A murine model of antimetabolite-based, submyeloablative conditioning for bone marrow transplantation: Biologic insights and potential applications

Nonmyeloablative conditioning regimens for marrow transplantation are desirable in many settings. Because repeated doses of the antimetabolite 5-fluorouracil (5-FU) decreases marrow long-term repopulating ability (LTRA) upon transplantation into lethally irradiated hosts, we hypothesized that mice given sequential doses of 5-FU (termed paired dose 5-FU) may permit substantial syngeneic marrow engraftment. C57Bl/6 or X-linked chronic granulomatous disease (X-CGD) mice were administered 5-FU (150 mg/kg) on days -5 and -1. Assessment of host marrow phenotype and repopulating ability occurred on day 0. Transplantation of syngeneic donor marrow occurred on day 0 or day +15. We confirmed that the number of Sca-1 ⁺lin ^- cells and the LTRA of marrow from paired dose 5-FU-treated animals were diminished. C57Bl/6 hosts conditioned with paired doses of 5-FU followed by transplantation of 20 × 10 ⁶ fresh B6.SJL marrow cells on day 0 displayed 44.9% ± 7.1% donor chimerism 2 months posttransplant, and 34.4% ± 8.6% donor chimerism 6 months posttransplant. In contrast, paired dose 5-FU-conditioned hosts transplanted with similar numbers of donor cells on day +15 exhibited only 3.4% ± 1.2% donor chimerism at 2 months. Paired dose 5-FU-conditioned X-CGD hosts transplanted with MSCV-m91Neo-transduced X-CGD marrow averaged 6.6% ± 2.3% (range, 4%-10%) NADPH oxidase-reconstituted neutrophils 12-16 months after transplant. These findings support the concept that impairment of host stem cell competitiveness may be an important mechanism for permitting engraftment of donor cells, and suggest that only a brief period of modest host stem cell impairment may be necessary to achieve substantial donor cell engraftment.