Combination therapy leads to long-lasting tumor-specific CTL activity.

Splenocytes from mice that had been cured from EL-4 lymphoma (chemotherapy plus B7.2-IgG or chemotherapy plus B7.1- plus B7.2-IgG) were stimulated in vitro with irradiated EL-4 cells as described in “Materials and methods.” At 6 days later, cells were harvested and used as effector cells in the indicated E/T ratios. Target cells (H-2^b EL-4 or control H-2^s AML cells) were incubated with ⁵¹Cr for 90 minutes. The standard 4-hour CTL assays were set up in a total volume of 0.2 mL per well in 96-well microtiter plate. All conditions were set up in quadruplicate. As control in the experiment, normal C57BL/6 splenocytes were tested for CTL activity on EL-4 and AML cells. Splenocytes from combination-treated mice had strong CTL activity against EL-4 cells but not AML cells.