Functional virus-specific CTL responses. Effector rabbit PBMCs were used in triplicate, either freshly prepared or following Ag-stimulation and expansion with IL-2. SV40-immortalised autologous target rabbit fibroblasts were labelled with [51Cr], and the cytotoxicity determined after the last immunisation. Non-stimulated and FPenv-stimulated target fibroblasts were used as negative and irrelevant controls. Cytolytic E6- and E7-specific T-cell activity were induced in most of the rabbits (Protocols 1 and 2; [E:T] ratio 30:1). Rabbit # 81 of Protocol 3/E7 was unresponsive to pE7. The results are shown as means of three to four assays.