Abstract: BACKGROUND: Allosensitization is a major risk factor for graft failure in clinical bone marrow transplantation, even with an human leukocyte antigen (HLA)-matched combination under radiation-based conditioning regimens. The critical components of immunological memory in donor bone marrow graft rejection in allosensitized hosts remain unclear at present. METHODS: C57BL/6-recipient mice, which had been intraperitoneally injected with splenocytes from donor C3H mice on day -35 (sensitized recipients), had been lethally irradiated with 10-Gy whole-body irradiation and were intravenously injected with T-cell-depleted bone marrow cells (TCD-BMC) from C3H mice or third-party SJL mice. RESULTS: Lethally irradiated recipient mice, which had been sensitized by donor splenocytes 5 weeks before the transplantation of TCD-BMC, completely rejected the donor-BMC in a donor-specific manner, whereas none of the nonsensitized recipient mice, all of which showed full allogeneic chimerism, rejected the donor TCD-BMC. Antibody-mediated T cell and/or Natural Killer (NK) cell depletion did not improve the ability of the sensitized recipients to overcome the rejection even when a megadose of TCD-BMC was administered to the sensitized recipients. Furthermore, BMC rejection occurred in sensitized B cell-deficient mice. In adoptive transfer experiments, naive mice, which received a transfer of purified T cells from sensitized mice, rejected the donor BMC, but not those from nonsensitized mice. Moreover, naive mice, which received a transfer of serum containing antidonor immunoglobulin, rejected the donor BMC. CONCLUSIONS: These findings suggest that alloreactive memory T cells and antidonor immunoglobulin independently function to reject donor BMC in sensitized recipients.
