Dissociating GVT from GVHD in Murine BMT Models through TNFα Dependent CD4+ T Cell Mediated GVHD and IFNγ Dependent CD8+ T Cell Mediated Anti-Tumor Effects.

Tumor relapse and acute graft-versus-host disease (GVHD) remain the major obstacles limiting the efficacy of allogeneic bone marrow transplantation (allo-BMT). However, there has been a strong correlation between the beneficial graft-vs.-tumor effects (GVT) and the deleterious GVHD. Recent studies have provided novel evidence for the divergent roles of the cytokines IL-17 and IFNγ in the establishment and maintenance of inflammatory disease. Because proinflammatory responses are greatly involved in the pathogenesis of acute GVHD, we examined the role of CD8+ T cell-derived IFNγ and CD4+ T cell-derived TNFα mediated cytokine response in the development of GVHD/GVT in two different murine BMT/GVHD models as well a delayed bortezomib-induced GVHD dependent gut toxicity model that we have shown to be associated with increased serum levels of IL-1, IL-6 and TNFα (Blood, 2005). We found that removal of CD4+ but not CD8+ T cells from donor graft markedly lowered post-transplant serum TNFα but not IFNγ levels. This correlated with significantly decreased acute GVHD as well as delayed bortezomib-induced GVHD dependent gut toxicity. The use of TNFα knockout mice as donors revealed that the delayed bortezomib exacerbated acute GVHD-dependent mortality was dependent on CD4+ T cell-derived TNFα. In addition, we found that donor CD4+ IL-17+ cells were significantly increased in the GVHD target organs (gut and liver) but not the spleen of acute GVHD mice. Donor CD4+ IL-17+ cells in the gut were further increased in delayed bortezomib-induced GVHD dependent gut toxicity model. Thus, removal of CD4+ T cells from the graft significantly altered post-transplant serum cytokine patterns resulting in reduced acute GVHD lethality as well as delayed bortezomib-induced GVHD dependent mortality. To determine the effect of bortezomib treatment on CD8+ T cell mediated GVT, A20 lymphoma bearing BALB/c recipients were given FvB cellular grafts. No significant protective anti-tumor effects of the BMT alone with or without post-transplant bortezomib therapy were observed in these advanced-tumor-bearing recipients. When the tumor-bearing mice received allogeneic BMT with donor splenocytes that were depleted of CD4+ T cells, marked and significant increases in survival were observed, indicating that significant GVT effects had been obtained in the absence of donor CD4+ T cells. Survival was further improved with the addition of prolonged post-transplant bortezomib therapy, indicating synergistic anti-tumor responses had been obtained with CD4+ T cell depleted spleen cells and bortezomib treatment (P < 0.05). The use of IFNγ deficient mice, as donors of CD8+ enriched T cells, revealed that the GVT activity and bortezomib-enhanced GVT responses in this model was dependent on donor CD8+ T cell-derived IFNγ. These data suggest that selection for a CD8+ T cell mediated IFNγ but not CD4+ T cell mediated TNFα cytokine response may be a novel therapeutic target for the separating GVT from acute GVHD.