In a subsequent publication (3), we initially suggested that CD5+ B cell clonal populations present in old mice might be considered analogous to precursors of Chronic Lymphocytic Leukemia (CLL), the most frequent B cell neoplasm in the elderly (6), which is characterized by clonal expansion of CD5+ B cells and for which no pre-leukemic phase was defined. This evidence concerns the gene CD5 and B-cell chronic lymphocytic leukemia.