ID3 regulation of tissue-infiltrating T cells mediating graft-versus-host disease and leukemia rejection - PROJECT SUMMARY Graft-versus-host disease (GVHD) and the sequelae of immunosuppression have been a major barrier to the success of allogeneic hematopoietic stem cell transplantation (allo-HSCT), which can potentially cure hematological cancers such as leukemia, lymphoma and myeloma. GVHD is caused by donor T cells that attack recipient’s non-hematopoietic-lymphoid tissues (non-HLTs), including gastrointestinal (GI) tract, liver and skin. Advanced strategies with more aggressive immunosuppression agents can better control GVHD. Consequently, cancer relapse becomes the major cause of deaths (>50%) in allo-HSCT patients. Persisting alloreactive donor T cells in non-HLTs are known a determinant of GVHD. Indeed, we recently discovered that inhibition of RIPK1/RIPK3 activity in the GI tract reduces both local and systemic GVHD. These observations together with others highlight an urgent need of better defining how GVHD is locally maintained. A hallmark of tissue-infiltrating alloreactive T cells is their capacity to persist and function in response to persistent alloantigens. They show tissue-resident memory T cell features, contain a subset of Tcf1+ progenitor-like T cells (Tcf1+ TPRO) with a great ability to self-renew, and have acquired unique transcriptional programs for local tissue residence. However, the transcriptional regulators that control these processes remain poorly defined. We recently demonstrate that Id3, a transcription regulator important for CD8+ T cell memory response, has dual functions in maintaining alloreactive T cell responses during GVHD. Id3 restrains excessive PD-1 expression and effector differentiation of alloreactive T cells, but promotes the persistence of both Th1 effector T cells and Tcf1+ TPRO cells that infiltrate non-HLTs. Donor T cells lacking Id3 fail to mediate severe GVHD. PD-1 blockade restores the capacity of Id3- ablated donor T cells to induce GVHD. Id3 represses expression of transcription factors, which promote PD-1 transcription and exuberant effector differentiation of activated T cells, but sustains expression of Tcf1 protein, which is required for self-renewal of memory T cells. Building on these findings, we hypothesize that Id3 regulates the formation and maintenance of tissue-infiltrating Tcf1+ TPRO cells that are critical for GVHD maintenance and leukemia control through coordinating the expression of genes engaged in effector differentiation and memory T cell development. Two specific aims are proposed to test this hypothesis. Aim 1 will define the effect of alloreactive Tcf1+ TPRO cells in GVHD maintenance and leukemia control and characterize the central role of Id3 in these T cells. Aim 2 will establish the beneficial effects of ID3-engineered chimeric antigen-receptor (CAR) T cells on eliminating leukemia. Our findings will provide novel molecular insights into biology of tissue-infiltrating alloreactive T cells and lead to novel Id3 targeting-based non-HLT-specific approaches to reduce GVHD without global immune suppression. They will also identify the molecular requirement for CAR T cells to sustain T cell stemness and to resist exhaustion differentiation, thereby enhancing the efficacy of cancer immunotherapy using CAR T cells.
