CD117 Also known as c-Kit, Steel factor receptor, and stem cell factor receptor, this tyrosine kinase protein is expressed primarily in hematopoietic progenitor cells, mast cells, and acute myeloid leukemia (AML) cells.CD117 activation promotes the proliferation and differentiation of these cell subsets. Lack of or defective stem cell factor can lead to reduced hematopoietic progenitor cell numbers and severe anemia.CD117 is also expressed by melanocytes and plays a role in signaling and activation of these cells.