Temporal recovery of short-term repopulating HSC subpopulations in marrow following schedule-dependent administrations of IL-1 alpha and M-CSF.

Studies were carried out to establish the temporal effects of abbreviated administrations of IL-1 and IL-1 plus M-CSF as rescue agents on multipotential and short-term repopulating hematopoietic stem cell (HSC) subpopulations in murine marrow treated with a myelosuppressive dose of 150 mg/kg 5-FU. The recovery kinetics for high-proliferative-potential colony-forming cells (HPP-CFC), CFU-S8 and -S12, and both CFU-M and CFU-G compartments were monitored over a 14-day interval in 5-FU-treated bone marrow (FUBM) following daily cytokine injections over a 4-day interval. Both IL-1 and the coadministration of IL-1 and M-CSF rapidly enhanced the recovery of the HPP-CFC in FUBM to supranormal levels and maintained these levels for extended intervals. Moreover, since M-CSF was unable to influence the recovery of the HSC subpopulations in FUBM by itself, the results of the two cytokines amounted to a synergistic effect on the recovery of the HPP-CFC in FUBM and a reduction of severe neutropenia in the myelosuppressed animal. Scheduling studies demonstrated that these synergistic effects were restricted to those schedules in which M-CSF was coadministered with IL-1 during the first 2 days of cytokine rescue. Finally, the recovery curves generated for the HSC and CFU-M subpopulations in response to IL-1 (with or without M-CSF) also suggest that these cytokines may conceivably alter the normal balance between proliferation and differentiation within CFU-S8 and -S12 during the accelerated recovery of hematopoiesis in FUBM.