Expression levels of CD55 and CD59 on MM cells increase at the time of progression. (A) CD55, CD59, and CD46 expression levels on MM cells from BM samples obtained from 21 MM patients, who were subsequently treated with daratumumab at a dose of 16 mg/kg in the GEN501 study. BM samples were obtained before start of daratumumab, before the 10th daratumumab infusion, and at the time of progression (PD). Data are presented as mean ± SEM. P values between the indicated groups were calculated using a paired Student t test; *P < .05, **P < .01, ns, not significant. (B) CD55, CD59, and CD46 expression levels on circulating MM cells before start of daratumumab treatment, during daratumumab treatment, and at the time of progression (PD) (n = 11 patients). Expression levels of the complement-inhibitory proteins were analyzed by flow cytometry. Data are presented as mean ± SEM. P values between the indicated groups were calculated using a paired Student t test; *P < .05, **P < .01, ns, not significant.