STROMA-CONTACT PREVENTS LOSS OF HEMATOPOIETIC STEM-CELL QUALITY DURING EX-VIVO EXPANSION OF CD34(-BLOOD STEM-CELLS() MOBILIZED PERIPHERAL)

Stroma-supported long-term cultures (LTC) allow estimation of stem cel l quality by simultaneous enumeration of hematopoietic stem cell (HSC) frequencies in a graft using the cobblestone area forming cell (CAFC) assay, and the ability of the graft to generate progenitors in flask LTC (LTC-CFC). We have recently observed that the number and quality o f mobilized peripheral blood stem cells (PBSC) was low in patients hav ing received multiple rounds of chemotherapy. Moreover, grafts with lo w numbers of HSC and poor HSC quality had a high probability to cause graft failure upon their autologous infusion. Because ex vivo culture of stem cells has been suggested to present an attractive tool to impr ove hematological recovery or reduce graft size, we have studied the p ossibility that such propagation may affect stem cell quality. In orde r to do so, we have assessed the recovery of different stem cell subse ts in CD34(+) PBSC after a 7-day serum-free liquid culture using CAFC and LTC-CFC assays. A numerical expansion of stem cell subsets was obs erved in the presence of interleukin-3 (IL-3), stem cell factor, and I L-6, while stroma-contact, stromal soluble factors, or combined additi on of FLT3-ligand and thrombopoietin improved this parameter. In contr ast, ex vivo culture severely reduced the ability of the graft to prod uce progenitors in LTC while stromal soluble factors partly abrogated this quality toss. The best conservation of graft quality was observed when the PBSC were cultured in stroma-contact. These data suggest tha t ex vivo propagation of PBSC may allow numerical expansion of various stem cell subsets, however, at the expense of their quality. In addit ion, cytokine-driven PBSC cultures require stroma for optimal maintena nce of graft quality. (C) 1998 by The American Society of Hematology.