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 o f transplantable stem cells for a variety of clinical conditions. In t his study, we have attempted to further characterize the primitive pro genitors in CB. First we analyzed the effects of early-acting growth f actors on blast cell colony formation from CD34(+) progenitors. Additi on of Steel factor (SF), interleukin-6 (IL-6), or granulocyte colony-s timulating factor (G-CSF) to cultures containing interleukin-3 enhance d blast cell colony formation. These results indicated that cell cycle -dormant progenitors are present in CB. Next, based on results obtaine d in the murine system, we tested whether c-kit expression could separ ate the CB progenitors into cycle-dormant vs. cycle-active progenitors . Cells were separated into CD34(+) c-kit(-), c-kit(low), and c-kit(hi gh). 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 th e opposite is true for other colony-forming cells. Expression of c-kit may be useful in identifying CB progenitors with long-term engraftmen t capability.