Expression of CD52 and CD20 in primary ALL and detection of GPI-defective cells. Twenty-four ALL samples taken at diagnosis were analyzed by flow cytometry. (A) Expression of CD52 according to subtype. The dotted line represents the fluorescence intensity of isotype controls. (B) Expression of CD20 according to subtype. (C) Top: Expression of CD52 and CD20 within double-positive cases (patients 11, 15, 23, and 24). In 11 of 19 cases in which the bulk of the cells expressed CD52, distinct CD52⁻ subpopulations were detected. Middle: CD52⁻ cells express CD10, indicating their leukemic origin. Bottom: CD52⁻ cells show concurrent loss of CD55, indicating a GPI-defective phenotype.