Characterization of c-kit expression by primitive hematopoietic progenitors in umbilical cord blood

Human umbilical cord blood (CB) appears to be an exciting new source of transplantable stem cells for a variety of clinical conditions. In this study, we have attempted to further characterize the primitive progenitors in CB. First we analyzed the effects of early-acting growth factors on blast cell colony formation from CD34(+) progenitors. Addition of Steel factor (SF), interleukin-6 (IL-6), or granulocyte colony-stimulating factor (G-CSF) to cultures containing interleukin-3 enhanced blast cell colony formation. These results indicated that cell cycle-dormant progenitors are present in CB. Next, based on results obtained in the murine system, we tested whether c-kit expression could separate the CB progenitors into cycle-dormant vs. cycle-active progenitors. Cells were separated into CD34(+) c-kit(-), c-kit(low), and c-kit(high). The results suggested that the c-kit(low) population contains the majority of cycle-dormant progenitors and the C-kit(high) population contains most of the actively cycling cells. The majority of the blast cell colony forming cells were in the c-kit(low) population, while the opposite is true for other colony-forming cells. Expression of c-kit may be useful in identifying CB progenitors with long-term engraftment capability.