ALL-TRANS-RETINOIC ACID SHOWS MULTIPLE EFFECTS ON THE SURVIVAL, PROLIFERATION AND DIFFERENTIATION OF HUMAN FETAL CD34(+) HEMATOPOIETIC PROGENITOR CELLS

To evaluate the effect of all-trans retinoic acid (RA) on fetal haemop oiesis, we performed serum-free liquid and semisolid cultures using CD 34(+) cells purified from midtrimester human fetal blood samples. RA, at both physiological(10(-6) and 10(-11)and 10(-12)M) pharmacological (10(-6) and 10(-7)M) concentrations, significantly (P<0.01) promoted t he survival of fetal CD34(+) cells in liquid cultures from day 3 onwar ds, by suppressing apoptosis induced by serum and growth factor depriv ation. On the other hand, RA alone had no significant effect on the pr oliferation and differentiation of fetal haemopoietic progenitors. In the presence of optimal concentrations of recombinant interleukin-3 (I L-3), stem cell factor (SCF), granulocyte/ macrophage-colony stimulati ng factor (GM-CSF), and erythropoietin (Epo), low and high doses of RA induced striking differential effects on CD34(+) cell proliferation i n liquid cultures and colony formation in semisolid assays. In fact, 1 0(-11)M and 10(-12) mRA were able to: (i) significantly (P<0.05) incre ase H-3-thymidine uptake by fetal CD34(+) cells in liquid cultures, an d (ii) variably promote the growth of pluripotent (CFU-GEMM, P<0.05), early (BFU-meg) and late (CFU-meg, P<0.01) megakaryocyte, granulocyte/ macrophage (CFU-GM, P<0.01) and erythroid (BFU-E) progenitors in semis olid cultures, On the contrary, 10(-6) and 10(-7)M RA induced: (i) an overall inhibition (P<0.01) of CD34(+) cell growth in liquid cultures; (ii) a marked suppression of BFU-E colony formation (P<0.01) at all E po concentrations examined (0.002-4IU/ml); and (iii) a significant (P< 0.01) stimulation of CFU-GM with a shift from mixed granulocyte/ macro phage to pure granulocyte colonies, whereas it had little effect on th e growth of CFU-GEMM, BFU-meg and CFU-meg. Our data, as a whole, demon strate that RA has direct complex effects on the survival, growth and clonal expansion of fetal haemopoietic progenitor cells, mainly depend ing on the presence of recombinant cytokines, the type of progenitor a nd the concentrations of RA.