Induction of feline immunodeficiency virus-specific cell-mediated and humoral immune responses following immunization with a multiple antigenic peptide from the envelope V3 domain

Cytotoxic T-cell determinants should be an important component of a vaccine against feline immunodeficiency virus (FIV). Epitope mapping studies have revealed an immunodominant neutralization epitope within the third variable (V3) domain of the viral envelope glycoprotein comprizing 17 amino acids (residues 390-406: RAISSWKQRNRWEWRPD). We have investigated the induction of FIV-specific cytotoxicity and anti-peptide antibody in cats immunized with a multiple antigenic peptide (MAP) containing this epitope. Virus-specific lymphocytotoxicity was determined using autologous or allogeneic skin fibroblasts as target cells labelled with chromium-51 and pulsed with overlapping 10 amino acid peptides. Cytotoxic effector cells derived from fresh peripheral blood were detected in five out of 10 immunized cats. The cell-mediated immune response appeared to be directed to envelope peptide 1 (RAISSWKQRN) and peptide 2 (SWKQRNRWEW), with recognition of peptide 3 (QRNRWEWRPD) in only one cat. An antibody response to the 17 amino acid peptide immunogen was detected in seven immunized cats, which was directed to envelope peptides 2 and 3. These results suggest that different epitopes may be recognized by the cell-mediated and humoral immune responses. None of the cats was protected from challenge with the Glasgow8 isolate of FIV (FIV/GL-8). This study has implications for vaccine strategies using synthetic peptides to induce virus-specific cell-mediated immune responses