AbstractSuccessful vaccination against West Nile virus (WNV) requires induction of both neutralizing antibodies and cell-mediated immune responses. In this study, we have assessed the ability of a recombinant ALVAC®-WNV vaccine (RECOMBITEK® WNV) to elicit neutralizing antibodies and virus-specific cell-mediated immune responses in horses. In addition, we examined whether prior exposure to ALVAC®-WNV vaccine would inhibit B and cell-mediated immune responses against the transgene product upon subsequent booster immunizations with the same vaccine. The results demonstrated that the recombinant ALVAC®-WNV vaccine induced neutralizing antibodies and prM/E insert-specific IFN-γ+ producing cells against WNV in vaccinated horses. Prior exposure to ALVAC®-WNV vaccine did not impair the ability of horses to respond to two subsequent booster injections with the same vaccine, although anti-vector-specific antibody and cell-mediated immune responses were induced in vaccinated horses. This report describes, for the first time, the induction of antigen-specific cell-mediated responses following vaccination with an ALVAC® virus recombinant vaccine encoding WNV antigens. Moreover, we showed that both WNV-specific IFN-γ producing cells and anti-WNV neutralizing antibody responses, are not inhibited by subsequent vaccinations with the same vector vaccine.
AbstractA recombinant canarypox virus vectored vaccine co-expressing synthetic genes encoding outer capsid proteins, VP2 and VP5, of African horse sickness virus (AHSV) serotype 4 (ALVAC®–AHSV4) has been demonstrated to fully protect horses against homologous challenge with virulent field virus. Guthrie et al. (2009) detected weak and variable titres of neutralizing antibody (ranging from <10 to 40) 8 weeks after vaccination leading us to hypothesize that there could be a participation of cell mediated immunity (CMI) in protection against AHSV4. The present study aimed at characterizing the CMI induced by the experimental ALVAC®–AHSV4 vaccine. Six horses received two vaccinations twenty-eight days apart and three horses remained unvaccinated. The detection of VP2/VP5 specific IFN-γ responses was assessed by enzyme linked immune spot (ELISpot) assay and clearly demonstrated that all ALVAC®–AHSV4 vaccinated horses developed significant IFN-γ production compared to unvaccinated horses. More detailed immune responses obtained by flow cytometry demonstrated that ALVAC®–AHSV4 vaccinations induced immune cells, mainly CD8+ T cells, able to recognize multiple T-epitopes through all VP2 and only the N-terminus sequence of VP5. Neither VP2 nor VP5 specific IFN-γ responses were detected in unvaccinated horses. Overall, our data demonstrated that an experimental recombinant canarypox based vaccine induced significant CMI specific for both VP2 and VP5 proteins of AHSV4.