CD52⁻ GPI-defective ALL cells are highly susceptible to RTX-mediated CDC. CD52⁻ cells recovered from ALM-treated animals and CD52⁺ cells recovered from control animals were analyzed for expression of CD20 and susceptibility to RTX-CDC. Results from patient 15 are shown. (A) CD20 expression on CD52⁺ and CD52⁻ patient 15 cells was analyzed by staining of the cells with various concentrations of RTX-FITC, confirming that CD52⁺ and CD52⁻ cells expressed CD20 to similar levels. (B) Survival of CD52⁺ and CD52⁻ cells after 1 hour of exposure to various amounts of complement in the absence or presence of 10 μg/mL RTX. Decreased survival of CD52⁻ cells compared with CD52⁺ cells indicates increased susceptibility to RTX-CDC. (C) Survival of CD52⁻ cells and CD52⁺ cells after exposure to various concentrations of RTX in the absence or presence of 0.5% complement (COMP).