Abstract Bone Marrow Transplantations (BMT) can be curative for a variety of hematologic malignancies but Graft Versus Host Disease (GVHD), an immune reaction of donor cells against the host, remains the deadliest risk of this therapy. T lymphocytes drive an inflammatory response in the host that can result in organ damage and destruction, and even death of the transplant recipient. While broad immunosuppressants are given to prevent and treat GVHD, it still results in the mortality of up to 50% after diagnosis. GVHD occurs in two forms, acute and chronic, that differ in their time to development as well as pathology. There is a need for more targeted therapies to prevent GVHD, while still maintaining the protective immune functions against pathogens and malignant relapse. We have used our highly translationally relevant non-human primate (NHP) model of GVHD to identify genes upregulated in T cells in target organs of GVHD. Through transcriptomic pathway analysis we have identified inhibitor of DNA-binding 2 (ID2) as a key upstream regulator of many genes activated in the destruction of target organs during GVHD. In the literature Id2 is involved in regulating T cell differentiation, but how this occurs and how it affects the functionality of T cells in the context of GVHD remains unknown. This project aims to understand how ID2 deletion in T cells affects their ability to differentiate into Type 1 and 17 (Th/c 1 and Th/c 17) T cells which drive GVHD and regulatory T cells (Treg) which prevent GVHD. We will use CRISPR/Cas9 to first delete ID2 in type 1 and 17 T cells and explore their functionality in vitro and in GVHD models. We will also assess how the regulatory landscape of ID2-edited T cells changes at baseline and in the context of GVHD through transcriptomic profiling. Second, we will delete ID2 from Treg cells to determine the effects of id2 in maintaining their suppressive activity. And we will evaluate the ability of ID2-delteted Treg cells to control GVHD, especially in cGVHD where Tregs play a vital role in suppressing conventional T cells in the long term. Targeting the pathogenicity of type 1 and 17 T cells while sparing the protective effects of T regulatory cells remains a challenge in the BMT field and the literature suggests that targeting ID2 may tip both towards tolerance. This project will be important in understanding better the role of ID2 in T cell differentiation and how targeting ID2 may represent a novel therapeutic strategy for controlling or treating GVHD.

Summary Statement Bone marrow transplantation can be curative for cancers of the blood and other hematologic diseases. The greatest risk for death after a bone marrow transplant is a complication known as “graft verses host disease” (GVHD), in which T cells transplanted with the bone marrow graft attack the organs and tissues of the transplant recipient, causing organ damage and even death. Current therapies to prevent GVHD are broadly immunosuppressive and can leave patients prone to infections and malignancies which is why this project seeks to investigate how targeting specific T cell regulatory pathways could prevent GVHD without limiting the other protective functions of the immune system.