CONDITIONS THAT SUPPORT LONG-TERM PRODUCTION OF OSTEOCLAST PROGENITORS IN-VITRO

To better understand the mechanisms of osteoclast precursor developmen t from hematopoietic stem cells, we examined the conditions that suppo rt the production of osteoclast progenitors, osteoclast colony-forming units (CFU-O), from long-term bone marrow cultures established under myeloid (Dexter's) and lymphoid (Whitlock and Witte's) conditions. Non adherent cells harvested weekly from myeloid or lymphoid long-term cul tures were assayed for CFU-O-derived colony formation in agar in the p resence of a murine osteoclast colony-stimulating factor. The myeloid system supported CFU-O production for weeks, but the system produced m any other types of myeloid colonies and cells as well, and quantificat ion of CFU-O-derived colonies was difficult, The lymphoid long-term cu lture system also produced CFU-O; however, CFU-O production in the lym phoid system appeared more selective than in the myeloid system, but w as transient, Interestingly, the addition of medium containing G-CSF t o these cultures greatly enhanced (>200%) the CFU-O production, This e nhanced CFU-O production was confirmed using hone marrow cultures esta blished on a defined marrow stromal cell line under lymphoid condition s and supplemented with recombinant murine G-CSF. Thus, G-CSF facilita tes the development of clonogenic osteoclast progenitors from hematopo ietic stem cells in lymphoid long-term culture conditions, This cultur e system may serve as a useful model for ex vivo generation of osteocl ast progenitors.