CYTOKINE-DEPENDENT EX-VIVO EXPANSION OF EARLY SUBSETS OF CD34(-BLOOD MYELOID PROGENITORS IS ENHANCED BY CORD-BLOOD PLASMA, BUT EXPANSION OFTHE MORE MATURE SUBSETS OF PROGENITORS IS FAVORED() CORD)

Expansion of stem/progenitor cells has important implications for tran splantation. We recently reported that a factor or factors in cord blo od (GIB), but not adult peripheral blood (PB), plasma enhanced replati ng of granulocyte erythroid macrophage megakaryocyte colony-forming un its (CFU-GEMM) progenitors, a measure of self-renewal capacity. In thi s context, we evaluated effects of CB plasma, in comparison with PB pl asma and fetal bovine serum (FBS), on ex vivo expansion of CD34(+) col umn-separated (72-98% CD34(+)) CB cells using stroma-free cultures in the absence and presence of either PIXY321 (a granulocyte-macrophage c olony-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-fol d), 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+P IXY, or IL-3+IL-6+IL-1 was greater with CB plasma (maximum 11.4-fold a verage increases) than with PB plasma (6.8-fold increase). These incre ases were greater than with FBS. However, PB plasma was at least as go od 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 C FU-GEMM was maintained, the capcity of CFU-GEMM to be replated decreas ed after time in suspension culture, suggesting age-related commitment of cells. Moreover, with plasma +SLF+PIXY for 7 days, expansion of mo re 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 (respon sive to GM-CSF+SFL) (4- to 14-fold with CB plasma and 6- to 17-fold wi th PB plasma). The results suggest that CB plasma enhances expansion o f CFU-GEMM to a greater extent than PB plasma or FBS, but expansion in these cultures favors more mature subsets of cells.