus (WNV) to the Western Hemisphere, they can no longer be considered specific to any one country or region of the world. Like most viral diseases, there are no specific therapies for the arboviral encephalitides; therefore, effective vaccines remain the front line of defense for these diseases. With this in mind, the development of new, more effective vaccines and the appropriate animal models in which to test them become paramount. In fact, for many important arboviruses (e.g. California serogroup and St. Louis encephalitis viruses), there are currently no approved vaccines available for human use. For others, such as the alphaviruses, human vaccines are available only as Investigational New Drugs, and thus are not in widespread use. On the other hand, safe and effective vaccines against tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JEV) have been in use for decades. New challenges in vaccine development have been met with new technologies in vaccine research. Many of the newer vaccines are now being developed by recombinant DNA technology. For example, chimeric virus vaccines have been developed using infectious clone technology for many of the arboviruses including, WNV, JEV, and TBEV. Other successful approaches have involved the use of naked DNA encoding and subsequently expressing the desired protective epitopes. Naked DNA vaccines have been used for TBEV and JEV and are currently under development for use against WNV. The development of less expensive, more authentic animal models to evaluate new vaccines against arboviral diseases will become increasingly important as these new approaches in vaccine research are realized. This article reviews the current status of vaccines, both approved for use and those in developmental stages, against the major arboviral encephalitides causing human disease. In addition, research on animal models, both past and present, for these diseases are discussed.

Genetically engineered, live attenuated vaccines for Venezuelan equine encephalitis: testing in animal models

The central objective of this research was to test molecularly defined, live attenuated Venezuelan equine encephalitis virus (VEEV) vaccine candidates that were produced through precise genetic manipulation of rationally selected viral nucleotide sequences. Molecular clones of vaccine candidates were constructed by inserting either three independently attenuating mutations or a PE2 cleavage-signal mutation with a second-site resuscitating mutation into full-length cDNA clones. Vaccine candidate viruses were recovered through DNA transcription and RNA transfection of cultured cells, and assessed in rodent and non-human primate models. Based on results from this assessment, one of the PE2 cleavage-signal mutants, V3526, was determined to be the best vaccine candidate for further evaluation for human use.

Recombinant sindbis/Venezuelan equine encephalitis virus is highly attenuated and immunogenic

Venezuelan equine encephalitis virus (VEEV) is an important, naturally emerging zoonotic virus. VEEV was a significant human and equine pathogen for much of the past century, and recent outbreaks in Venezuela and Colombia (1995), with about 100,000 human cases, indicate that this virus still poses a serious public health threat. The live attenuated TC-83 vaccine strain of VEEV was developed in the 1960s using a traditional approach of serial passaging in tissue culture of the virulent Trinidad donkey (TrD) strain. This vaccine presents several problems, including adverse, sometimes severe reactions in many human vaccinees. The TC-83 strain also retains residual murine virulence and is lethal for suckling mice after intracerebral (i.c.) or subcutaneous (s.c.) inoculation. To overcome these negative effects, we developed a recombinant, chimeric Sindbis/VEE virus (SIN-83) that is more highly attenuated. The genome of this virus encoded the replicative enzymes and the cis-acting RNA elements derived from Sindbis virus (SINV), one of the least human-pathogenic alphaviruses. The structural proteins were derived from VEEV TC-83. The SIN-83 virus, which contained an additional adaptive mutation in the nsP2 gene, replicated efficiently in common cell lines and did not cause detectable disease in adult or suckling mice after either i.c. or s.c. inoculation. However, SIN-83-vaccinated mice were efficiently protected against challenge with pathogenic strains of VEEV. Our findings suggest that the use of the SINV genome as a vector for expression of structural proteins derived from more pathogenic, encephalitic alphaviruses is a promising strategy for alphavirus vaccine development.

Alphavirus vectors for vaccine production and gene therapy

Alphavirus vectors demonstrate high expression of heterologous proteins in a broad range of host cells. Replication-deficient as well as replication-competent variants exist. Systemic delivery of many viral antigens has elicited strong antibody responses in immunized mice and primates, and protection against challenges with lethal viruses was obtained. Similarly, prophylactic vaccination was established against tumor challenges. Attention has been paid to the engineering of improved targeting to immunologically active cells, such as dendritic cells. In the area of gene therapy, intratumoral injections of alphavirus vectors have resulted in potentially promising tumor rejection. Moreover, encapsulation of alphavirus particles into liposomes demonstrated efficient tumor targeting in mice with severe combined immunodeficiency, which permitted the initiation of clinical trials for patients with advanced kidney carcinoma and melanoma.

Vaccine research efforts for filoviruses

Ebola and Marburg viruses belong to the family Filoviridae, and cause acute, frequently fatal, haemorrhagic fever in humans and non-human primates. No vaccines are available for human use. This review describes the status of research efforts to develop vaccines for these viruses and to identify the immune mechanisms of protection. The vaccine approaches discussed include DNA-based vaccines, and subunit vaccines vectored by adenovirus, alphavirus replicons, and vaccinia virus.

Chemical and biological weapons. Implications for anaesthesia and intensive care

In the wake of recent atrocities there has been renewed apprehension regarding the possibility of chemical and biological weapon (CBW) deployment by terrorists. Despite various international agreements that proscribe their use, certain states continue to develop chemical and biological weapons of mass destruction. Of greater concern, recent historical examples support the prospect that state-independent organizations have the capability to produce such weapons. Indeed, the deliberate deployment of anthrax has claimed several lives in the USA since September 11, 2001. In the event of a significant CBW attack, medical services would be stretched. However, victim survival may be improved by the prompt, coordinated response of military and civil authorities, in conjunction with appropriate medical care. In comparison with most other specialties, anaesthetists have the professional academic background in physiology and pharmacology to be able to understand the nature of the injuries caused by CBWs. Anaesthetists, therefore, play a vital role both in the initial resuscitation of casualties and in their continued treatment in an intensive care setting. This article assesses the current risk of CBW deployment by terrorists, considers factors which would affect the severity of an attack, and discusses the pathophysiology of those CBWs most likely to be used. The specific roles of the anaesthetist and intensivist in treatment are highlighted.

Role for mucosal immune responses and cell-mediated immune functions in protection from airborne challenge with Venezuelan equine encephalitis virus

Venezuelan equine encephalitis virus (VEEV) replicates in lymphoid tissues following peripheral inoculation and a high titre viraemia develops. Encephalitis develops after the virus enters the central nervous system from the blood, with the earliest neuronal involvement being via the olfactory nerve. Following aerosol challenge with virulent VEEV, the virus is thought to replicate in the nasal mucosa and there could be direct entry into the olfactory nerve via infected neuroepithelial cells. Protection from VEEV infection is believed to be primarily mediated by virus specific antibody. The correlation between protection and neutralising serum antibody titres is, however, inconsistent when the virulent virus is administered by the airborne route. This study demonstrates a link between antibody in serum and the nasal mucosa and protection by means of passive immunisation studies. Intra-nasal administration of antibody increased protection against airborne virus in Balb/c mice. Vaccination of mu MT strain mice that do not have functional B cells and cannot produce antibody revealed normal proliferation of spleen cells in vitro and robust cytokine production. Aerosol challenge of mu MT mice demonstrated that complete protection was only achieved when passive immunisation with antibody was supplemented with active immunisation with the TC-83 vaccine strain of the virus. This implies that cell-mediated immune functions are required for protection against airborne challenge with virulent VEEV.

Alphavirus replicon particles expressing the two major envelope proteins of equine arteritis virus induce high level protection against challenge with virulent virus in vaccinated horses

Replicon particles derived from a vaccine strain of Venezuelan equine encephalitis (VEE) virus were used as vectors for expression in vivo of the major envelope proteins (G(L) and M) of equine arteritis virus (EAV), both individually and in heterodimer form (G(L)/M). The immunogenicity of the different replicons was evaluated in horses, as was their ability to protectively immunize horses against intranasal and intrauterine challenge with a virulent strain of EAV (EAV KY84). Horses immunized with replicons that express both the G(L) and M proteins in heterodimer form developed neutralizing antibodies to EAV, shed little or no virus, and developed only mild or inapparent signs of equine viral arteritis (EVA) after challenge with EAV KY84. In contrast, unvaccinated horses and those immunized with replicons expressing individual EAV envelope proteins (M or G(L)) shed virus for 6-10 days in their nasal secretions and developed severe signs of EVA after challenge. These data confirm that replicons that co-express the G(L) and M envelope proteins effectively, induce EAV neutralizing antibodies and protective immunity in horses.

Systemic, mucosal, and heterotypic immune induction in mice inoculated with Venezuelan equine encephalitis replicons expressing Norwalk virus-like particles

Norwalk-like viruses (NLVs) are a diverse group of single-stranded, nonenveloped, positive-polarity RNA viruses and are the leading cause of epidemic acute gastroenteritis in the United States. In this study, the major capsid gene of Norwalk virus, the prototype NLV, has been cloned and expressed in mammalian cells using a Venezuelan equine encephalitis (VEE) replicon expression system. Upon infection of baby hamster kidney (BHK) cells with VEE replicon particles (VRPs), the Norwalk virus capsid proteins self-assemble to generate high titers of Norwalk virus-like particles (VLPs) that are morphologically and antigenically analogous to wild-type Norwalk virus. Mice inoculated subcutaneously with VRPs expressing the Norwalk virus capsid protein (VRP-NV1) developed systemic and mucosal immune responses to Norwalk VLPs, as well as heterotypic antibody responses to the major capsid protein from another genogroup I NLV strain (NCFL) isolated from a recent outbreak. A second Norwalk virus capsid clone (NV2) containing three amino acid codon mutations from the NV1 clone was also expressed using VEE replicons (VRP-NV2), but upon infection of BHK cells failed to confer VLP self-assembly. Mice inoculated with VRP-NV2 elicited reduced systemic and mucosal immune responses to Norwalk VLPs, demonstrating the importance and potential utility of endogenous VLP presentation for maximum immune induction. Inoculation with either VRP-NV1 or VRP-NV2 resulted in serum antibody responses far superior to the induction in mice dosed orally with VLPs that were prepared using the VEE-NV1 replicon construct, a regimen similar to current models for NLV vaccination. Expression of NLV VLPs in mammalian cells offers a powerful approach for the design of novel NLV vaccines, either alone or in combination with current vaccination models.

Onset and duration of protective immunity to IA/IB and IE strains of Venezuelan equine encephalitis virus in vaccinated mice

Three vaccines developed for protection against IA/IB subtypes of Venezuelan equine encephalitis (VEE) virus were evaluated in mice for the ability to protect against systemic and mucosal challenges with a virulent virus of the IE subtype. The vaccines were the formaldehyde-inactivated C-84 and live attenuated TC-83 vaccines currently administered to people under investigational new drug (IND) status, and a new live attenuated vaccine candidate, V3526. V3526 was superior for inducing protection to VEE IA/IB within a week of vaccination, and protection persisted for at least a year. All three vaccines induced long-term clinical protection against peripheral or mucosal challenge with IE virus, with the mucosal immunity induced by attenuated vaccines lasting longer than that induced by the inactivated vaccine. These data show that the molecularly cloned V3526 vaccine induces equivalent or improved immunity to homologous and heterologous VEE viruses than the existing vaccines.