Maternal Administration of Busulfan before in Utero Hematopoietic Cell Transplantation Improves Congenic Bone Marrow Cell Engraftment in a Murine Model.

In utero hematopoietic cell transplantation (IUHCT) is a nonmyeloablative procedure that leads to donor cell chimerism and donor-specific tolerance. However, most clinical applications of IUHCT have failed because of low levels or even no engraftment of donor cells in immunologically normal fetuses. It is likely that the competition from the host hematopoietic compartment is the primary barrier to successful IUHCT, suggesting that conditioning methods that provide a competitive advantage to donor cells may lead to higher-level engraftment following IUHCT. This study aimed to research whether maternal administration of low-dose total body irradiation (TBI) or busulfan (BU) before IUHCT may result in increased donor cell chimerism in postnatal bone marrow transplantation in a congenic murine model. We first determined the birth and mortality rates after maternal administration of low-dose TBI (0, 2 or 4 Gy) or BU (5, 10, 15, or 20 mg/kg) before IUHCT in B6 mice. The mice that received 2 Gy TBI plus IUHCT showed significantly lower birth rate (23.3%) and a 100% 3-day mortality rate. The mice that received 10 mg/kg BU plus IUHCT had similar birth and 3-day mortality rates (58.6% and 0%) compared to mice that received IUHCT alone (61.1% and 4.55%). We then performed maternal administration of BU at 1 of 3 dosages (5, 10, or 15 mg/kg) at 24 hours before intrauterine transplantation of 2.5 × 10 B6GFP Sca-1 bone marrow cells (BMCs) or 2.5 × 10 B6GFP BMCs on gestational day 14 (E14). Green fluorescent protein (GFP) chimerism in peripheral blood mononuclear cells (PBMCs), RBCs, and platelets of mice at 4 weeks of age was enhanced significantly with an increase in BU dose. Moreover, GFP chimerism of PBMCs from the B6GFP BMC group was significantly higher than that of the B6GFP Sca-1 BMC group (22.56% versus 7.20%; P = .018). Finally, the pregnant mice were treated with 10 mg/kg of BU at E13, E14, or E15, followed by intrauterine transplantation of 2.5 × 10 B6GFP BMCs 24 hours later. Except for the short-term level of chimerism in PBMCs, which showed no significant difference among the 3 study groups, the results indicate that both short-term (age 4 weeks) and long-term (age 14 weeks) engraftment in PBMCs, RBCs, and platelets was higher in group E16 compared with groups E14 and E15. We also discovered that the engraftment was stable, multilineage, and increased with time. In conclusion, maternal administration of BU, but not of TBI, along with IUHCT could significantly enhance engraftment in a congenic murine model.