Fig. 2

Daratumumab binds to CD34+ cells but C1q does not. Daratumumab does not induce complement-dependent cytotoxicity of CD34+ cells in vitro. a CD34+ cells and the control cells were incubated with daratumumab and its binding was confirmed for < 1% of IM-9, 99% of Daudi, 96% of KG-1, and 40% of CD34+ cells; the isotype control bound to 5% of the CD34+ cells. This is a representative flow plot with controls as designated. b After incubation with complement-rich human serum, C1q binding was assessed. C1q was found on Daudi but was negligible on the other cells (mean ± SD). c When the density of CD38 is sufficient, the binding of daratumumab is also adequate for formation of the membrane attack complex by C1q, permitting CDC to occur [16]. As this graph depicts, daratumumab-mediated CDC occurs with Daudi and minimally with KG-1 but not with CD34+ or IM-9 cells (mean ± SD, n = 3)