MIP-1α and TGF-β production in CD34+ progenitor-stromal cell coculture systems: Effects of progenitor isolation method and cell-cell contact

Macrophage inflammatory protein-1α (MIP-1α) is a C-C chemokine which has antiproliferative effects on early hematopoietic progenitors and stimulatory effects on later progenitors. It also possesses chemotactic and activating properties for monocytes, macrophages, and T-cells. CD34+ progenitors isolated utilizing an avidin-biotin immunoadsorption column produced significant amounts of MIP-1α from 24 h onward when cultured in medium with 10% fetal calf serum (>200 pg/ml). Such production persisted through 96 h of culture and was greater when such progenitors were cocultured with a preformed marrow stromal layer (4000 pg/ml at 24 h). The production of MIP-1α declined over time of coculture with stromal layers, and stromal layers themselves produced minimal MIP-1α as detected by ELISA: <100 pg/ml. In contrast, CD34+ cells isolated by flow cytometry or by magnetic bead adsorption produced minimal MIP-1α (0-30 pg/ml). MIP-1α production also increased when cells isolated by these two methods were cocultured with stromal layers. The difference in MIP-1α production could not be accounted for by differences in purity of the CD34+ population between isolation methods nor on the basis of monocytic or lymphocytic contamination as assessed by the presence of CD14 or CD3 positive cells. CD34+ cells isolated by immune adsorption had increased expression of endothelial and mesenchymal associated antigens, however, suggesting that this subpopulation might account for the MIP-1α production observed. Freshly isolated CD34+ cells expressed MIP-1α message as assessed by RT-PCR and by in situ hybridization. Coculture of CD34+ cells isolated by any means with stromal cells increased transforming growth factor-β (TGF-β) production, in this case by the stromal layer itself. Both MIP-1α and TGF-β have been found to influence cell cycle status and proliferation status of early hematopoietic progenitors, and both have potential effects on accessory cell function. These studies indicate that progenitor-stromal cell interactions may influence local cytokine output, thus potentially influencing progenitor cycling status and accessory cell activation. The method of isolation of CD34+ progenitors may influence secretion of certain cytokines and chemokines. (C) 2000 Academic Press.