CD38 ligation in the presence of IL-2 prolongs B-CLL survival but does not alter the apoptosis rate. (A) PI staining of B-CLL cells purified from 8 different patients (nos. 3, 8, 12, 14, 19, 20, 27, and 33) and cultured for 48 hours in the presence of the indicated treatment. IL-2 is the only agent able to confer mild protection from apoptosis, whereas the anti-CD38 mAb is ineffective. IgM was included as control and strongly promoted apoptosis. (B) Purified B-CLL cells from 8 patients (nos. 3, 8, 12, 14, 19, 20, 27, and 33) were cultured in presence of IL-2, the agonistic anti-CD38 mAb, or a combination of the two and evaluated weekly to monitor cell survival by the trypan blue exclusion test. Exposure to anti-CD38 mAb and IL-2 resulted in a substantial improvement in cell viability, already visible after 1 week and lasting for over 4 weeks.