CD40L L cells stimulate the proliferation of DOX-treated lymphoma cells. Cells were incubated with DOX 0 μg/mL (1), 0.1 μg/mL (2) and (3), 0.5 μg/mL (4) and (5), 1 μg/mL (6) and (7) for 24 hours (0.5 or 1 μg/mL) or 30 hours (0.1 μg/mL) and with (3), (5), and (7) or without (1), (2), (4), and (6) irradiated CD40L L cells, then washed and cultured without DOX, but otherwise in the same conditions during 48 additional hours before measurement of [³H]TdR incorporation. [³H]TdR incorporation of all five lymphoma cell lines treated with DOX 0.1 μg/mL (2 v 3), 0.5 μg/mL (4 v 5) was significantly (Student’s t-test, P < .05) increased on coculture with irradiated CD40L L cells as compared with no L cells or L cells expressing CDw32 (not shown); with 1 μg/mL of DOX (6 v 7), the increase was significant only for the Daudi and BL70 cell lines. These results are the mean and SD of five different experiments.