HIV-1 p24 vaccine protects cats against feline immunodeficiency virus infection.

Background: Based on previous analysis of feline immunodeficiency virus (FIV)-specific cross-reactive antibodies to HIV-1 p24, cats vaccinated with HIV-1 p24 were evaluated for cross-reactive immunity to FIV. Objective: To determine the level of cross-reactivity that exists between HIV-1 and FIV p24 and its implications for vaccine prophylaxis. Methods: Specific-pathogen-free cats were immunized three times with HIV-1 p24 in Ribi adjuvant, with (n = 18) or without cytokine (n = 6). Control cats were immunized three times with adjuvant (n=10) or phosphate-buffered saline (PBS; n = 5). All immunized cats were challenged with either subtypes B or A/B FIV, and monitored by virus isolation, proviral PCR, FIV-specific antibodies, and feline interferon-γ ELISpot for T-cell activities. Results: Of 18 cats vaccinated with subtype B HIV-1 (HIV-1 LAI/LAA , HIV-1 UCD1 ) p24 in Ribi/cytokine adjuvant 14 (78%) were protected against FIV challenges (subtype A gag and B gag ) that infected all 15 adjuvant- or PBS-immunized cats. Furthermore, only three of six (50%) cats vaccinated with FIV p24 in Ribi/cytokine adjuvant were protected against similar FIV challenge. HIV-1 p24 vaccination induced weak cross-reactive antibodies to FIV p24, which did not correlate with vaccine efficacy. However, the peripheral blood mononuclear cells from HIV-1 p24-vaccinated/protected cats at 33-34 weeks post-FIV challenge responded to three T-cell responsive peptides at the carboxyl-terminus of the FIV p24, whereas those cells from the infected control cats had minimal to no responses to the same peptides. Conclusions: These results suggest the importance of including lentiviral p24 as vaccine immunogen for human AIDS vaccine. Moreover, these results suggest the potential importance of evolutionarily conserved, cross-protective epitopes in vaccine protection.