TRANSFORMING-GROWTH-FACTOR-BETA-1 DELAYS FORMATION OF GRANULOCYTE-MACROPHAGE COLONY-FORMING CELLS, BUT SPARES MORE PRIMITIVE PROGENITORS DURING EX-VIVO EXPANSION OF CD34(+) HEMATOPOIETIC PROGENITOR CELLS

Ex vivo culture and expansion of autologous haemopoietic transplants h as been developed to improve tumour cell purging and accelerate haemop oietic reconstitution by transplantation of increased progenitor cell numbers. We studied the effect of the negative haemopoietic regulator, transforming growth factor beta-1 (TGF-beta 1) on primitive precursor s during ex vivo expansion of CD34(+) cells, When added directly to me thylcellulose colony-forming assays, TGF-beta 1 potently suppressed th e development of granulocyte-macrophage colonies from CD34(+) enriched peripheral blood progenitor cells (80-90% inhibition). In contrast, e xpansion of total nucleated cells and granulocyte-macrophage colony-fo rming cells (GM-CFC) from CD34(+) progenitors in liquid culture in the presence of stem cell factor (SCF), interleukin (IL)-1 beta, IL-3, IL -6 and erythropoietin (EPO) was inhibited to 32-65% of control culture levels within 14 d when TGF-beta 1 was added, and still produced an a verage 3.3-fold absolute amplification of GM-CFC. The inhibitory effec t of TGF-beta 1 on GM-CFC generation was reversed when it was washed o ut on day 6 of ex vivo expansion cultures, and total numbers of GM-CFC generated from expansion cultures then reached levels of untreated co ntrols by day 16. Long-term bone marrow culture-initiating cell (LTCIC ) numbers were preserved, at least at input levels, over a culture per iod of 14 d both in control and TGF-beta-1-treated expansion cultures. These findings suggest that TGF-beta 1, a cytokine which induces apop tosis or terminal differentiation in a number of malignant cell types, may be added to ex vivo expansion cultures without loss of primitive cells from autologous haemopoietic transplants.