CD127-LOW MEMORY T CELLS AND IMMUNOGLOBULIN M ARE CRITICAL FACTORS FOR EARLY REJECTION OF ALLOGENIC BONE MARROW CELLS IN SENSITIZED RECIPIENT MICE.

Abstract

Listen

Translate article

O270 Aims: Allosensitization is major risk factor of graft failure in clinical bone marrow transplantation even in HLA-matched combination. It is still unclear what critical components of immunological memory act on graft rejection in allosensitized hosts. In this study, we investigated the impact of allosensitization on engraftment of donor bone marrow cells (BMC) and the key effectors in donor BMC-rejection using the conventional fully allogeneic murine bone marrow transplantation model. Methods: We used C57BL/6 recipient mice (B6; H-2Kb), which were intraperitoneally injected with 1×107 splenocytes of C3H (H-2Kk) mice on day -35 (5W-sensitized) or -7 days (1W-sensitized), as allosensitized recipients. The B6 recipient mice were lethally irradiated with 10 Gy whole-body irradiation (WBI) and were intravenously injected with 2×107 (low dose) or 10×107 (high dose) T-cell-depleted bone marrow cells (TCD-BMC). Results: The titer of IgG alloAb in sensitized B6 were peaked at 4-7 weeks after allosensitization. The titer of IgM alloAbs arrived at maximum level within the 5 days and rapidly decreased to undetectable level within 3 weeks. While all non-sensitized recipients transplated with TCD-BMC from C3H survived permanently {Mean survival time (MST) >100 days}, all 5W-sensitized recipients did not survived (MST=10.2 days). We confirmed the cause of death was not due to Graft-versus-Host disease. The rejection of BMC was donor-specific since all 5W-sensitised recipients reconstituted with third party, SJL(H-2s)-TCD-BMC survived permanently (MST >100 days). This rejection of BMC was not overcame by administration of high dose TCD-BMC or by antibody-mediated NK-cell-depletion. In spite of existence of high titer of IgG alloAb, antibody-mediated T-cell-depletion alone can improve the rejection (MST=53.9 days), but, in case using low dose TCD-BMC, late graft failure occurred in 5W-sensitized recipients mice. Antibody-mediated T-cell-depletion and using high-dose of TCD-BMC completely overcame the early and late graft rejection (MST>100 days) and the recipients had durable multilineage complete chimerism. We confirmed that radioresistant T cells were critical components to reject donor BMC using adoptive transfer model. The phenotype of surviving T cells after lethal irradiation was CD127-low CD44-high memory T cells. In contrast to 5W-sensitized B6, 1W-sensitized B6, rejected C3H-BMC in spite of the depletion of NK-cells or T-cells. To assess the effect of alloreactive IgM, naïve mice transferred with serum from B6 mice, which had been allosensitized five days before (5D-serum: high IgM and minimal IgG alloAb), or five weeks before (5W-serum: no IgM and high IgG alloAb), were lethally irradiated and transplanted with donor BMC. The recipients transferred with 5D-serum rejected donor BMCs (MST=8.6 days), but the recipients transferred with 5W-serum did not (MST>100 days). Conclusions: These findings suggested that alloreactive CD127-low memory T cells and IgM are the key effector for the rejection of donor BMCs in sensitized recipients.