CTL activity of CD8⁺ T cells from week 2 vaccinated mice is higher than CTL activity from week 1 vaccinated mice. SJL/J mice were injected with 10⁵ AML cells. One or 2 weeks later they were immunized with irradiated 10⁵ B7-AML cells. One week after immunization CD8⁺ splenocytes were isolated as described in Materials and Methods and used as effector cells in various effector to target (E:T) ratios. Target cells (autologous AML or control EL-4 cells) were incubated with ⁵¹Cr for 2 hours. The standard 4-hour CTL assays were set up with various E:T ratios in a total volume of 0.2 mL/well in a 96-well microtiter plate. All conditions were set up in quadruplicate. After a 4-hour incubation, 100 μL of supernatant was harvested from each well, and the quantity of ⁵¹Cr in the supernatants was determined. (A) CTL activity of CD8⁺ cells from week 1 vaccinated mice on autologous AML cells (Vac/AML) and control EL-4 cells (Vac/EL-4). In the same experiment, CD8⁺ cells from normal SJL/J mice were tested for CTL activity on autologous AML cells (Norm/AML) and control EL-4 cells (Norm/EL-4). (B) CTL activity of CD8⁺ cells from week 2 vaccinated mice on autologous AML cells (Vac/AML) and control EL-4 cells (Vac/EL-4). Control cells from normal SJL/J mice were used as described in graph A.