Engineering T cells to suppress acute GvHD and leukemia relapse after allogeneic hematopoietic stem cell transplantation.

Acute graft-versus-host disease (GvHD) limits the therapeutic benefit of allogeneic hematopoietic stem cell transplantation (allo-HSCT) and requires immunosuppressive prophylaxis that compromises anti-tumor and anti-pathogen immunity. OX40 is a costimulatory receptor upregulated on circulating T-cells in acute GvHD and plays a central role in driving the expansion of alloreactive T-cells. Here, we show that OX40 is also upregulated on T-cells infiltrating GvHD target organs in a rhesus macaque model, supporting the hypothesis that targeted ablation of OX40+ T-cells will mitigate GvHD pathogenesis. We thus created an OX40-specific cytotoxic receptor that, when expressed on human T-cells, enables selective elimination of OX40+ T-cells. Because OX40 is primarily upregulated on CD4+ T-cells upon activation, engineered OX40-specific T-cells mediated potent cytotoxicity against activated CD4+ T-cells and suppressed alloreactive T-cell expansion in a mixed lymphocyte reaction model. OX40 targeting did not inhibit anti-viral activity of memory T-cells specific to EBV, CMV, and adenoviral antigens. Systemic administration of OX40-targeting T-cells fully protected mice from fatal xenogeneic GvHD mediated by human PBMCs. Further, combining OX40 targeting with a leukemia-specific chimeric antigen receptor (CAR) in a single T-cell product provides simultaneous protection against leukemia and acute GvHD in a mouse xenograft model of residual disease post-transplant. These results underscore the central role of OX40+ T-cells in mediating acute GvHD pathogenesis and support the feasibility of a bi-functional engineered T-cell product derived from the stem cell donor to suppress both disease relapse and acute GvHD following allo-HSCT.