Accessory cell function of CD40L-activated BCP-ALL cells in MLR. Leukemia cells were sorted immunomagnetically and were cocultured with CD40L-transfected J558 cell line for 48 hours. (top) Untreated BCP-ALL cells and CD40L-activated BCP-ALL cells were used as stimulators at 3%. Normal DCs were differentiated from monocytes in the presence of GM-CSF + IL-13 and were activated for 48 hours with CD40 ligand–transfected J558. (bottom) Untreated (□) and CD40L-activated (▪) BCP-ALL cells were used as stimulators at the indicated concentrations. Results of 3 representative experiments are shown. Proliferation of naive T cells (2 × 105/well) was assessed using [³H]-thymidine uptake during the last 18 hours of a 5-day experiment. Results show the mean ± SD of the ³H thymidine uptake of 3 replicates.