CD40L/OX40L-stimulated T cells have cytotoxic activity against autologous leukemia cells in a CFSE-based flow cytometry assay. (A) The x-axis represents CFSE-labeled B-CLL cells, gated on viable cells, and the y-axis represents the CD3 PerCP-positive population. Numbers represent the events counted in each gate (R3 for B-CLL cells and R4 for CTLs). (left panel) Time 0. (right panel) 18-hour analysis. (i) CFSE-labeled B-CLL cells cocultured with autologous CD40L/OX40L-stimulated T cells. The B-CLL cells are reduced by 71%. (ii) CTLs cocultured with mismatched allogeneic B-CLL cells. B-CLL cells are reduced by 9.3%. (iii) Autologous CFSE-labeled B-CLL cells alone. B-CLL cells are reduced by 3%. (B) Reduction in B-CLL cell numbers (mean + SD; 4 donors tested) with and without MHC class 1 and 2 blocking. Difference was statistically significant (P < .05 for MHC class 1 and class 2 blocking).