HOST CONDITIONING WITH 5-FLUOROURACIL AND KIT-LIGAND TO PROVIDE FOR LONG-TERM BONE-MARROW ENGRAFTMENT

Administration of kit-ligand (KL) before and after doses of 5-fluorour acil (5-FU) results in marrow failure in mice, presumably because of e nhanced KL-induced cycling of stem cells, which makes them more suscep tible to the effects of 5-FU. In attempt to capitalize on this effect on stem cells, we studied the ability of KL and 5-FU to allow stable d onor engraftment of congenically marked marrow in a C57BL/6 (B6) mouse model. KL was administered subcutaneously at 50 mu g/kg, 21 hours and 9 hours before and 3 hours after each of two doses of 5-FU (125 mg/kg ) given 7 days apart to BG-recipients. Animals then received three inj ections of 10(7) congenic B6-Gpi-1(a)-donor bone marrow cells at 24, 4 8, and 72 hours after the second 5-FU dose. A separate group of animal s received a single dose of either 1 x 10(7) or 3 x 10(7) donor marrow cells 24 hours after the last 5-FU dose. The level of engraftment was measured from Gpi-phenotyping at 1, 3, 6, and 8 months in red blood c ells (RBCs) and at 8 months by phenotyping cells from the thymus, sple en, and marrow. Percent donor engraftment in RBCs appeared stable afte r 6 months. The percent donor engraftment in RBCs at 8 months was sign ificantly higher in KL + 5-FU prepared recipients (33.0 +/- 2.7), comp ared with 5-FU alone (18.5 +/- 2.6, P < .0005), or saline controls (17 .8 +/- 1.7, P < .0001). In an additional experiment, granulocyte colon y-stimulating factor (100 mu g/dose) was added to a reduced dose of KL (12.5 mu g/dose); engraftment was similar to KL alone. At 8 months af ter transplantation the levels of engraftment in other tissues such as bone marrow, spleen, and thymus correlated well with erythroid engraf tment to suggest that multipotent long-term repopulating stem cells ha d engrafted in these animals. There are concerns for the toxicity of t otal body irradiation (TBI)- or busulfan-based regimens in young recip ients of syngeneic or transduced autologous marrow who are transplante d for correction of genetic disease. In these recipients complete dono r engraftment may not be needed. The results with KL and 5-FU are enco uraging for the further refinement of non-TBI, nonbusulfan techniques to achieve stable mixed chimerism. (C) 1997 by The American Society of Hematology.