APAF1 and leukemia: This expression profile would appropriately explain the in vitro acquired chemoresistant phenotype of CD34+ cells from high mobilizers: in fact, up regulation of BIRC genes was already reported to be related to drug resistance in leukemias and other cancers, as well as the down regulation of proapoptotic APAF1, FAS, FASL, TNFRSF25 [30-34].