Effect of anti-CD28 on CTL apoptosis during T-cell targeting. T cells were generated by activation of peripheral blood T cells by CD3 cross-linking and culture for 7 days in IL-2–supplemented medium (30 U/ml). T cells were then cultured for 24 hours at an E/T ratio of 10:1 in the absence or presence of CD3x19 bs ab (10 μg/mL). Control cultures were performed with medium alone (ie, only T cells plus [a] Nalm-6 or [b] Raji), monospecific control antibodies plus tumor cells (OKT3 and HD37 at 5 μg/mL), anti-CD28 (15E8, 1 μg/mL), IgM-control mab (G155-228, 10 μg/ml), or anti-B7.1 (BB-1, 10 μg/ml). After incubation, the remaining B lymphoma cells were removed from the coculture by immunomagnetic depletion with anti-CD19 and anti-CD20 as described.10 T-cell apoptosis was measured on the single cell level as described.15