Genetic and subunit vaccines based on the stem domain of the equine influenza hemagglutinin provide homosubtypic protection against heterologous strains

H3N8 influenza virus strains have been associated with infectious disease in equine populations throughout the world. Although current vaccines for equine influenza stimulate a protective humoral immune response against the surface glycoproteins, disease in vaccinated horses has been frequently reported, probably due to poor induction of cross-reactive antibodies against non-matching strains. This work describes the performance of a recombinant protein vaccine expressed in prokaryotic cells (ΔHAp) and of a genetic vaccine (ΔHAe), both based on the conserved stem region of influenza hemagglutinin (HA) derived from A/equine/Argentina/1/93 (H3N8) virus.Sera from mice inoculated with these immunogens in different combinations and regimes presented reactivity in vitro against highly divergent influenza virus strains belonging to phylogenetic groups 1 and 2 (H1 and H3 subtypes, respectively), and conferred robust protection against a lethal challenge with both the homologous equine strain (100%) and the homosubtypic human strain A/Victoria/3/75 (H3N2) (70–100%). Animals vaccinated with the same antigens but challenged with the human strain A/PR/8/34 (H1N1), belonging to the phylogenetic group 1, were not protected (0–33%). Combination of protein and DNA immunogens showed higher reactivity to non-homologous strains than protein alone, although all vaccines were permissive for lung infection.     

Protective immune responses induced by different recombinant vaccine regimes to Rift Valley fever

The glycoprotein (GP) and nucleocapsid (NC) genes of Rift Valley fever virus (RVFV) were expressed in different expression systems and were evaluated for their ability to protect mice from virulent challenge using a prime-boost regime. Mice vaccinated with a lumpy skin disease virus-vectored recombinant vaccine (rLSDV-RVFV) expressing the two RVFV glycoproteins (G1 and G2) developed neutralising antibodies and were fully protected when challenged, as were those vaccinated with a crude extract of truncated G2 glycoprotein (tG2). By contrast mice vaccinated with a DNA vaccine expressing G1 and G2 did not sero-convert with only 20% of them surviving challenge. Mice vaccinated with the DNA vaccine and boosted with rLSDV-RVFV also failed to sero-convert but 40% survived challenge. Surprisingly, although none of the mice immunised with the purified NC protein sero-converted, 60% of them survived virulent challenge. The rLSDV-RVFV construct was then further evaluated in sheep for its dual protective abilities against RVFV and sheeppox virus (SPV). Vaccinated sheep sero-converted for both viruses and were protected against RVFV challenge, however, neither the immunised or negative control animals showed any significant reactions to the virulent SPV challenge.     

Virus-like particle vaccine induces cross-protection against human metapneumovirus infections in mice

Human metapneumovirus (HMPV) is a paramyxovirus that causes acute respiratory-tract infections in children and adults worldwide. A safe and effective vaccine could decrease the burden of disease associated with this novel pathogen. We engineered HMPV viral-like particles (HMPV-VLPs) derived from retroviral core particles that mimic the properties of the viral surface of two HMPV viruses of either lineage A or B. These VLPs functionally display F and G HMPV surface glycoproteins. When injected in mice, HMPV-VLPs induce strong humoral immune response against both homologous and heterologous strains. Moreover, the induced neutralizing antibodies prevented mortality upon subsequent infection of the lungs with both homologous and heterologous viruses. Upon challenge, viral titers in the lungs of immunized animals were significantly reduced as compared to those of control animals. In conclusion, a HMPV-VLP vaccine that induces cross-protective immunity in mice is a promising approach to prevent HMPV infections.     

Evaluation of ISCOM-adjuvanted subunit vaccines containing recombinant feline immunodeficiency virus Rev, OrfA and envelope protein in cats

For the development of feline immunodeficiency virus (FIV) vaccines mostly structural proteins have been evaluated for their capacity to induce protective immunity. In the present study, subunit vaccines containing recombinant FIV accessory proteins Rev and OrfA were evaluated in cats. Cats were vaccinated repeatedly with these proteins, adjuvanted with immune stimulating complexes (ISCOMs). In addition, cats were vaccinated with bacterially expressed fragments spanning the entire FIV envelope protein, either alone or in combination with the regulatory proteins. Subsequently, the cats were challenged with a homologous FIV strain to assess the level of protective immunity achieved with the respective vaccination regimens. Although the vaccines proved to be immunogenic, vaccinated cats were not protected from infection with FIV.     

Vaccination of aged mice with adjuvanted recombinant influenza nucleoprotein enhances protective immunity

Elderly individuals are highly susceptible to influenza virus (IAV) infection and respond poorly to influenza vaccines. Although the generally accepted correlate of protection following influenza vaccination is neutralizing antibody titers, cytotoxic T cell activity has been found to be a better correlate in the elderly. This suggests that vaccines designed to protect against influenza in the elderly should induce both humoral and cellular immunity. The co-induction of T cell immunity is additionally advantageous, as virus-specific T cells are frequently cross-reactive against different strains of IAV. Here, we tested the capacity of a synthetic TLR-4 adjuvant, SLA-SE (second-generation lipid adjuvant formulated in a squalene-based oil-in-water emulsion) to elicit T cell immunity to a recombinant influenza nucleoprotein (rNP), in both young and aged mice. IAV challenge of vaccinated mice resulted in a modest increase in the numbers of NP-specific CD4 and CD8 effector T cells in the spleen, but did not increase numbers of memory phenotype CD8 T cells generated following viral clearance (compared to control vaccinated mice). Cytotoxic activity of CD8, but not CD4 T cells was increased. In addition, SLA-SE adjuvanted vaccination specifically enhanced the production of NP-specific IgG2c antibodies in both young and aged mice. Although NP-specific antibodies are not neutralizing, they can cooperate with CD8 T cells and antigen-presenting cells to enhance protective immunity. Importantly, SLA-SE adjuvanted rNP-vaccination of aged mice resulted in significantly enhanced viral clearance. In addition, vaccination of aged mice resulted in enhanced survival after lethal challenge compared to control vaccination, that approached statistical significance. These data demonstrate the potential of SLA-SE adjuvanted rNP vaccines to (i) generate both cellular and humoral immunity to relatively conserved IAV proteins and (ii) elicit protective immunity to IAV in aged mice.     

Intranasal vaccination induced cross-protective secretory IgA antibodies against SARS-CoV-2 variants with reducing the potential risk of lung eosinophilic immunopathology

To control the coronavirus disease 2019 (COVID-19) pandemic, there is a need to develop vaccines to prevent infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. One candidate is a nasal vaccine capable of inducing secretory IgA antibodies in the mucosa of the upper respiratory tract, the initial site of infection. However, regarding the development of COVID-19 vaccines, there is concern about the potential risk of inducing lung eosinophilic immunopathology as a vaccine-associated enhanced respiratory disease as a result of the T helper 2 (Th2)-dominant adaptive immune response. In this study, we investigated the protective effect against virus infection induced by intranasal vaccination of recombinant trimeric spike protein derived from SARS-CoV-2 adjuvanted with CpG oligonucleotides, ODN2006, in mouse model. The intranasal vaccine combined with ODN2006 successfully induced not only systemic spike-specific IgG antibodies, but also secretory IgA antibodies in the nasal mucosa. Secretory IgA antibodies showed high protective ability against SARS-CoV-2 variants (Alpha, Beta and Gamma variants) compared to IgG antibodies in the serum. The nasal vaccine of this formulation induced a high number of IFN-γ-secreting cells in the draining cervical lymph nodes and a lower spike-specific IgG1/IgG2a ratio compared to that of subcutaneous vaccination with alum as a typical Th2 adjuvant. These features are consistent with the induction of the Th1 adaptive immune response. In addition, mice intranasally vaccinated with ODN2006 showed less lung eosinophilic immunopathology after viral challenge than mice subcutaneously vaccinated with alum adjuvant. Our findings indicate that intranasal vaccine adjuvanted with ODN2006 could be a candidate that can prevent the infection of antigenically different variant viruses, reducing the risk of vaccine-associated enhanced respiratory disease.     

Evaluation of attenuated VSVs with mutated M or/and G proteins as vaccine vectors

Vesicular stomatitis virus (VSV) is a promising vector for vaccine and oncolysis, but it can also produce acute diseases in cattle, horses, and swine characterized by vesiculation and ulceration of the tongue, oral tissues, feet, and teats. In experimental animals (primates, rats, and mice), VSV has been shown to lead to neurotoxicities, such as hind limb paralysis. The virus matrix protein (M) and glycoprotein (G) are both major pathogenic determinants of wild-type VSV and have been the major targets for the production of attenuated strains. Existing strategies for attenuation included: (1) deletion or M51R substitution in the M protein (VSVΔM51 or VSVM51R, respectively); (2) truncation of the C-terminus of the G protein (GΔ28). Despite these mutations, recombinant VSV with mutated M protein is only moderately attenuated in animals, whereas there are no detailed reports to determine the pathogenicity of recombinant VSV with truncated G protein at high dose. Thus, a novel recombinant VSV (VSVΔM51-GΔ28) as well as other attenuated VSVs (VSVΔM51, VSV-GΔ28) were produced to determine their efficacy as vaccine vectors with low pathogenicity. In vitro studies indicated that truncated G protein (GΔ28) could play a more important role than deletion of M51 (ΔM51) for attenuation of recombinant VSV. VSVΔM51-GΔ28 was determined to be the most attenuated virus with low pathogenicity in mice, with VSV-GΔ28 also showing relatively reduced pathogenicity. Further, neutralizing antibodies stimulated by VSV-GΔ28 proved to be significantly higher than in mice treated with VSVΔM51-GΔ28. In conclusion, among different attenuated VSVs with mutated M and/or G proteins, recombinant VSV with only truncated G protein (VSV-GΔ28) demonstrated ideal balance between pathogenesis and stimulating a protective immune response. These properties make VSV-GΔ28 a promising vaccine vector and vaccine candidate for preventing vesicular stomatitis disease.     

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.     

Immunization with plasmid DNA expressing the caprine arthritis-encephalitis virus envelope gene: quantitative and qualitative aspects of antibody response to viral surface glycoprotein

Saanen goats were vaccinated intradermally with plasmid DNA expressing caprine arthritis-encephalitis virus (CAEV) rev-env (pENV) or tat-rev-env (pTAT-ENV) or vaccinia virus expressing CAEV env (rWR-63). Sera from all vaccinated goats immunoprecipitated CAEV surface (SU) and transmembrane (TM) glycoproteins with a dominant response to SU. Antibody response to CAEV SU induced by plasmid DNA was relatively biased toward IgG2, whereas vaccinia rWR-63 induced predominantly IgG1 antibodies to SU. Differential IgG isotype bias established by immunization with plasmid or vaccinia vectors was maintained following subcutaneous boost with purified CAEV SU in Freund's incomplete adjuvant (FIA). Goats injected with pUC18 control plasmid followed by immunization with SU-FIA also had IgG2 biased responses, whereas SU-FIA immunization of a goat primed with vaccinia rWR-SC11 without the CAEV env gene induced a predominant IgG1 response. We conclude that pUC based plasmids expressing the CAEV env gene promote stable type 1 biased immune responses to plasmid encoded SU. IgG2 biased response may be due to innate type 1 priming capacity of immunostimulatory CpG motifs in the pUC ampicillin resistance gene.     

Evaluation in chimpanzees of vaccinia virus recombinants that express the surface glycoproteins of human respiratory syncytial virus

The immunogenicity and protective efficacy of recombinant vaccinia viruses that express the two major protective antigens of human respiratory syncytial virus (RSV), the F and G glycoproteins, were evaluated in chimpanzees. In previous studies in rodents and monkeys the F and G proteins expressed by the same recombinants were highly immunogenic and induced high levels of resistance to RSV replication following subsequent challenge. In contrast, in chimpanzees, a single intradermal immunization induced only moderate levels of F and G-specific serum antibodies as measured by an enzyme-linked immunosorbent assay, and these antibodies did not efficiently neutralize RSV infectivity in vitro. This poor antibody response in chimpanzees to the F and G glycoproteins occurred despite efficient replication of the vaccinia virus vector as evidenced by lesion size and serum antibody response to vaccinia virus. Upon intranasal RSV challenge, it was observed that prior immunization with the F and G recombinants effected only a marginal reduction in the magnitude and duration of RSV shedding from the nose and trachea and did not reduce illness. However, the RSV challenge induced a strong secondary antibody response, resulting in very high titres (greater than 8000 reciprocal mean titre) of serum neutralizing antibodies. The poor protective efficacy observed here is discussed with regard to the permissiveness of the chimpanzee to RSV replication, the general requirements for effective immunization against RSV, and the limitations of experimental animals for evaluating candidate RSV vaccines.     

Fc functional antibody responses to adjuvanted versus unadjuvanted seasonal influenza vaccination in community-dwelling older adults

BackgroundSeasonal influenza vaccination with a standard trivalent influenza vaccine (TIV) induces a modest, and cross-reactive, Fc functional antibody response in older adults. Recent improvements to influenza vaccines include a quadrivalent influenza vaccine (QIV) and a TIV adjuvanted with the squalene-based oil-in-water emulsion MF59.MethodsPre- and post-vaccination serum samples from older adults vaccinated with QIV (n = 27) and adjuvanted TIV (n = 44) were studied using hemagglutination inhibition (HAI) assays and dimeric Fc-gamma receptor IIIa binding ELISAs, as a surrogate of antibody-dependent cellular cytotoxicity (ADCC).ResultsWe found that the unadjuvanted QIV elicited a stronger HAI response against the H1N1 vaccine virus than the adjuvanted TIV. Post-vaccination levels of HA-specific ADCC antibodies were similar for older adults vaccinated with QIV and adjuvanted TIV. The ADCC response to influenza vaccination was largely determined by pre-vaccination or baseline levels of these antibodies, with older adults with low baseline levels of ADCC activity demonstrating greater post-vaccination rises.ConclusionsIn this cohort of community-dwelling older adults, the QIV was at least as good as the adjuvanted TIV in the induction of ADCC and HAI responses. Further studies on how these antibody responses translate to efficacy in preventing influenza infections are warranted.     

Impact of pre-existing immunity on the induction of functional cross-reactive anti-hemagglutinin stalk antibodies following vaccination with an AS03 adjuvanted pandemic H1N1 vaccine

The 2009 pandemic H1N1 (A(H1N1)pdm09) virus had a highly divergent hemagglutinin (HA) compared to pre-2009 seasonal H1N1 strains. Most peoples were immunologically naïve to the A(H1N1)pdm09, although hospital workers were exposed early in the pandemic before pandemic vaccines became available. Here, we evaluated how pre-existing antibodies influence the induction of cross-functional HA stalk antibodies following A(H1N1)pdm09 vaccination.Fifty-six healthcare workers vaccinated with AS03 adjuvanted A(H1N1)pdm09 vaccine were chosen by their pre-vaccination priming status (primed HI titers ≥ 40 or unprimed < 40). We analyzed the HA head- and stalk-specific serum IgG subclasses at pre- and 21 days post-vaccination. We also assessed the functionality of the HA stalk-specific antibodies to neutralize virus and mediate antibody dependent cellular cytotoxicity (ADCC).Primed individuals had higher pre-existing HA head- and stalk-specific IgG1, as well as higher ADCC functionality of stalk antibodies. However, following vaccination with the adjuvanted pandemic vaccine, only the quantity of HA head specific IgG1 antibodies were significantly higher than in unprimed individuals. The priming status did not impact upon the cross-reactive HA stalk specific IgG antibodies or their ability to neutralize virus or induce ADCC post-vaccination. In conclusion, a single dose of AS03 adjuvanted pandemic vaccine elicited similar levels of functional antibodies in naïve and primed individuals. These findings are important for understanding the immunological factors that impact or modulate pandemic vaccine responses in humans.     

Immunogenic properties of RSV-B1 fusion (F) protein gene-encoding recombinant adenoviruses

Two recombinant adenoviruses designated rAd-F0ΔTM and rAd-F0 carrying the transmembrane truncated and full length of the F gene of the RSV-B1 strain, respectively, were engineered. Comparative immunogenicity studies in BALB/c mice showed that each vector was capable of inducing RSV-B1-specific antibodies that cross-reacted with the RSV-long and RSV-A2 viruses. The anti-RSV-B1 antibodies were neutralizing, and exhibited strong cross-neutralizing activity against the RSV-long and RSV-A2 isolates as well. Analysis of the cellular responses revealed that animals immunized with rAd-F0ΔTM and rAd-F0 elicited CD4⁺ T-cell responses of the Th1 and Th2 phenotypes, as well as F protein-specific CTLs. Production of Th2 cytokines (IL-4, IL-5 and IL-13) by splenocytes of the rAd-F0ΔTM and rAd-F0 immunized mice was markedly lower than those released by animals administered with heat-inactivated RSV-B1 (HIRSV-B1). Comparison of the overall humoral and cellular responses suggests that rAd-F0ΔTM is significantly more immunogenic than rAd-F0. The anti-viral immunity generated by both recombinant adenovirus vectors has conferred protection against live RSV-B1 challenge as judged by the lower viral load recovered in the lungs, a faster rate of recovery of body weight loss, and a lower count of eosinophils as compared to eosinophilia in mice immunized with HIRSV-B1. Results from these studies suggest that rAd-F0ΔTM or rAd-F0 possess immunogenic properties that meet the requirements expected from potential RSV vaccine candidates.     

Corneal macrophage infiltrates following ocular herpes simplex virus type 1 challenge vary in BALB/c mice vaccinated with different vaccines

Macrophage cell infiltrates in the cornea were examined following ocular herpes simplex virus type 1 (HSV-1) challenge of vaccinated BALB/c mice. Mice were vaccinated with individual HSV-1 glycoproteins, cocktails of different HSV-1 glycoproteins, or live avirulent HSV-1 (strain KOS). Cryostat sections of cornea were taken at different times after challenge and reacted with M1/70, F4/80, BM8, or MOMA-1 monoclonal antibodies. The pattern of macrophage responses in the cornea differed depending on the vaccine that was given prior to HSV-1 ocular challenge. No macrophage response was detected in mice vaccinated with the highly protective 5gPs consisting of the five glycoproteins gB, gC, gD, gE, and gI. In contrast, mock vaccinated mice and mice vaccinated with gK, which is known to exacerbate HSV-1 induced eye disease, had high sustained macrophage responses. Mice vaccinated with 7gPs (5gPs+gG and gH) had moderate levels of macrophages. It appeared that (1) the most effective vaccines induced no detectable infiltrating macrophages in the eyes, while the least efficacious vaccines had very high levels of infiltrating macrophages; (2) presence of CD11b(+) cells in the cornea appeared to correlate with enhanced blepharitis, but did not appear to affect corneal scarring; and (3) presence of F4/80(+) cells in the cornea tended to correlate with increased corneal scarring.     

Vaccination of infant macaques with a recombinant modified vaccinia virus Ankara expressing the respiratory syncytial virus F and G genes does not predispose for immunopathology

We have evaluated the safety and immunogenicity of a recombinant modified vaccinia virus Ankara (MVA) vector expressing the respiratory syncytial virus (RSV) fusion (F) and attachment (G) proteins in infant macaques. Animals were vaccinated twice and 4 months later challenged with RSV. Although vaccination did not predispose for immunopathology upon challenge, we were also unable to demonstrate protection. Since vaccination had resulted in priming for secondary immune responses upon challenge, we suggest that vaccination efficacy will have to be improved by using MVA in a prime-boost strategy.     

Protective immunity to DENV2 after immunization with a recombinant NS1 protein using a genetically detoxified heat-labile toxin as an adjuvant

The dengue virus non-structural 1 (NS1) protein contributes to evasion of host immune defenses and represents a target for immune responses. Evidences generated in experimental models, as well as the immune responses elicited by infected individuals, showed that induction of anti-NS1 immunity correlates with protective immunity but may also result in the generation of cross-reactive antibodies that recognize platelets and proteins involved in the coagulation cascade. In the present work, we evaluated the immune responses, protection to type 2 dengue virus (DENV2) challenges and safety parameters in BALB/c mice vaccinated with a recombinant NS1 protein in combination with three different adjuvants: aluminum hydroxide (alum), Freund's adjuvant (FA) or a genetically detoxified derivative of the heat-labile toxin (LT_G33D), originally produced by some enterotoxigenic Escherichia coli (ETEC) strains. Mice were subcutaneously (s.c.) immunized with different vaccine formulations and the induced NS1-specific responses, including serum antibodies and T cell responses, were measured. Mice were also subjected to lethal challenges with the DENV2 NGC strain. The results showed that maximal protective immunity (50%) was achieved in mice vaccinated with NS1 in combination with LT_G33D. Analyses of the NS1-specific immune responses showed that the anti-virus protection correlated mainly with the serum anti-NS1 antibody responses including higher avidity to the target antigen. Mice immunized with LT_G33D elicited a prevailing IgG2a subclass response and generated antibodies with stronger affinity to the antigen than those generated in mice immunized with the other vaccine formulations. The vaccine formulations were also evaluated regarding induction of deleterious side effects and, in contrast to mice immunized with the FA-adjuvanted vaccine, no significant hepatic damage or enhanced C-reactive protein levels were detected in mice immunized with NS1 and LT_G33D. Similarly, no detectable alterations in bleeding time and hematological parameters were detected in mice vaccinated with NS1 and LT_G33D. Altogether, these results indicate that the combination of a purified recombinant NS1 and a nontoxic LT derivative is a promising alternative for the generation of safe and effective protein-based anti-dengue vaccine.     

Immunization and challenge experiments with a new modified live bovine herpesvirus type 1 marker vaccine prototype adjuvanted with a co-polymer

Western European control programs against bovine herpesvirus type 1 (BoHV-1) infections utilize attenuated BoHV-1 marker vaccines with a deletion of the glycoprotein E (gE) encoding gene. However, a recent study demonstrated the potential risk of virulence recovery of gE-deleted BoHV-1 marker vaccine strains due to recombination (Muylkens et al. [15]). Based on an infectious bacterial artificial chromosome clone, a gE- and thymidine kinase (TK)-gene-deleted BoHV-1 mutant (BoHV-1ΔgEΔTK) was constructed. The recombinant virus was subsequently tested as a novel modified live marker vaccine candidate in an immunization-challenge trial using BoHV-1 seronegative calves. Additionally, a non-virucidal co-polymer was tested together with the recombinant virus acting as a vaccine-adjuvant. Animals were vaccinated twice through intramuscular injection and challenged intranasally 3 weeks later with a virulent BoHV-1 field strain. Duration and titres of challenge virus shedding were significantly reduced in all vaccinees. Importantly, reduction of challenge virus shedding and serological antibody levels in response to vaccination with vaccine preparations containing the co-polymer-adjuvant were markedly improved when compared to vaccine formulations without an adjuvant. Taken together, our study describes a novel double deletion mutant as a safe and efficacious BoHV-1-prototype marker vaccine strain with enhanced protective capacity especially when administered together with a co-polymer adjuvant.     

No benefit of therapeutic vaccination in clinically healthy cats persistently infected with feline leukemia virus

Therapeutic vaccinations have a potential application in infections where no curative treatment is available. In contrast to HIV, efficacious vaccines for a cat retrovirus, feline leukemia virus (FeLV), are commercially available. However, the infection is still prevalent, and no effective treatment of the infection is known. By vaccinating persistently FeLV-infected cats and presenting FeLV antigens to the immune system of the host, e.g., in the form of recombinant and/or adjuvanted antigens, we intended to shift the balance toward an advantage of the host so that persistent infection could be overcome by the infected cat. Two commercially available FeLV vaccines efficacious in protecting naïve cats from FeLV infection were tested in six experimentally and persistently FeLV-infected cats: first, a canarypox-vectored vaccine, and second, an adjuvanted, recombinant envelope vaccine was repeatedly administered with the aim to stimulate the immune system. No beneficial effects on p27 antigen and plasma viral RNA loads, anti-FeLV antibodies, or life expectancy of the cats were detected. The cats were unable to overcome or decrease viremia. Some cats developed antibodies to FeLV antigens although not protective. Thus, we cannot recommend vaccinating persistently FeLV-infected cats as a means of improving their FeLV status, quality of life or life expectancy. We suggest testing of all cats for FeLV infection prior to FeLV vaccination.     

Efficacy of live adjuvanted mesogenic Newcastle disease vaccine in chickens.

120 white leghorn chickens primed with a lentogenic Newcastle disease (ND) live vaccine at 7 days of age were divided into three equal groups of 8 weeks of age and vaccinated with a live mesogenic ND vaccine (NDV). One group received only Newcastle disease mesogenic vaccine (RDVK) in normal saline, the second group received RDVK with groundnut oil as adjuvant and the third group received RDVK with liquid paraffin as adjuvant. Sera were collected at different time points for the assessment of antibody level against ND virus (NDV) by the haemagglutination inhibition (HI) test. The commonly used non-adjuvanted RDVK could not evince 100% protective HI titre beyond 11 weeks of age but in both the adjuvanted groups 100% protective HI titre was evident up to 20 weeks of age. On challenge at 20 weeks of age both the adjuvanted groups withstood challenge but in the non-adjuvanted group 80% of chickens withstood the challenge. A significant difference in immune response between the adjuvanted and non-adjuvanted groups was seen but not between both the adjuvanted groups. The advantage of vegetable oil (groundnut oil) as an adjuvant for live mesogenic ND vaccine has been discussed.     

A recombinant vesicular stomatitis virus replicon vaccine protects chickens from highly pathogenic avian influenza virus (H7N1)

Highly pathogenic avian influenza viruses (HPAIV) of subtypes H5 and H7 cause fatal disease in poultry (fowl plague) but also have zoonotic potential. Currently commercially available vaccines often do not provide sufficient protection and do not allow easy discrimination between vaccinated and infected birds. Therefore, vaccination of domestic poultry against H5 and H7 HPAIV is not allowed in many countries, or is only possible after special permission has been provided. We generated a recombinant marker vaccine based on non-transmissible vesicular stomatitis virus (VSV) expressing the HA antigen of HPAIV A/FPV/Rostock/34 (H7N1) in place of the VSV G gene. This virus, VSV*ΔG(HA), was propagated on a helper cell line providing VSV G in trans. Since no progeny virus was produced after infection of non-complementing cells, the vector was classified as biosafety level 1 organism (“safe”). Chickens were immunized via the intramuscular route. Following booster vaccination with the same replicons high titers of serum antibodies were induced, which neutralized avian influenza viruses of subtypes H7N1 and H7N7 but not H5N2. Vaccinated chickens were protected against a lethal dose of heterologous HPAIV A/chicken/Italy/445/99 (H7N1). Secretion of challenge virus was short-term and significantly reduced. Finally, it was possible to discriminate vaccinated chickens from infected ones by a simple ELISA assay. We propose that VSV replicons have the potential to be developed to high-quality vaccines for protection of poultry against different subtypes of avian influenza viruses.