Project 2: Elucidating how TIGIT agonists regulate CNS autoimmunity exacerbated by PD-1 blockade

The immunoinhibitory receptors PD-1 and TIGIT play critical roles in regulating tolerance and are key mediators of T cell dysfunction in cancer. We, along with our collaborators in this PPG, have shown that PD-1:PD-L1 interactions regulate peripheral T cell tolerance and TIGIT has T cell-intrinsic inhibitory effects that mediate regulatory T (Treg) cell function. Based on our new preliminary data showing PD-1 blockade increases the frequency of TIGIT+ Treg cells and data of Project 3 showing that TIGIT agonist reversed in vitro defects of Treg function in MS, we tested if TIGIT agonism could control pathogenic T cells and ameliorate autoimmunity exacerbated by PD-1 blockade using the EAE model. Remarkably, TIGIT agonist mAb diminished EAE severity in mice given anti-PD-1 blocking mAb to a greater extent than TIGIT agonism alone. Importantly, TIGIT agonism combined with PD-1 blockade did not impair efficacy of PD-1 blockade in controlling tumors, suggesting TIGIT as a potential target for treating immune-related adverse events (irAEs) associated with PD-1 blockade therapy. The goal of Project 2 is to determine how interactions between the TIGIT/CD155 and PD-1/PD-L1 pathways control CD4+ Treg and CD4+ FoxP3— T cells, and define the cellular and molecular circuits underlying these interactions. In Aim 1, we will test the hypothesis that cellular and molecular interactions between PD-1 and TIGIT control Treg and CD4+ FoxP3—T cells to regulate autoimmunity. We will use novel tools and approaches developed by PPG investigators, including TIGIT agonist antibodies, TIGIT and PD-1 conditional knockout (KO) mice that restrict deletion to specific T cell types, high-dimensional cytometry, single- cell RNA sequencing (scRNAseq), spatial transcriptomics and gene perturbation approaches to interrogate cellular and molecular mechanisms. In Aim 2, we will test the hypothesis that interactions between CD155 and PD-L1 on APC and tumors balance Treg and T effector cell functions to regulate tissue inflammation. We will evaluate functional interactions between CD155 and PD-L1, focusing on their cell-intrinsic functions in DC and tumor cells, and cell-extrinsic effects on Treg and CD4+ FoxP3— T cells, using CD155 and PD-L1 conditional KO mice that restrict deletion to DC and tumor cells lacking CD155 and/or PD-L1 or only their cytoplasmic domains, and similar approaches as in Aim 1. Our results will provide critical insights into unique and overlapping nodes by which PD-1/PD-L1 and TIGIT/CD155 interact to modulate Treg and CD4+FoxP3— cells to regulate T cell tolerance. Moreover, our results will contribute directly to Projects 1 and 3 by providing insight into bidirectional interactions between TIGIT and CD155 (Project 1) and functional differences in T cells from patients with MS or malignant gliomas based on PD-1/PD-L1 and TIGIT/CD155 expression and activity (Project 3). Understanding mechanisms of TIGIT/CD155 and PD-1/PD-L1 interactions should enable design of new therapeutic strategies for spontaneous autoimmune disorders and irAEs seen with cancer immunotherapies. We will benefit from Core A (admin), Core B (gene perturbation), and Core C (scNuc-Seq and Multi-omics).