Specific binding of the autoantigenic BCR targets to the surface of the respective CLL cells. Staining of patient 45’s CLL cells using the specific (autologous) antigen SMCHD1 and an antigen (PC9) targeted by another patient’s CLL-BCR. R1, viable cells; R2, dead cells. (A) Unstained cells; (B) staining with CD5-FITC/CD19-PE; (C) staining with specific antigen SMCHD1 (antigen-presenting cell [APC] channel); (D) staining with unspecific antigen PC9 (APC channel); (E) overlay of the histograms shown in panels A-D. The green line represents the specific antigen as shown in panel C.