Cytokine-dependent ex vivo expansion of early subsets of CD34+ cord blood myeloid progenitors is enhanced by cord blood plasma, but expansion of the more mature subsets of progenitors is favored.

Expansion of stem/progenitor cells has important implications for transplantation. We recently reported that a factor or factors in cord blood (CB), but not adult peripheral blood (PB), plasma enhanced replating of granulocyte erythroid macrophage megakaryocyte colony-forming units (CFU-GEMM) progenitors, a measure of self-renewal capacity. In this context, we evaluated effects of CB plasma, in comparison with PB plasma and fetal bovine serum (FBS), on ex vivo expansion of CD34+ column-separated (72-98% CD34+) CB cells using stroma-free cultures in the absence and presence of either PIXY321 (a granulocyte-macrophage colony-stimulating factor/interleukin-3 [GM-CSF/IL-3] fusion protein), IL-3+IL-6+IL-1, or steel factor (SLF) -/+ PIXY. CB plasma, PB plasma, or FBS alone did not sustain cell numbers. Combinations of CB plasma +SLF+PIXY induced maximal cumulative nucleated cell expansion (1044-fold), which was greater than that of PB plasma plus cytokines (633-fold) and FBS plus cytokines (142-fold). Total CD34+ cells peaked by day 7 with 7-fold expansion in the presence of CB plasma+SLF+PIXY compared with PB plasma or FBS with these same cytokines (threefold each). By day 7, total CFU-GEMM production in the presence of either PIXY, SLF+PIXY, or IL-3+IL-6+IL-1 was greater with CB plasma (maximum 11.4-fold average increases) than with PB plasma (6.8-fold increase). These increases were greater than with FBS. However, PB plasma was at least as good as CB plasma for expansion of immature and mature subsets of CFU-GM. The frequency of progenitors decreased with time, and expansion was coupled with differentiation. Although the proliferative capacity of CFU-GEMM was maintained, the capacity of CFU-GEMM to be replated decreased after time in suspension culture, suggesting age-related commitment of cells. Moreover, with plasma +SLF+PIXY for 7 days, expansion of more mature CFU-GM (responsive to GM-CSF) was greater (16-146-fold with CB plasma and 31-208-fold with PB plasma) than immature CFU-GM (responsive to GM-CSF+SFL) (4- to 14-fold with CB plasma and 6- to 17-fold with PB plasma). The results suggest that CB plasma enhances expansion of CFU-GEMM to a greater extent than PB plasma or FBS, but expansion in these cultures favors more mature subsets of cells.