In order to determine the role of EC in CML proliferation and retention of the stem cell immunophenotype, the CML bulk (CD45+) and stem cell (CD34+CD38-) populations were tracked at 24, 48 and 72 h by multi-staining with CFSE, and primitive immunophenotype markers after 3 days of co-culture in the presence of EC. This evidence concerns the gene PTPRC and chronic myelogenous leukemia, BCR-ABL1 positive.