GRAFT-VERSUS-HOST REACTIVITY AND GRAFT-VERSUS-LEUKEMIA EFFECT IN MURINE ALLOGENEIC BONE MARROW CHIMERAS CONDITIONED WITH TOTAL BODY IRRADIATION OR TOTAL LYMPHOID IRRADIATION1

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Abstract
To investigate whether graft-versus-host reactivity (GVHR) and the graft-versus-leukemia (GVL) effect can be differentiated, C3H-->AKR mixed bone marrow (BM) chimeras were prepared using two different conditioning regimens. Total body irradiation (TBI) chimeras were induced by infusing 5 x 1O(6) T cell depleted syngeneic AKR BM cells together with 15 x 1O(6) non T cell depleted allogeneic C3H BM cells 1 day after a single fraction of 10.5 Gy TBI. Total lymphoid irradiation (TLI) chimeras were prepared by injecting only 15 x 10(6) non T cell depleted C3H BM cells after 10 daily fractions of 2 Gy TLI Both groups of chimeras were healthy, without clinical or histological signs of graft-versus-host disease (GVHD). In both groups, clonal deletion of antihost-reactive donor type T lymphocytes was found. Whereas TBI chimeras did resist rejection by host type splenocytes injected 2 months after transplantation, TLI chimeras did not. As the latter phenomenon is believed to reflect remaining GVHR, TLI chimeras did have a lower remaining GVHD capacity than TBI chimeras. Nevertheless, TLI chimeras survived significantly longer after host type leukemia challenge (injection of 6 x 10(6) AKR lymphoma cells). The better survival of the TLI chimeras was not due to the radiation regimen, because TLI or TBI conditioned syngeneic AKR-->AKR BM recipients did succumb equally rapidly after AKR lymphoma injection. Donor type (CM) lymphokine-activated killer cell activity, however, was higher in TLI chimeras and may explain the better GVL activity in TLI mice. This model thus illustrates that GVHD and GVL effects can be dissociated and are differentially influenced by the conditioning regimen used for BM transplantation.