AID is constitutively expressed in some WM samples. Single-stage RT-PCR showed positive bands in 2 WM BM samples (A). Various splice variants (SVs) identified in WM are summarized in panel B. Single-cell analysis of WM1-01 CD20⁺ cells (C) and activated CD20⁺ cells of healthy controls (D) were analyzed for clonotypic CDR2/CDR3 and AID expression.