Recombinant retroviral vectors that express the Env and Rev proteins of feline immunodeficiency virus (FIV) were prepared and analyzed in a mouse model system for their ability to induce antigen-specific CD8 + CTL (cytotoxic T lymphocyte) responses. The ultimate goal of these studies is to develop effective immunogens for CTL induction in the cat. Recombinant Env/Rev retroviral vectors were used to transduce mouse fibroblasts and these cells were then inoculated intraperitoneally into syngeneic BALB/c mice. FIV Env-specific CTL responses were obtained. The potent ability of recombinant retroviral vector-transduced cells to elicit cell-mediated immunity in the mouse model offers the possibility that such delivery systems may serve as therapeutic and/or prophylactic treatments against FIV infection in the cat.