CLL-like cells and maturing B cells (CD19+/CD5−) were further dissected according to CD21 and IgM expression to identify CD21+/IgM+ marginal zone/marginal zone progenitor (MZ/MZP) B cells, CD21int/IgMdim follicular B cells, and CD21−/IgM− or CD21−/IgM+ atypical B cells. This evidence concerns the gene CD19 and B-cell chronic lymphocytic leukemia.