Development and evaluation of a formalin-inactivated West Nile Virus vaccine (WN-VAX) for a human vaccine candidate

Recent Advancements in Mosquito-Borne Flavivirus Vaccine Development

Lately, the global incidence of flavivirus infection has been increasing dramatically and presents formidable challenges for public health systems around the world. Most clinically significant flaviviruses are mosquito-borne, such as the four serotypes of dengue virus, Zika virus, West Nile virus, Japanese encephalitis virus and yellow fever virus. Until now, no effective antiflaviviral drugs are available to fight flaviviral infection; thus, a highly immunogenic vaccine would be the most effective weapon to control the diseases. In recent years, flavivirus vaccine research has made major breakthroughs with several vaccine candidates showing encouraging results in preclinical and clinical trials. This review summarizes the current advancement, safety, efficacy, advantages and disadvantages of vaccines against mosquito-borne flaviviruses posing significant threats to human health.

The Long Road Toward COVID-19 Herd Immunity: Vaccine Platform Technologies and Mass Immunization Strategies

There is an urgent need for effective countermeasures against the current emergence and accelerating expansion of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Induction of herd immunity by mass vaccination has been a very successful strategy for preventing the spread of many infectious diseases, hence protecting the most vulnerable population groups unable to develop immunity, for example individuals with immunodeficiencies or a weakened immune system due to underlying medical or debilitating conditions. Therefore, vaccination represents one of the most promising counter-pandemic measures to COVID-19. However, to date, no licensed vaccine exists, neither for SARS-CoV-2 nor for the closely related SARS-CoV or Middle East respiratory syndrome-CoV. In addition, a few vaccine candidates have only recently entered human clinical trials, which hampers the progress in tackling COVID-19 infection. Here, we discuss potential prophylactic interventions for SARS-CoV-2 with a focus on the challenges existing for vaccine development, and we review pre-clinical progress and ongoing human clinical trials of COVID-19 vaccine candidates. Although COVID-19 vaccine development is currently accelerated via so-called fast-track programs, vaccines may not be timely available to have an impact on the first wave of the ongoing COVID-19 pandemic. Nevertheless, COVID-19 vaccines will be essential in the future for reducing morbidity and mortality and inducing herd immunity, if SARS-CoV-2 becomes established in the population like for example influenza virus.

Comparative Pathology of West Nile Virus in Humans and Non-Human Animals

West Nile virus (WNV) continues to be a major cause of human arboviral neuroinvasive disease. Susceptible non-human vertebrates are particularly diverse, ranging from commonly affected birds and horses to less commonly affected species such as alligators. This review summarizes the pathology caused by West Nile virus during natural infections of humans and non-human animals. While the most well-known findings in human infection involve the central nervous system, WNV can also cause significant lesions in the heart, kidneys and eyes. Time has also revealed chronic neurologic sequelae related to prior human WNV infection. Similarly, neurologic disease is a prominent manifestation of WNV infection in most non-human non-host animals. However, in some avian species, which serve as the vertebrate host for WNV maintenance in nature, severe systemic disease can occur, with neurologic, cardiac, intestinal and renal injury leading to death. The pathology seen in experimental animal models of West Nile virus infection and knowledge gains on viral pathogenesis derived from these animal models are also briefly discussed. A gap in the current literature exists regarding the relationship between the neurotropic nature of WNV in vertebrates, virus propagation and transmission in nature. This and other knowledge gaps, and future directions for research into WNV pathology, are addressed.

An observer blinded, randomized, placebo-controlled, phase I dose escalation trial to evaluate the safety and immunogenicity of an inactivated West Nile virus Vaccine, HydroVax-001, in healthy adults

Background

West Nile virus (WNV) is the most common mosquito-borne infection in the United States. HydroVax-001 WNV is a hydrogen peroxide inactivated, whole virion (WNV-Kunjin strain) vaccine adjuvanted with aluminum hydroxide.

Methods

We performed a phase 1, randomized, placebo-controlled, double-blind (within dosing group), dose escalation clinical trial of the HydroVax-001 WNV vaccine administered via intramuscular injection. This trial evaluated 1 mcg and 4 mcg dosages of HydroVax-001 WNV vaccine given intramuscularly on day 1 and day 29 in healthy adults. The two dosing groups of HydroVax-001 were enrolled sequentially and each group consisted of 20 individuals who received HydroVax-001 and 5 who received placebo. Safety was assessed at all study days (days 1, 2, 4 and 15 post dose 1, and days 1, 2, 4, 15, 29, 57, 180 and 365 post dose 2), and reactogenicity was assessed for 14 days after administration of each dose. Immunogenicity was measured by WNV-specific plaque reduction neutralization tests (PRNT₅₀) in the presence or absence of added complement or by WNV-specific enzyme-linked immunosorbent assays (ELISA).

Results

HydroVax-001 was safe and well-tolerated as there were no serious adverse events or concerning safety signals. At the 1 mcg dose, HydroVax-001 was not immunogenic by PRNT₅₀ but elicited up to 41% seroconversion by WNV-specific ELISA in the per-protocol population (PP) after the second dose. At the 4 mcg dose, HydroVax-001 elicited neutralizing antibody responses in 31% of the PP following the second dose. In the presence of added complement, PRNT₅₀ seroconversion rates increased to 50%, and 75% seroconversion was observed by WNV-specific ELISA.

Conclusions

The HydroVax-001 WNV vaccine was found to be modestly immunogenic and welltolerated at all dose levels.

Japanese encephalitis vaccine-facilitated dengue virus infection-enhancement antibody in adults

Background

Dengue virus (DENV) and Japanese encephalitis virus (JEV) belong to the genus Flavivirus, and infection with a virus within this genus induces antibodies that are cross-reactive to other flaviviruses. Particularly in DENV infection, antibodies to DENV possess two competing activities: neutralizing activity and infection-enhancing activity. These antibody activities are considered central in modulating clinical outcomes of DENV infection. Here, we determined the neutralizing and infection-enhancing activity of DENV cross-reactive antibodies in adults before and after JE vaccination.

Methods

Participants were 77 Japanese adults who had received a single dose of inactivated Vero cell-derived JE vaccine. A total of 154 serum samples were obtained either before or approximately a month after a single dose of JE vaccination. The antibody-dependent enhancement (ADE) activity to each of four DENV serotypes and the neutralizing activities to DENV and to JEV were determined in each of the serum samples by using baby hamster kidney (BHK) cells and FcγR-expressing BHK cells.

Results

A total of 18 post-JE immunization samples demonstrated cross-reactivity to DENV in an anti-DENV IgG ELISA. DENV neutralizing antibodies were not detected after JE vaccination in this study. However, undiluted post-JE vaccination serum samples from 26 participants demonstrated monotypic and heterotypic ADE activity to DENV. ADE activity was also observed in 1:10-diluted samples from 35 of the JE vaccine recipients (35/77, 45 %).

Conclusion

In summary, JE vaccination induced DENV cross-reactive antibodies, and at sub-neutralizing levels, these DENV cross-reactive antibodies possess DENV infection-enhancement activity. The results also indicate that cross-reactivity to DENV is associated with high levels of JEV neutralizing antibodies and, the DENV cross-reactivity is further facilitated by JE vaccination.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1873-8) contains supplementary material, which is available to authorized users.

Comparison of β-Propiolactone and Formalin Inactivation on Antigenicity and Immune Response of West Nile Virus

West Nile Virus (WNV) is a pathogenic arbovirus that belongs to genus Flavivirus under family Flaviviridae. Till now there are no approved vaccines against WNV for human use. In this study, the effect of two alkylating agents, formaldehyde and β-PL, generally used for inactivated vaccine preparation, was assessed on the basis of antigenic and immunogenic potential of the inactivated WNV. Lineage 5 WNV isolates were inactivated by both formalin and β-PL treatments. Inactivation was confirmed by repeated passage in BHK-21 cell line and infant mice. Viruses inactivated by both the treatments showed higher antigenicity. Immune response in mice model showed serum anti-WNV antibody titre was moderately higher in formalin inactivated antigen compared to β-PL inactivated antigen. However, no significant differences were observed in neutralization antibody titre. In conclusion, we can state that both formaldehyde and β-PL inactivation processes were found to be equally efficient for inactivation of WNV. However, they need to be compared with other inactivating agents along with study on cell mediated immune response.

The efficacy of inactivated West Nile vaccine (WN-VAX) in mice and monkeys

Background

West Nile virus (WNV) belonging to the genus Flavivirus of the family Flaviviridae causes nervous system disorder in humans, horses and birds. Licensed WNV vaccines are available for use in horses but not for humans. We previously developed an inactivated West Nile virus vaccine (WN-VAX) using a seed virus from West Nile virus (WNV NY99) that was originally isolated in New York City in 1999. In this study, we report the immunogenicity of WN-VAX in both mice and non-human primates.

Findings

The WN-VAX immunized mice showed protection against lethal infection with WNV NY99. The challenge test performed on mice passively immunized with serum from other mice that were previously immunized with WN-VAX confirmed that the neutralizing antibody titers of more than 1log10 protected the passively immunized mice from WNV lethal infection. Furthermore, monkeys (Macaca fascicularis) immunized three times with 2.5 μg, 5 μg or 10 μg/dose of WN-VAX exhibited neutralizing antibodies in their sera with titers of more than 2log10 after the second immunization.

Conclusions

The WN-VAX was protective in mice both by active and passive immunizations and was immunogenic in monkeys. These results suggest that the vaccine developed in this study may be a potential WNV vaccine candidate for human use.

Immunogenic potential and protective efficacy of formalin inactivated circulating Indian strain of West Nile virus

OBJECTIVE

To assess the best suitable condition for virus inactivation, and to study the immunogenic potential and protective efficacy of a circulating West Nile virus (WNV) strain in Assam.

METHODS

Bulk preparation of circulating WNV: WNIRGC07 (GeneBank ID: HQ246154), was undertaken in a bioreactor using cytodex-1. Virus Inactivation was done in three different conditions; 22 °C, 4 °C and room temperature. The virus preparations were evaluated for antigenicity by ELISA and toxicity by cell proliferation kit. Virus efficacy was done in-vivo on swiss albino mice against standard Indian WNV and Japanese encephalitis virus (JEV) strain. Humoral and cell mediated immune response was evaluated in mice sera by ELISA and neutralization assay.

RESULTS

Inactivation at 22 °C was found to be more suitable in terms of less toxicity and high antigenicity. The same was selected to study the immune response and efficacy in mice. It induced neutralizing antibody titre of 1: 625 and high IgG response. In vivo experiment showed 100% protective efficacy against WNV and 20.8% cross protective efficacy against JEV. Further assessment of cellular immunity through immunized mice revealed augmentation of high levels of pro-inflammatory cytokines and moderate levels of anti-cytokines indicating a mixed balance of Th1 and Th2 response.

CONCLUSIONS

Findings suggest that formalin inactivated Indian WNV strain has a good immunogenic potential. This is the first study on assessment of immunogenic potential of a lineage 5 strain of WNV. Our study reveals that it would be a promising and effective candidate for vaccine studies which warrants further evaluation.

Development of chimaeric West Nile virus attenuated vaccine candidate based on the Japanese encephalitis vaccine strain SA14-14-2

Mosquito-borne flaviviruses include a large group of important human medical pathogens. Several chimaeric flaviviruses have been constructed, and show potential for vaccine development. Although Japanese encephalitis virus (JEV) live vaccine SA14-14-2 has been widely used with ideal safety and efficacy profiles, no chimaeric flavivirus based on the JEV vaccine has been described to date. Based on the reverse genetic system of the JEV vaccine SA14-14-2, a novel live chimaeric flavivirus carrying the protective antigens of West Nile virus (WNV) was constructed and recovered in this study. The resulting chimaera (ChinWNV) replicated efficiently in both mammalian and mosquito cells and possessed genetic stability after in vitro serial passaging. ChinWNV exhibited a small-plaque phenotype, and its replication was significantly restricted in mouse peripheral blood and brain compared with parental WNV. Importantly, ChinWNV was highly attenuated with regard to both neurovirulence and neuroinvasiveness in mice. Furthermore, a single ChinWNV immunization stimulated robust WNV-specific adaptive immune responses in mice, conferring significant protection against lethal WNV infection. Our results demonstrate that chimaeric flaviviruses based on the JEV vaccine can serve as a powerful platform for vaccine development, and that ChinWNV represents a potential WNV vaccine candidate that merits further development.

TLR3- and MyD88-dependent signaling differentially influences the development of West Nile virus-specific B cell responses in mice following immunization with RepliVAX WN, a single-cycle flavivirus vaccine candidate

Recognition of conserved pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs) results in the activation of innate signaling pathways that drive the innate immune response and ultimately shape the adaptive immune response. RepliVAX WN, a single-cycle flavivirus (SCFV) vaccine candidate derived from West Nile virus (WNV), is intrinsically adjuvanted with multiple PAMPs and induces a vigorous anti-WNV humoral response. However, the innate mechanisms that link pattern recognition and development of vigorous antigen-specific B cell responses are not completely understood. Moreover, the roles of individual PRR signaling pathways in shaping the B cell response to this live attenuated SCFV vaccine have not been established. We examined and compared the role of TLR3- and MyD88-dependent signaling in the development of anti-WNV-specific antibody-secreting cell responses and memory B cell responses induced by RepliVAX WN. We found that MyD88 deficiency significantly diminished B cell responses by impairing B cell activation, development of germinal centers (GC), and the generation of long-lived plasma cells (LLPCs) and memory B cells (MBCs). In contrast, TLR3 deficiency had more effect on maintenance of GCs and development of LLPCs, whereas differentiation of MBCs was unaffected. Our data suggest that both TLR3- and MyD88-dependent signaling are involved in the intrinsic adjuvanting of RepliVAX WN and differentially contribute to the development of vigorous WNV-specific antibody and B cell memory responses following immunization with this novel SCFV vaccine.

An inactivated cell culture Japanese encephalitis vaccine (JE-ADVAX) formulated with delta inulin adjuvant provides robust heterologous protection against West Nile encephalitis via cross-protective memory B cells and neutralizing antibody

West Nile virus (WNV), currently the cause of a serious U.S. epidemic, is a mosquito-borne flavivirus and member of the Japanese encephalitis (JE) serocomplex. There is currently no approved human WNV vaccine, and treatment options remain limited, resulting in significant mortality and morbidity from human infection. Given the availability of approved human JE vaccines, this study asked whether the JE-ADVAX vaccine, which contains an inactivated cell culture JE virus antigen formulated with Advax delta inulin adjuvant, could provide heterologous protection against WNV infection in wild-type and β2-microglobulin-deficient (β2m(-/-)) murine models. Mice immunized twice or even once with JE-ADVAX were protected against lethal WNV challenge even when mice had low or absent serum cross-neutralizing WNV titers prior to challenge. Similarly, β2m(-/-) mice immunized with JE-ADVAX were protected against lethal WNV challenge in the absence of CD8(+) T cells and prechallenge WNV antibody titers. Protection against WNV could be adoptively transferred to naive mice by memory B cells from JE-ADVAX-immunized animals. Hence, in addition to increasing serum cross-neutralizing antibody titers, JE-ADVAX induced a memory B-cell population able to provide heterologous protection against WNV challenge. Heterologous protection was reduced when JE vaccine antigen was administered alone without Advax, confirming the importance of the adjuvant to induction of cross-protective immunity. In the absence of an approved human WNV vaccine, JE-ADVAX could provide an alternative approach for control of a major human WNV epidemic.

Phase II, dose ranging study of the safety and immunogenicity of single dose West Nile vaccine in healthy adults ≥ 50 years of age

INTRODUCTION

ChimeriVax-WN02 is a live, attenuated chimeric vaccine for protection against West Nile virus (WNV) produced by insertion of the genes encoding the pre-membrane (prM) and envelope (E) proteins of WNV (strain NY99) into the yellow fever 7D vaccine virus. This Phase II, randomized, double-blind, placebo-controlled, multi-center study in the US assessed the immunogenicity, viremia, and safety of the ChimeriVax-WN02 vaccine.

METHODS

The study included adults in general good health. Subjects aged ≥ 50 years were randomized to one of four treatment groups: ChimeriVax-WN02 4 × 10(3) plaque-forming units (pfu) (n=122), 4 × 10(4)pfu (n=124), 4 × 10(5)pfu (n=113), or placebo (n=120). A subset of subjects was randomized to assess viremia after vaccination at three different dose levels. Subjects were followed for safety up to 6 months after vaccination.

RESULTS

A total of 121 subjects for WN024 × 10(3), 122 for WN02 4 × 10(4), 110 for WN02 4 × 10(5), and 120 for the placebo group completed the study up to the 6-month safety follow-up. Seroconversion, as measured by plaque reduction neutralization test (PRNT), was achieved at Day 28 by 92.1%, 93.2%, and 95.4% of subjects in the WN02 4 × 10(3), the WN02 4 × 10(4), and the WN02 4 × 10(5) groups, respectively. Viremia was transient, detected between Days 2 and 14 but not at Day 28, and in most cases did not reach the quantification threshold. The percentage of subjects reporting at least one event of reactogenicity was similar in the placebo and active vaccine groups and showed no dose relationship.

CONCLUSIONS

The ChimeriVax-WN02 vaccine was highly immunogenic and well tolerated among subjects ≥ 50 years old at all dose levels.