CD34 and leukemia: While the mechanism of Bcl-2 expression in CSC chemo/drug resistance is still unclear, and it might be due to chromosomal translocation or another pathway, it was demonstrated that leukaemia CD34+ cells expressed Bcl-2 and Bcl-X [48], and Bcl-2 was highly expressed in breast CD44+/CD24−/low CSCs [49].