Dependency of rituximab-induced complement-lysis. Efficacy increases with higher intensity of CD20 expression (A) and with inhibition of complement-regulatory antigens (B). In panel A, 18 samples (9 pairs) of BCP-ALL at diagnosis (○) and from follow-up (•) were analyzed for CD20 expression levels (MFI values) and blast cell recovery on in vitro rituximab/complement incubations. The (continuous) regression line and the MFI channel = 50 (dotted line) are shown. Note that all but one follow-up sample show higher CD20 expression than initial samples along with more efficacious rituximab-lysis (best separator apparently at MFI = 50). In panel B, comparisons of complement-lysis efficacy with rituximab alone vs rituximab plus additional mini-antibodies against CD55 and CD59, denoted “augmented” lysis, are shown. Twelve samples (from 6 of the 9 pairs, as earlier in this figure legend) were tested. Differences between incubations were minor but statistically significant.