MATURE ACCESSORY CELLS INFLUENCE LONG-TERM GROWTH OF HUMAN HEMATOPOIETIC PROGENITORS ON A MURINE STROMAL CELL FEEDER LAYER

A recently described long-term culture system for early human progenit or cells was established with the murine preadipocyte stromal line FBM D-1 grown in 96-well plates; cobblestone areas formed by inoculated he matopoietic cells are determined in a limiting dilution setting after five weeks' culture. To compare the capacity of cobblestone-area-formi ng cell (CAFC) formation by bone marrow and leukapheresis products in this system, mononuclear cells (MNC) of both origins were cultured. As related to CD34(+) cell content, CAFC yields after five weeks' cultur e were in the same range in bone marrow and leukapheresis stemming fro m patients with efficient mobilization of hematopoietic cells. In puri fied CD34(+) cell fractions, the CAFC yield per inoculated cell number was considerably higher than in MNC; however, if the CAFC number was related to the inoculated CD34(+) cell number in MNC and after purific ation, the yield was four to eight times decreased in purified fractio ns. Addition of the mature cells brought the CAFC yield back up to the numbers obtained in the unseparated MNC fraction. By contrast, slight ly more advanced progenitors per CAFC were found in cultures of purifi ed hematopoietic cells from both origins than in whole MNC. The result s suggest that mature human accessory cells give noticeable support to recruitment of early progenitors on this feeder but lead to lower yie ld of GM progenitors.