CD55 and CD59 block rituximab and complement-mediated lysis.

PBMCs from 33 patients with B-CLL and 5 patients with PLL were lysed with rituximab and 25% human serum in the presence or absence of blocking anti-CD55 and/or anti-CD59 antibodies (10 μg/mL). Lysis was measured after 4 hours with the Alamar blue assay. (A) The mean and SDs obtained with 6 different representative patients are shown. (B) The mean lysis and SDs for all 38 patients are shown. (C) The mean lysis of the 30 low responders (basal lysis less than 25%; black bars) and of the 8 high responders (basal lysis greater than 30%; hatched bars) and SDs are shown.