CD5 and B-cell chronic lymphocytic leukemia: To answer this question, we performed functional studies determining the expression level of p27Kip1 and cyclin D2 proteins in both leukemic (CD19+CD5+) cells and non-malignant T cells, as well as the rate of apoptosis in CD19+ and CD3+ cells from the peripheral blood of CLL patients divided based on genotype at all polymorphic sites of the CDKN1B and CCND2 genes examined.