Individual and combined effects of mesenchymal stromal cells and recombinant stimulatory cytokines on the in vitro growth of primitive hematopoietic cells from human umbilical cord blood

Background aims We have previously characterized the in vitro growth of two cord blood-derived hematopoietic cell populations in liquid cultures supplemented with recombinant cytokines. In the present study, we assessed the effects of bone marrow-derived mesenchymal stromal cells (MSC) on the growth of such cells. Methods CD34(+) CD38(+) Lin(-) and CD34(+) CD38(-) Lin(-) cells were obtained by negative selection, and cultured in the presence of marrow-derived MSC and/or early-and late-acting cytokines. Hematopoietic cell growth was assessed throughout a 30-day culture period. Results In the presence of MSC alone, both populations showed significant proliferation. Direct contact between MSC and CD34(+) cells was fundamental for optimal growth, especially for CD34(+) CD38(-) Lin(-) cells. In the presence of early-acting cytokines alone, cell growth was significantly higher than in cultures established with MSC but no cytokines. In cultures containing both MSC and early-acting cytokines, a further stimulation was observed only for CD34(+) CD38(-) Lin(-) cells. The cytokine cocktail containing both early-and late-acting cytokines was significantly more potent at inducing hematopoietic cell growth than the early-acting cytokine cocktail. When cultures were supplemented with early-and late-acting cytokines, MSC had no further effect on the growth of hematopoietic cells. Conclusions MSC seem to play a key role, particularly on more primitive (CD34(+) CD38(-) Lin(-)) cells, only in the absence of cytokines or the presence of early-acting cytokines. When both early-and late-acting cytokines are present in culture, MSC seem to be unnecessary for optimal development of CFC and CD34(+) cells.