Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is used to treat a variety of malignant and non-malignant disorders, and involves the transfer of stem cells from the bone marrow, blood, or umbilical cord from a non-identical donor. The widespread application of this procedure is limited by the high rate of graft-versus-host disease (GVHD), a life-threatening condition that is mediated by alloreactive T cells from the transplant. Improving the procedure is dependent on identifying the mechanisms that contribute to this damaging T cell reactivity. We previously demonstrated in a preclinical mouse model of allo-HSCT that the autophagy protein ATG16L1 is essential for preventing intestinal inflammation and GVHD. Autophagy is a process by which cytosolic material is delivered to the lysosome for degradation, and is involved in maintaining cellular and tissue homeostasis. Additionally, a common polymorphism in ATG16L1 leading to a coding change (T300A) is associated with susceptibility to inflammatory bowel disease (IBD) and transplant-related mortality in allo-HSCT patients. Given the high prevalence of the T300A variant and the challenges associated with treating intestinal GVHD, addressing the mechanism by which ATG16L1 and autophagy protect against intestinal damage is a research priority. During the previous funding period, we made significant progress by demonstrating that ATG16L1 prevents necroptosis in intestinal epithelial cells (IECs) following allo-HSCT. Necroptosis is a form of programmed necrosis that has received attention as a therapeutic target for limiting the tissue damage observed in a range of inflammatory diseases. Our findings suggest that the intersection between autophagy and necroptosis can be targeted to treat GVHD, especially in high risk patients such as individuals harboring the ATG16L1T300A variant. However, the molecular basis for the interaction between ATG16L1 and necroptosis is obscure, and the upstream signals that trigger the adverse signaling events require examination. Thus, we lack detailed mechanistic understanding of the inflammatory process that is necessary to apply such strategies to allo-HSCT recipients. The goal of this proposal is to how ATG16L1 and autophagy integrate IEC-intrinsic and -extrinsic signals to block necroptosis following allo-HSCT, and determine how the T300A variant disrupts this protective function. We anticipate this knowledge will yield significant insight into GVHD pathogenesis and inform intervention strategies for improving allo-HSCT outcome.