Potent vesicular stomatitis virus-based avian influenza vaccines provide long-term sterilizing immunity against heterologous challenge

A single dose of a vesicular stomatitis virus-based influenza vaccine confers rapid protection against H5 viruses from different clades

The avian influenza virus outbreak in 1997 highlighted the potential of the highly pathogenic H5N1 virus to cause severe disease in humans. Therefore, effective vaccines against H5N1 viruses are needed to counter the potential threat of a global pandemic. We have previously developed a fast-acting and efficacious vaccine against Ebola virus (EBOV) using the vesicular stomatitis virus (VSV) platform. In this study, we generated recombinant VSV-based H5N1 influenza virus vectors to demonstrate the feasibility of this platform for a fast-acting pan-H5 influenza virus vaccine. We chose multiple approaches regarding antigen design and genome location to define a more optimized vaccine approach. After the VSV-based H5N1 influenza virus constructs were recovered and characterized in vitro, mice were vaccinated by a single dose or prime/boost regimen followed by challenge with a lethal dose of the homologous H5 clade 1 virus. We found that a single dose of VSV vectors expressing full-length hemagglutinin (HAfl) were sufficient to provide 100% protection. The vaccine vectors were fast-acting as demonstrated by uniform protection when administered 3 days prior to lethal challenge. Moreover, single vaccination induced cross-protective H5-specific antibodies and protected mice against lethal challenge with various H5 clade 2 viruses, highlighting the potential of the VSV-based HAfl as a pan-H5 influenza virus emergency vaccine.

Oncolytic Vesicular Stomatitis Virus as a Viro-Immunotherapy: Defeating Cancer with a "Hammer" and "Anvil"

Oncolytic viruses have gained much attention in recent years, due, not only to their ability to selectively replicate in and lyse tumor cells, but to their potential to stimulate antitumor immune responses directed against the tumor. Vesicular stomatitis virus (VSV), a negative-strand RNA virus, is under intense development as an oncolytic virus due to a variety of favorable properties, including its rapid replication kinetics, inherent tumor specificity, and its potential to elicit a broad range of immunomodulatory responses to break immune tolerance in the tumor microenvironment. Based on this powerful platform, a multitude of strategies have been applied to further improve the immune-stimulating potential of VSV and synergize these responses with the direct oncolytic effect. These strategies include: 1. modification of endogenous virus genes to stimulate interferon induction; 2. virus-mediated expression of cytokines or immune-stimulatory molecules to enhance anti-tumor immune responses; 3. vaccination approaches to stimulate adaptive immune responses against a tumor antigen; 4. combination with adoptive immune cell therapy for potentially synergistic therapeutic responses. A summary of these approaches will be presented in this review.

Viral vector-based influenza vaccines

Antigenic drift of seasonal influenza viruses and the occasional introduction of influenza viruses of novel subtypes into the human population complicate the timely production of effective vaccines that antigenically match the virus strains that cause epidemic or pandemic outbreaks. The development of game-changing vaccines that induce broadly protective immunity against a wide variety of influenza viruses is an unmet need, in which recombinant viral vectors may provide. Use of viral vectors allows the delivery of any influenza virus antigen, or derivative thereof, to the immune system, resulting in the optimal induction of virus-specific B- and T-cell responses against this antigen of choice. This systematic review discusses results obtained with vectored influenza virus vaccines and advantages and disadvantages of the currently available viral vectors.

Cross-protection of newly emerging HPAI H5 viruses by neutralizing human monoclonal antibodies: A viable alternative to oseltamivir

Newly emerging highly pathogenic avian influenza (HPAI) H5N2, H5N3, H5N5, H5N6, H5N8 and H5N9 viruses have been spreading in poultry and wild birds. The H5N6 viruses have also caused 10 human infections with 4 fatal cases in China. Here, we assessed the cross-neutralization and cross-protection of human and mouse monoclonal antibodies against 2 viruses: a HPAI H5N8 virus, A/chicken/Netherlands/14015526/2014 (NE14) and a HPAI H5N6 virus, A/Sichuan/26221/2014 (SC14). The former was isolated from an infected chicken in Netherlands in 2014 and the latter was isolated from an infected human patient in Sichuan, China. We show that antibodies FLA5.10, FLD21.140, 100F4 and 65C6, but not AVFluIgG01, AVFluIgG03, S139/1 and the VRC01 control, potently cross-neutralize the H5N8 NE14 and H5N6 SC14 viruses. Furthermore, we show that a single injection of >1 mg/kg of antibody 100F4 at 4 hours before, or 20 mg/kg antibody 100F4 at 72 hours after, a lethal dose of H5N8 NE14 enables mice to withstand the infection. Finally, we show that a single injection of 0.5 or 1 mg/kg antibody 100F4 prophylactically or 10 mg/kg 100F4 therapeutically outperforms a 5-day course of 10 mg/kg/day oseltamivir treatment against lethal H5N8 NE14 or H5N6 SC14 infection in mice. Our results suggest that further preclinical evaluation of human monoclonal antibodies against newly emerging H5 viruses is warranted.

Vaccination with Vesicular Stomatitis Virus-Vectored Chimeric Hemagglutinins Protects Mice against Divergent Influenza Virus Challenge Strains

Seasonal influenza virus infections continue to cause significant disease each year, and there is a constant threat of the emergence of reassortant influenza strains causing a new pandemic. Available influenza vaccines are variably effective each season, are of limited scope at protecting against viruses that have undergone significant antigenic drift, and offer low protection against newly emergent pandemic strains. "Universal" influenza vaccine strategies that focus on the development of humoral immunity directed against the stalk domains of the viral hemagglutinin (HA) show promise for protecting against diverse influenza viruses. Here, we describe such a strategy that utilizes vesicular stomatitis virus (VSV) as a vector for chimeric hemagglutinin (cHA) antigens. This vaccination strategy is effective at generating HA stalk-specific, broadly cross-reactive serum antibodies by both intramuscular and intranasal routes of vaccination. We show that prime-boost vaccination strategies provide protection against both lethal homologous and heterosubtypic influenza challenge and that protection is significantly improved with intranasal vaccine administration. Additionally, we show that vaccination with VSV-cHAs generates greater stalk-specific and cross-reactive serum antibodies than does vaccination with VSV-vectored full-length HAs, confirming that cHA-based vaccination strategies are superior at generating stalk-specific humoral immunity. VSV-vectored influenza vaccines that express chimeric hemagglutinin antigens offer a novel means for protecting against widely diverging influenza viruses.

IMPORTANCE

Universal influenza vaccination strategies should be capable of protecting against a wide array of influenza viruses, and we have developed such an approach utilizing a single viral vector system. The potent antibody responses that these vaccines generate are shown to protect mice against lethal influenza challenges with highly divergent viruses. Notably, intranasal vaccination offers significantly better protection than intramuscular vaccination in a lethal virus challenge model. The results described in this study offer insights into the mechanisms by which chimeric hemagglutinin (HA)-based vaccines confer immunity, namely, that the invariant stalk of cHA antigens is superior to full-length HA antigens at inducing cross-reactive humoral immune responses and that VSV-cHA vaccine-induced protection varies by site of inoculation, and contribute to the further development of universal influenza virus vaccines.

Characterization of a Bivalent Vaccine Capable of Inducing Protection Against Both Ebola and Cross-clade H5N1 Influenza in Mice

Background. Ebola virus (EBOV) is a lethal pathogen that causes up to 90% mortality in humans, whereas H5N1 avian influenza has a 60% fatality rate. Both viruses are considered pandemic threats. The objective was to evaluate the protective efficacy of a bivalent, recombinant vesicular stomatitis virus vaccine expressing both the A/Hanoi/30408/2005 H5N1 hemagglutinin and the EBOV glycoprotein (VSVΔG-HA-ZGP) in a lethal mouse model of infection.

Methods. Mice were vaccinated 28 days before or 30 minutes after a lethal challenge with mouse-adapted EBOV or selected H5N1 influenza viruses from clades 0, 1, and 2. Animals were monitored for weight loss and survival, in addition to humoral and cell-mediated responses after immunization.

Results. A single VSVΔG-HA-ZGP injection was efficacious when administered 28 days before a homologous H5N1 and/or mouse-adapted EBOV challenge, as well as a heterologous H5N1 challenge. Postexposure protection was only observed in vaccinated animals challenged with homologous H5N1 and/or mouse-adapted EBOV. Analysis of the adaptive immune response postvaccination revealed robust specific T- and B-cell responses, including a potent hemagglutinin inhibition antibody response against all H5N1 strains tested.

Conclusions. The results highlight the ability of vesicular stomatitis virus–vectored vaccines to rapidly confer protection against 2 unrelated pathogens and stimulate cross-protection against H5N1 influenza viruses.

A viable recombinant rhabdovirus lacking its glycoprotein gene and expressing influenza virus hemagglutinin and neuraminidase is a potent influenza vaccine

The emergence of novel influenza viruses that cause devastating human disease is an ongoing threat and serves as an impetus for the continued development of novel approaches to influenza vaccines. Influenza vaccine development has traditionally focused on producing humoral and/or cell-mediated immunity, often against the viral surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). Here, we describe a new vaccine candidate that utilizes a replication-defective vesicular stomatitis virus (VSV) vector backbone that lacks the native G surface glycoprotein gene (VSVΔG). The expression of the H5 HA of an H5N1 highly pathogenic avian influenza virus (HPAIV), A/Vietnam/1203/04 (VN1203), and the NA of the mouse-adapted H1N1 influenza virus A/Puerto Rico/8/34 (PR8) in the VSVΔG vector restored the ability of the recombinant virus to replicate in cell culture, without the requirement for the addition of trypsin. We show here that this recombinant virus vaccine candidate was nonpathogenic in mice when given by either the intramuscular or intranasal route of immunization and that the in vivo replication of VSVΔG-H5N1 is profoundly attenuated. This recombinant virus also provided protection against lethal H5N1 infection after a single dose. This novel approach to vaccination against HPAIVs may be widely applicable to other emerging strains of influenza virus.

IMPORTANCE

Preparation for a potentially catastrophic influenza pandemic requires novel influenza vaccines that are safe, can be produced and administered quickly, and are effective, both soon after administration and for a long duration. We have created a new influenza vaccine that utilizes an attenuated vesicular stomatitis virus (VSV) vector, to deliver and express influenza virus proteins against which vaccinated animals develop potent antibody responses. The influenza virus hemagglutinin and neuraminidase proteins, expressed on the surface of VSV particles, allowed this vaccine to grow in cell culture and induced a potent antibody response in mice that was effective against infection with a lethal influenza virus. The mice showed no adverse reactions to the vaccine, and they were protected against an otherwise lethal influenza infection after only 14 days postvaccination and after as many as 140 days postvaccination. The ability to rapidly produce this safe and effective vaccine in cell culture is additionally advantageous.

Immunization with vesicular stomatitis virus vaccine expressing the Ebola glycoprotein provides sustained long-term protection in rodents

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VSV-based vaccine protects guinea pigs from Ebola at 18 months post-immunization.

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Glycoprotein-specific IgG antibody responses are indicative of induced protection.

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Results support further long-term protection studies in nonhuman primates.

Ebola virus (EBOV) infections cause lethal hemorrhagic fever in humans, resulting in up to 90% mortality. EBOV outbreaks are sporadic and unpredictable in nature; therefore, a vaccine that is able to provide durable immunity is needed to protect those who are at risk of exposure to the virus. This study assesses the long-term efficacy of the vesicular stomatitis virus (VSV)-based vaccine (VSVΔG/EBOVGP) in two rodent models of EBOV infection. Mice and guinea pigs were first immunized with 2 × 10⁴ or 2 × 10⁵ plaque forming units (PFU) of VSVΔG/EBOVGP, respectively. Challenge of mice with a lethal dose of mouse-adapted EBOV (MA-EBOV) at 6.5 and 9 months after vaccination provided complete protection, and 80% (12 of 15 survivors) protection at 12 months after vaccination. Challenge of guinea pigs with a lethal dose of guinea pig-adapted EBOV (GA-EBOV) at 7, 12 and 18 months after vaccination resulted in 83% (5 of 6 survivors) at 7 months after vaccination, and 100% survival at 12 and 18 months after vaccination. No weight loss or clinical signs were observed in the surviving animals. Antibody responses were analyzed using sera from individual rodents. Levels of EBOV glycoprotein-specific IgG antibody measured immediately before challenge appeared to correlate with protection. These studies confirm that vaccination with VSVΔG/EBOVGP is able to confer long-term protection against Ebola infection in mice and guinea pigs, and support follow-up studies in non-human primates.

Virus-vectored influenza virus vaccines

Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans, comparing them to licensed vaccines and the hurdles faced for licensure of these next-generation influenza virus vaccines.

The profile of tumor antigens which can be targeted by immunotherapy depends upon the tumor's anatomical site

Previously, we showed that vesicular stomatitis virus (VSV) engineered to express a cDNA library from human melanoma cells (ASMEL, Altered Self Melanoma Epitope Library) was an effective systemic therapy to treat subcutaneous (s.c.) murine B16 melanomas. Here, we show that intravenous treatment with the same ASMEL VSV-cDNA library was an effective treatment for established intra-cranial (i.c.) melanoma brain tumors. The optimal combination of antigens identified from the ASMEL which treated s.c. B16 tumors (VSV-N-RAS+VSV-CYTC-C+VSV-TYRP-1) was ineffective against i.c. B16 brain tumors. In contrast, combination of VSV-expressed antigens-VSV-HIF-2α+VSV-SOX-10+VSV-C-MYC+VSV-TYRP1-from ASMEL which was highly effective against i.c. B16 brain tumors, had no efficacy against the same tumors growing subcutaneously. Correspondingly, i.c. B16 tumors expressed a HIF-2α(Hi), SOX-10(Hi), c-myc(Hi), TYRP1, N-RAS(lo)Cytc(lo) antigen profile, which differed significantly from the HIF-2α(lo), SOX-10(lo), c-myc(lo), TYRP1, N-RAS(Hi)Cytc(Hi) phenotype of s.c. B16 tumors, and was imposed upon the tumor cells by CD11b(+) cells within the local brain tumor microenvironment. Combining T-cell costimulation with systemic VSV-cDNA treatment, long-term cures of mice with established i.c. tumors were achieved in about 75% of mice. Our data show that the anatomical location of a tumor profoundly affects the profile of antigens that it expresses.

VSV-GP: a potent viral vaccine vector that boosts the immune response upon repeated applications

Antivector immunity limits the response to homologous boosting for viral vector vaccines. Here, we describe a new, potent vaccine vector based on replication-competent vesicular stomatitis virus pseudotyped with the glycoprotein of the lymphocytic choriomeningitis virus (VSV-GP), which we previously showed to be safe in mice. In mice, VSV and VSV-GP encoding ovalbumin (OVA) as a model antigen (VSV-OVA and VSV-GP-OVA) induced equal levels of OVA-specific humoral and cellular immune responses upon a single immunization. However, boosting with the same vector was possible only for VSV-GP-OVA as neutralizing antibodies to VSV limited the immunogenicity of the VSV-OVA boost. OVA-specific cytotoxic T-lymphocyte (CTL) responses induced by VSV-GP-OVA were at least as potent as those induced by an adenoviral state-of-the-art vaccine vector and completely protected mice in a Listeria monocytogenes challenge model. VSV-GP is so far the only replication-competent vaccine vector that does not lose efficacy upon repeated application.

IMPORTANCE

Although there has been great progress in treatment and prevention of infectious diseases in the past several years, effective vaccines against some of the most serious infections, e.g., AIDS, malaria, hepatitis C, or tuberculosis, are urgently needed. Here, several approaches based on viral vector vaccines are under development. However, for all viral vaccine vectors currently in clinical testing, repeated application is limited by neutralizing antibodies to the vector itself. Here, we have exploited the potential of vesicular stomatitis virus pseudotyped with the glycoprotein of the lymphocytic choriomeningitis virus (VSV-GP) as a vaccine platform. VSV-GP is the first replication-competent viral vector vaccine that does not induce vector-specific humoral immunity, i.e., neutralizing antibodies, and therefore can boost immune responses against a foreign antigen by repeated applications. The vector allows introduction of various antigens and therefore can serve as a platform technology for the development of novel vaccines against a broad spectrum of diseases.

Single-dose live-attenuated Nipah virus vaccines confer complete protection by eliciting antibodies directed against surface glycoproteins

BACKGROUND

Nipah virus (NiV), a zoonotic pathogen causing severe respiratory illness and encephalitis in humans, emerged in Malaysia in 1998 with subsequent outbreaks on an almost annual basis since 2001 in parts of the Indian subcontinent. The high case fatality rate, human-to-human transmission, wide-ranging reservoir distribution and lack of licensed intervention options are making NiV a serious regional and potential global public health problem. The objective of this study was to develop a fast-acting, single-dose NiV vaccine that could be implemented in a ring vaccination approach during outbreaks.

METHODS

In this study we have designed new live-attenuated vaccine vectors based on recombinant vesicular stomatitis viruses (rVSV) expressing NiV glycoproteins (G or F) or nucleoprotein (N) and evaluated their protective efficacy in Syrian hamsters, an established NiV animal disease model. We further characterized the humoral immune response to vaccination in hamsters using ELISA and neutralization assays and performed serum transfer studies.

RESULTS

Vaccination of Syrian hamsters with a single dose of the rVSV vaccine vectors resulted in strong humoral immune responses with neutralizing activities found only in those animals vaccinated with rVSV expressing NiV G or F proteins. Vaccinated animals with neutralizing antibody responses were completely protected from lethal NiV disease, whereas animals vaccinated with rVSV expressing NiV N showed only partial protection. Protection of NiV G or F vaccinated animals was conferred by antibodies, most likely the neutralizing fraction, as demonstrated by serum transfer studies. Protection of N-vaccinated hamsters was not antibody-dependent indicating a role of adaptive cellular responses for protection.

CONCLUSIONS

The rVSV vectors expressing Nipah virus G or F are prime candidates for new 'emergency vaccines' to be utilized for NiV outbreak management.

Long-term single-dose efficacy of a vesicular stomatitis virus-based Andes virus vaccine in Syrian hamsters

Andes virus (ANDV) is highly pathogenic in humans and is the primary etiologic agent of hantavirus cardiopulmonary syndrome (HCPS) in South America. Case-fatality rates are as high as 50% and there are no approved vaccines or specific therapies for infection. Our laboratory has recently developed a replication-competent recombinant vesicular stomatitis virus (VSV)-based vaccine that expressed the glycoproteins of Andes virus in place of the native VSV glycoprotein (G). This vaccine is highly efficacious in the Syrian hamster model of HCPS when given 28 days before challenge with ANDV, or when given around the time of challenge (peri-exposure), and even protects when administered post-exposure. Herein, we sought to test the durability of the immune response to a single dose of this vaccine in Syrian hamsters. This vaccine was efficacious in hamsters challenged intranasally with ANDV 6 months after vaccination (p = 0.025), but animals were not significantly protected following 1 year of vaccination (p = 0.090). The decrease in protection correlated with a reduction of measurable neutralizing antibody responses, and suggests that a more robust vaccination schedule might be required to provide long-term immunity.

Signaling pathways in murine dendritic cells that regulate the response to vesicular stomatitis virus vectors that express flagellin

Vesicular stomatitis virus (VSV) vectors that express heterologous antigens have shown promise as vaccines in preclinical studies. The efficacy of VSV-based vaccines can be improved by engineering vectors that enhance innate immune responses. We previously generated a VSV vaccine vector that incorporates two enhancing strategies: an M protein mutation (M51R) that prevents the virus from suppressing host antiviral responses and a gene encoding bacterial flagellin (M51R-F vector). The rationale was that intracellular expression of flagellin would activate innate immune pathways in addition to those activated by virus alone. This was tested with dendritic cells (DCs) from mice containing deletions in key signaling molecules. Infection of DC with either M51R or M51R-F vector induced the production of interleukin-12 (IL-12) and IL-6 and increased surface expression of T cell costimulatory molecules. These responses were dramatically reduced in DCs from IPS-1(-/-) mice. Infection with M51R-F vector also induced the production of IL-1β. In addition, in approximately half of the DCs, M51R-F vector induced pyroptosis, a proinflammatory-type of cell death. These responses to flagellin were ablated in DCs from NLRC4(-/-) mice but not Toll-like receptor 5-deficient (TLR5(-/-)) mice, indicating that they resulted from inflammasome activation. These results demonstrate that flagellin induces additional innate immune mechanisms over those induced by VSV alone.

Immunobiology of influenza vaccines

Vaccination is the primary strategy for prevention and control of influenza. The surface hemagglutinin (HA) protein of the influenza virus contains two structural elements (head and stalk) that differ in their potential utility as vaccine targets. The head of the HA protein is the primary target of antibodies that confer protective immunity to influenza viruses. The underlying health status, age, and gene polymorphisms of vaccine recipients and, just as importantly, the extent of the antigenic match between the viruses in the vaccine and those that are circulating modulate influenza vaccine protection. Vaccine adjuvants and live attenuated influenza vaccine improve the breadth of immunity to seasonal and pandemic virus strains. Eliciting antibodies against the conserved HA stem region that cross-react with HAs within influenza virus types or subtypes would allow for the development of a universal influenza vaccine. The highly complex network of interactions generated after influenza infection and vaccination can be studied with the use of systems biology tools, such as DNA microarray chips. The use of systems vaccinology has allowed for the generation of gene expression signatures that represent key transcriptional differences between asymptomatic and symptomatic host responses to influenza infection. Additionally, the use of systems vaccinology tools have resulted in the identification of novel surrogate gene markers that are predictors of the magnitude of host responses to vaccines, which is critical to both vaccine development and public health. Identifying associations between variations in vaccine immune responses and gene polymorphisms is critical in the development of universal influenza vaccines.

Experimental vaccines against potentially pandemic and highly pathogenic avian influenza viruses

Influenza A viruses continue to emerge and re-emerge, causing outbreaks, epidemics and occasionally pandemics. While the influenza vaccines licensed for public use are generally effective against seasonal influenza, issues arise with production, immunogenicity, and efficacy in the case of vaccines against pandemic and emerging influenza viruses, and highly pathogenic avian influenza virus in particular. Thus, there is need of improved influenza vaccines and vaccination strategies. This review discusses advances in alternative influenza vaccines, touching briefly on licensed vaccines and vaccine antigens; then reviewing recombinant subunit vaccines, virus-like particle vaccines and DNA vaccines, with the main focus on virus-vectored vaccine approaches.

Long-term vaccine-induced heterologous protection against H5N1 influenza viruses in the ferret model

Please cite this paper as: Ducatez et al. (2012) Long‐term vaccine‐induced heterologous protection against H5N1 influenza viruses in the ferret model. Influenza and Other Respiratory Viruses 7(4), 506–512.

Background  Highly pathogenic H5N1 influenza viruses reemerged in humans in 2003 and have caused fatal human infections in Asia and Africa as well as ongoing outbreaks in poultry. These viruses have evolved substantially and are now so antigenically varied that a single vaccine antigen may not protect against all circulating strains. Nevertheless, studies have shown that substantial cross‐reactivity can be achieved with H5N1 vaccines. These studies have not, however, addressed the issue of duration of such cross‐reactive protection.

Objectives  To directly address this using the ferret model, we used two recommended World Health Organization H5N1 vaccine seed strains – A/Vietnam/1203/04 (clade 1) and A/duck/Hunan/795/02 (clade 2.1) – seven single, double, or triple mutant viruses based on A/Vietnam/1203/04, and the ancestral viruses A and D, selected from sequences at nodes of the hemagglutinin and neuraminidase gene phylogenies to represent antigenically diverse progeny H5N1 subclades as vaccine antigens.

Results  All inactivated whole‐virus vaccines provided full protection against morbidity and mortality in ferrets challenged with the highly pathogenic H5N1 strain A/Vietnam/1203/04 5 months and 1 year after immunization.

Conclusion  If an H5N1 pandemic was to arise, and with the hypothesis that one can extrapolate the results from three doses of a whole‐virion vaccine in ferrets to the available split vaccines for use in humans, the population could be efficiently immunized with currently available H5N1 vaccines, while the homologous vaccine is under production.

A cell culture-derived whole-virus H5N1 vaccine induces long-lasting cross-clade protective immunity in mice which is augmented by a homologous or heterologous booster vaccination

BACKGROUND

Preparation for an H5N1 influenza pandemic in humans could include priming the population in the pre-pandemic period with a vaccine produced from an existing H5N1 vaccine strain, with the possibility of boosting with a pandemic virus vaccine when it becomes available. We investigated the longevity of the immune response after one or two priming immunizations with a whole-virus H5N1 vaccine and the extent to which this can be boosted by later immunization with either a homologous or heterologous vaccine.

METHODS

Mice received one or two priming immunizations with a Vero cell culture-derived, whole-virus clade 1 H5N1 vaccine formulated to contain either 750 ng or 30 ng hemagglutinin. Six months after the first priming immunization, mice received either a booster immunization with the same clade 1 vaccine or a heterologous clade 2.1 vaccine, or buffer. Humoral and cellular immune responses were evaluated before and at regular intervals after immunizations. Three weeks after booster immunization, mice were challenged with a lethal dose of wild-type H5N1 virus from clades 1, 2.1 or 2.2 and survival was monitored for 14 days.

RESULTS

One or two priming immunizations with the 750 ng or 30 ng HA formulations, respectively, induced H5N1-neutralizing antibody titers which were maintained for ≥ 6 months and provided long-term cross-clade protection against wild-type virus challenge. Both humoral and cellular immune responses were substantially increased by a booster immunization after 6 months. The broadest protective immunity was provided by an immunization regimen consisting of one or two priming immunizations with a clade 1 vaccine and a boosting immunization with a clade 2.1 vaccine.

CONCLUSIONS

These data support the concept that pre-pandemic vaccination can provide robust and long-lasting H5N1 immunity which could be effectively boosted by immunization either with another pre-pandemic vaccine or with the pandemic strain vaccine.

New strategies for the development of H5N1 subtype influenza vaccines: progress and challenges

The emergence and spread of highly pathogenic avian influenza (H5N1) viruses among poultry in Asia, the Middle East, and Africa have fueled concerns of a possible human pandemic, and spurred efforts towards developing vaccines against H5N1 influenza viruses, as well as improving vaccine production methods. In recent years, promising experimental reverse genetics-derived H5N1 live attenuated vaccines have been generated and characterized, including vaccines that are attenuated through temperature-sensitive mutation, modulation of the interferon antagonist protein, or disruption of the M2 protein. Live attenuated influenza virus vaccines based on each of these modalities have conferred protection against homologous and heterologous challenge in animal models of influenza virus infection. Alternative vaccine strategies that do not require the use of live virus, such as virus-like particle (VLP) and DNA-based vaccines, have also been vigorously pursued in recent years. Studies have demonstrated that influenza VLP vaccination can confer homologous and heterologous protection from lethal challenge in a mouse model of infection. There have also been improvements in the formulation and production of vaccines following concerns over the threat of H5N1 influenza viruses. The use of novel substrates for the growth of vaccine virus stocks has been intensively researched in recent years, and several candidate cell culture-based systems for vaccine amplification have emerged, including production systems based on Madin-Darby canine kidney, Vero, and PerC6 cell lines. Such systems promise increased scalability of product, and reduced reliance on embryonated chicken eggs as a growth substrate. Studies into the use of adjuvants have shown that oil-in-water-based adjuvants can improve the immunogenicity of inactivated influenza vaccines and conserve antigen in such formulations. Finally, efforts to develop more broadly cross-protective immunization strategies through the inclusion of conserved influenza virus antigens in vaccines have led to experimental vaccines based on the influenza hemagglutinin (HA) stem domain. Such vaccines have been shown to confer protection from lethal challenge in mouse models of influenza virus infection. Through further development, vaccines based on the HA stem have the potential to protect vaccinated individuals against unanticipated pandemic and epidemic influenza virus strains. Overall, recent advances in experimental vaccines and in vaccine production processes provide the potential to lower mortality and morbidity resulting from influenza infection.

Using virally expressed melanoma cDNA libraries to identify tumor-associated antigens that cure melanoma

Multiple intravenous injections of a cDNA library, derived from human melanoma cell lines and expressed using the highly immunogenic vector vesicular stomatitis virus (VSV), cured mice with established melanoma tumors. Successful tumor eradication was associated with the ability of mouse lymphoid cells to mount a tumor-specific CD4(+) interleukin (IL)-17 recall response in vitro. We used this characteristic IL-17 response to screen the VSV-cDNA library and identified three different VSV-cDNA virus clones that, when used in combination but not alone, achieved the same efficacy against tumors as the complete parental virus library. VSV-expressed cDNA libraries can therefore be used to identify tumor rejection antigens that can cooperate to induce anti-tumor responses. This technology should be applicable to antigen discovery for other cancers, as well as for other diseases in which immune reactivity against more than one target antigen contributes to disease pathology.

Vesicular stomatitis virus-based vaccine protects hamsters against lethal challenge with Andes virus

Andes virus (ANDV) is a highly pathogenic South American hantavirus that causes hantavirus pulmonary syndrome (HPS). A high case fatality rate, the potential for human-to-human transmission, the capacity to infect via aerosolization, and the absence of effective therapies make it imperative that a safe, fast-acting, and effective ANDV vaccine be developed. We generated and characterized a recombinant vesicular stomatitis virus (VSV) vector expressing the ANDV surface glycoprotein precursor (VSVΔG/ANDVGPC) as a possible vaccine candidate and tested its efficacy in the only lethal-disease animal model of HPS. Syrian hamsters immunized with a single injection of VSVΔG/ANDVGPC were fully protected against disease when challenged at 28, 14, 7, or 3 days postimmunization with a lethal dose of ANDV; however, the mechanism of protection seems to differ depending on when the immunization occurs. At 28 days postimmunization, a lack of detectable ANDV RNA in lung, liver, and blood tissue samples, as well as a lack of seroconversion to the ANDV nucleocapsidprotein in nearly all animals, suggested largely sterile immunity. The vaccine was able to generate high levels of neutralizing anti-ANDV G(N)/G(C) antibodies, which seem to play a role as a mechanism of vaccine protection. Administration of the vaccine at 7 or 3 days before challenge also resulted in full protection but with no specific neutralizing humoral immune response, suggesting a possible role of innate responses in protection against challenge virus replication. Administration of the vaccine 24 h postchallenge was successful in protecting 90% of hamsters and again suggested the induction of a potent antiviral state by the recombinant vector as a potential mechanism. Overall, our data suggest the potential for the use of the VSV platform as a fast-acting and effective prophylaxis/postexposure treatment against lethal hantavirus infections.

Broad antigenic coverage induced by vaccination with virus-based cDNA libraries cures established tumors

Effective cancer immunotherapy requires the release of a broad spectrum of tumor antigens in the context of potent immune activation. We show here that a cDNA library of normal tissue, expressed from a highly immunogenic viral platform, cures established tumors of the same histological type from which the cDNA library was derived. Immune escape occurred with suboptimal vaccination, but tumor cells that escaped the immune pressure were readily treated by second-line virus-based immunotherapy. This approach has several major advantages. Use of the cDNA library leads to presentation of a broad repertoire of (undefined) tumor-associated antigens, which reduces emergence of treatment-resistant variants and also permits rational, combined-modality approaches in the clinic. Finally, the viral vectors can be delivered systemically, without the need for tumor targeting, and are amenable to clinical-grade production. Therefore, virus-expressed cDNA libraries represent a novel paradigm for cancer treatment addressing many of the key issues that have undermined the efficacy of immuno- and virotherapy to date.

Mutations in the glycoprotein of vesicular stomatitis virus affect cytopathogenicity: potential for oncolytic virotherapy

Vesicular stomatitis virus (VSV) has been widely used to characterize cellular processes, viral resistance, and cytopathogenicity. Recently, VSV has also been used for oncolytic virotherapy due to its capacity to selectively lyse tumor cells. Mutants of the matrix (M) protein of VSV have generally been preferred to the wild-type virus for oncolysis because of their ability to induce type I interferon (IFN) despite causing weaker cytopathic effects. However, due to the large variability of tumor types, it is quite clear that various approaches and combinations of multiple oncolytic viruses will be needed to effectively treat most cancers. With this in mind, our work focused on characterizing the cytopathogenic profiles of four replicative envelope glycoprotein (G) VSV mutants. In contrast to the prototypic M mutant, VSV G mutants are as efficient as wild-type virus at inhibiting cellular transcription and host protein translation. Despite being highly cytopathic, the mutant G(6R) triggers type I interferon secretion as efficiently as the M mutant. Importantly, most VSV G mutants are more effective at killing B16 and MC57 tumor cells in vitro than the M mutant or wild-type virus through apoptosis induction. Taken together, our results demonstrate that VSV G mutants retain the high cytopathogenicity of wild-type VSV, with G(6R) inducing type I IFN secretion at levels similar to that of the M mutant. VSV G protein mutants could therefore prove to be highly valuable for the development of novel oncolytic virotherapy strategies that are both safe and efficient for the treatment of various types of cancer.

Vesicular stomatitis virus-based H5N1 avian influenza vaccines induce potent cross-clade neutralizing antibodies in rhesus macaques

We analyzed the ability of a vaccine vector based on vesicular stomatitis virus (VSV) to induce a neutralizing antibody (NAb) response to avian influenza viruses (AIVs) in rhesus macaques. Animals vaccinated with vectors expressing either strain A/Hong Kong/156/1997 or strain A/Vietnam/1203/2004 H5 hemagglutinin (HA) were able to generate robust NAb responses. The ability of the vectors to induce NAbs against homologous and heterologous AIVs after a single dose was dependent upon the HA antigen incorporated into the VSV vaccine. The vectors expressing strain A/Vietnam/1203/2004 H5 HA were superior to those expressing strain A/Hong Kong/156/1997 HA at inducing cross-clade NAbs.

Progress in filovirus vaccine development: evaluating the potential for clinical use

Marburg and Ebola viruses cause severe hemorrhagic fever in humans and nonhuman primates. Currently, there are no effective treatments and no licensed vaccines; although a number of vaccine platforms have proven successful in animal models. The ideal filovirus vaccine candidate should be able to provide rapid protection following a single immunization, have the potential to work postexposure and be cross-reactive or multivalent against all Marburg virus strains and all relevant Ebola virus species and strains. Currently, there are multiple platforms that have provided prophylactic protection in nonhuman primates, including DNA, recombinant adenovirus serotype 5, recombinant human parainfluenza virus 3 and virus-like particles. In addition, a single platform, recombinant vesicular stomatitis virus, has demonstrated both prophylactic and postexposure protection in nonhuman primates. These results demonstrate that achieving a vaccine that is protective against filoviruses is possible; the challenge now is to prove its safety and efficacy in order to obtain a vaccine that is ready for human use.