TRANSFORMING GROWTH-FACTOR-BETA REGULATES THE CELL-CYCLE STATUS OF INTERLEUKIN-3 (IL-3) PLUS IL-1, STEM-CELL FACTOR, OR IL-6 STIMULATED CD34+ HUMAN HEMATOPOIETIC PROGENITOR CELLS THROUGH DIFFERENT CELL KINETICMECHANISMS DEPENDING ON THE APPLIED STIMULUS

The immediate cell kinetic response of highly purified human bone marr ow progenitor cells (CD34(+) sorted fraction) to the inhibitory effect s of transforming growth factor-beta (TGF-beta) was studied using the BrdU-Hoechst flow-cytometric technique. The progenitor cells were stim ulated with either interleukin-3 (IL-3) alone or with IL-3 in combinat ion with IL-1, stem cell factor (SCF), or IL-6, and the inhibitory act ion of TGF-beta was evaluated in each phase of the first three consecu tive tell cycles. Semisolid methylcellulose cultures were also perform ed to compare these initial events to the effects observed after 7, 14 , and 21 days of incubation. Within the CD34(+) compartment, the proge nitor cells can be discriminated on a functional basis, i.e., in terms of TGF-beta sensitivity. Very primitive progenitors, recruited out of the G(0) phase by IL-3 plus an early-acting factor (IL-1, SCF) are, u pon addition of TGF-beta, arrested specifically in the G(1) phase of t he second cell cycle. In the clonogenic assays, the increased colony f ormation due to IL-1 or SCF was completely abolished by the counteract ing effect of TGF-beta that diminished colony output back to the level of TGF-beta-plus-IL-3 supplemented colony growth. Addition of TGF-bet a to CD34(+) progenitors responding to IL-3 alone resulted in an overa ll retardation, but without an apparent specific accumulation of cells in any of the cell cycles. Finally, within the CD34(+) compartment, t here exists a subset of IL-3-responsive, but TGF-beta-insensitive, pro genitor cells that were, upon addition of TGF-beta, not arrested at al l. In conclusion, our results demonstrate that TGF-beta exerts differe nt cell kinetic effects on CD34(+) progenitor cell growth depending on the applied stimulus.