Induction of MYC and Ki67 protein expression as well as proliferation of leukemic CLL cells by binding of their autoantigenic BCR target. Shown is the analysis of PBMC from CLL patients (containing 82% CD5⁺/CD19⁺ cells) and purified (>95%) CD5⁺/CD19⁺ CLL cells derived from patient 45 after binding of the autoantigenic CLL-BCR target SMCHD1, the irrelevant CLL-BCR target MAZ, and αIgM. (A) Induction of MYC protein expression. 1, without antigen; 2, cells + αIgM; 3, cells + irrelevant antigen MAZ; 4, cells + specific antigen SMCHD1. (B) Flow cytometric analysis: Ki67 staining of purified CD5⁺/CD19⁺ cells. 1, unstained cells; 2: cells without antigen; 3, cells + αIgM; 4, cells with irrelevant antigen MAZ; 5, cells with specific antigen SMCHD1. (C) Proliferation of CLL cells as measured by EZ4U assay. PBMCs from CLL patient (left); purified CD5⁺/CD19⁺ CLL cells (right). The 4 columns represent, from left to right, no antigen, αIgM, unspecific antigen MAZ, and specific antigen SMCHD1.