A Novel RIPK1 Inhibitor Reduces GVHD in Mice via a Non-immunosuppressive Mechanism that Restores Intestinal Homeostasis.

Intestinal epithelial cells (IECs) are implicated in the propagation of T cell-mediated inflammatory diseases including graft-versus-host disease (GVHD), but the underlying mechanism remains poorly defined. Here, we report that IECs require receptor-interacting protein kinase-3 (RIPK3) to drive both gastrointestinal (GI) tract and systemic GVHD following allogeneic hematopoietic stem cell transplantation. Selectively inhibiting RIPK3 in IECs markedly reduces GVHD in murine intestine and liver. IEC RIPK3 cooperates with RIPK1 to trigger MLKL-independent production of T cell-recruiting chemokines and MHC class II molecules which amplify and sustain alloreactive T cell responses. Alloreactive T cell-produced IFN-γ enhances this RIPK1/RIPK3 action in IECs through a JAK/STAT1-dependent mechanism, creating a feed-forward inflammatory cascade. RIPK1/RIPK3 complexes with JAK1 to promote STAT1 activation in IECs. The RIPK1/RIPK3-mediated inflammatory cascade of alloreactive T cell responses results in intestinal tissue damage, converting the local inflammation into systemic syndrome. Human patients with severe GVHD showed highly activated RIPK1 in the colon epithelium. Finally, we discover a selective and potent RIPK1 inhibitor (Zharp1-211) that significantly reduces JAK/STAT1-mediated expression of chemokines and MHC class II molecules in IECs, restores intestinal homeostasis and arrests GVHD without compromising the graft-versus-leukemia (GVL) effect. Thus, targeting RIPK1/RIPK3 in IECs represents an effective non-immunosuppressive strategy for GVHD treatment and potentially for other diseases involving GI tract inflammation.