Transplantation of allogeneic bone marrow (BM) is often complicated by the development of acute graft-vs-host disease (GVHD) caused by contaminating T cells in BM inocula because of activation of the host reactive T effector cells. Using a murine model for acute GVHD caused by injection of parental C57Bl/6 splenocytes into unirradiated (C57Bl/6 x DBA/2) F1 hybrids, we demonstrated that pretreatment of the inocula with a novel immunosuppressant, B subunit of cholera toxin (CT-B) impaired the ability of C57Bl/6 T cells to induce acute GVHD in F1 recipients. F1 mice injected with CT-B-treated C57Bl/6 splenocytes did not develop significant splenomegaly, and no antihost CTLs were found in their spleens. Moreover, these mice did not suffer from aplastic anemia, nor from general immunosuppression. Immunofluorescence studies suggest that treatment of the inducing inocula with CT-B selectively prevents accumulation of the host-reactive CD8+ T cells in F1 mice. Furthermore, our experiments demonstrated that CT-B treatment does not impair the ability of BM progenitors to form colonies in semisolid culture or in lethally irradiated hosts. Thus, taken together, our data suggest that ex vivo CT-B treatment can be used in allogeneic BM transplantation to prevent acute GVHD.

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