The p55 TNF-α receptor plays a critical role in T cell alloreactivity

TNF-α is known to be an important mediator of tissue damage during allograft rejection and graft-vs-host disease (GVHD), but its role in supporting T cell responses to allogeneic Ags is unclear. We have studied this question by comparing normal mice with those lacking the p55 (p55 TNFR(- /-)) or p75 (p75 TNFR(-/-)) TNF-α receptors as donors in well-defined bone marrow transplant (BMT) models. Recipients of p55 TNFR(-/-) cells had significantly reduced mortality and morbidity from GVHD compared with the other two sources of T cells. In vitro, T cells lacking the p55 (but not the p75) TNF-α receptor exhibited decreased proliferation and production of Th1 cytokines in MLC. This defect was only partially restored by exogenous IL-2 and affected both CD4⁺ and CD8⁺ populations. CD8⁺ p55 TNFR(-/-) proliferation was impaired independently of IL-2 whereas CTL effector function was impaired in an IL-2-dependent fashion. Inhibition of TNF-α with TNFR:Fc in primary MLC also impaired the proliferation and Th1 differentiation of wild-type T cells. BMT mixing experiments demonstrated that the reduced ability of p55 TNFR(-/-) donor cells to induce GVHD was due to the absence of the p55 TNFR on T cells rather than bone marrow cells. These data highlight the importance of TNF-α in alloreactive T cell responses and suggest that inhibition of the T cell p55 TNF-α receptor may provide an additional useful therapeutic maneuver to inhibit alloreactive T cell responses following bone marrow and solid organ transplantation.