ATMKO.CD3εKO B-cell tumors activate in vitro T-cell responses and undergo in vivo T cell–dependent rejection. (A) ATMKO.CD3εKO B-cell tumors grow progressively in T cell–deficient (CD3εKO) (closed symbols), but not in T cell–sufficient (B6 × 129)F1 (F1; open symbols, which are all on the x-axis), host mice. A total of 2 × 10⁶ B-cell lymphomas (B1, B2, and B3) were injected in 100 μL of phosphate-buffered saline into the anteromedial thigh of host mice, and tumor growth (plotted as tumor volume) was calculated as described in supplemental Materials and Methods. This experiment is representative of 4 independent experiments using 3 B-cell tumors and 2 to 4 host mice per group. (B) ATMKO.CD3εKO B-cell lymphomas stimulate in vitro CD4⁺ T-cell proliferation. No T cells (-) or a total of 1 × 10⁵ CD4⁺ T cells from (B6 × 129)F1 (F1) or BALB/c mice were cocultured with 1 × 10⁵ irradiated (60 Gy) B-cell lymphomas (none, B1, or B2) for 72 hours in 96-well plates. T-cell proliferation was assessed by [³H] thymidine uptake and presented as counts per minute (CPM) ± standard error of the mean for triplicate wells. This experiment is representative of 3 experiments using 2 B-cell tumors.