While examining the immune populations by flow cytometry, AID−/−/Eμ-TCL1 CLL cells were observed to have lower levels of B220, the CD45R isoform of the CD45 phosphatase, on the surface of CLL cells both in the peripheral blood and spleens of AID−/−/Eμ-TCL1 mice (Fig. 2A–C). This evidence concerns the gene AICDA and B-cell chronic lymphocytic leukemia.