(A) Inhibition of fludarabine-induced apoptosis by the anti-CD40 MoAb G28-5. (B) Samples with no response or only low response to anti-CD40 MoAb. Cells (1 × 10⁶/mL) from patients with B-CLL were incubated in 10% FCS-RPMI 1640 medium with fludarabine (0.8 μg/mL) and in the absence or presence of MoAb G28-5 (ascites, 1:1000). After 3 days of cell culture the percentages of apoptosis were calculated. Any experimental point has been performed in duplicate; standard deviations of the mean apoptosis values were less than 10%. The levels of apoptosis in cells incubated without fludarabine, either in the presence or the absence of anti-CD40 MoAb, were less than 10%.