B7-1 IgG costimulates allogeneic T cells after binding to the tumor membrane.
Resting (A) or PHA-preactivated (B) T cells isolated from a healthy donor (5 × 104 per well) were cocultured with U937 cells (1 × 105 per well), which were inactivated with mitomycin C and preincubated with CD8 IgG (■) or B7-1 IgG (▪) (5 to 7 μg/106 cells) in 96-well plates coated with OKT3.3H-thymidine-uptake was measured after 48 to 72 hours of culture as described in “Materials and methods.” Data are expressed as mean ± SD of triplicate wells. T cells (resting/preactivated) alone: 0.3 ± 0.02 cpm × 103/2.9 ± 0.8 cpm × 103. U937 cells (CD8 IgG/B7-1 IgG) alone: 5.5 ± 2.2 cpm × 103/3.9 ± 0.8 cpm × 103. Asterisks indicate P = .05 values by one-sided Wilcoxon tests for unpaired rank sums as compared with CD8 IgG-induced proliferation.
