The addition of CXCR4/CD5 subpopulations (CXCR4DimCD5Dim, DDF; and CXCR4BrightCD5Bright, DBF) to the previously studied subpopulations (CXCR4DimCD5Bright, PF; CXCR4IntCD5Int, IF; and CXCR4BrightCD5Dim, RF) confirms that the PF and RF contain the youngest and oldest cells in CLL clones [1,2]. The gene discussed is CD5; the disease is B-cell chronic lymphocytic leukemia.