The role of recombinant haematopoietic growth factors in human long-term bone marrow culture in serum-free medium.

We have previously reported prolonged in vitro maintenance of human bone marrow progenitor cells using a serum-free (SF) liquid culture system. The present study was undertaken to determine recombinant growth factor (rGF) requirement of long-term marrow culture (LTMC) in absence of exogenous serum, to avoid interference of any undefined components. Our data clearly show that the presence of serum is a major obstacle to the correct evaluation of rGF activity. However, in SF conditions the sequential analysis of these rGFs, alone or in combination, clearly showed a stimulating activity of interleukin 3 (IL3), granulocyte-macrophage colony-stimulating factor (GM-CSF) and erythropoietin (EPO) on granulopoiesis and erythropoiesis. Indeed, the cumulative number of progenitors recovered during an 8-week period exceeded the initial input by a factor of 1.7 for granulocyte-macrophage (CFU-GM), of 3 for erythroid blast-forming units (BFU-E) and of 5.45 for CFU-E when EPO, GM-CSF and IL3 were combined. This study has confirmed that the system is able to sustain haematopoiesis for 8 weeks in a way similar to that in serum-dependent LTMC, despite diminished stromal adherent layer development which never covered more than 50% of the flask surface. We conclude that this defined SF-LTMC system provides a reproducible technique for studying human haematopoiesis.