Our “in vitro” transduction protocol of Tal-1−/− and Runx1−/− differentiating ESCs could also be used to detect differences in the activities of mutated forms of these genes that are found in acute leukemia, therapy-derived leukemia, myelodysplastic syndrome, and chronic myelomonocytic leukemia. The gene discussed is RUNX1; the disease is chronic myelomonocytic leukemia.