Using three different transgenic strains of mice representing an early-onset benign CD5+ B cell lymphocytosis (dnRAG1 mice), an established murine model of CLL (Eμ-TCL1 mice), and a model of accelerated murine CLL progression (DTG mice), we have confirmed the earlier observation that a subset of CD5+ B cells in Eμ-TCL1 mice (and WT mice) support inducible IL10 production after LPS + PIM treatment in vitro [8], and established here that splenic CD5+ B cells accumulating in dnRAG1 and DTG mice are also IL10 competent. The gene discussed is IL10; the disease is B-cell chronic lymphocytic leukemia.