Project 3: Role of Coinhibitory receptors in regulating Immune Tolerance in the Human Brain

Studies from our PPG have elucidated fundamental roles for PD-1/PD-L1 and TIGIT/CD155 in regulating immune tolerance in cancer and autoimmunity. Our investigations in experimental models and in humans suggest there are distinct effects of PD-1/PD-L1 and TIGIT/CD155 signaling in human Tregs with PD-1:PD-L1 interactions regulating T cell tolerance while TIGIT exhibits T cell intrinsic inhibitory effects that regulates tolerance and Treg function. Based on single-cell transcriptomic and TCR sequence analyses of tumor samples from brain tissue of patients with glioblastoma receiving αPD-1 or combinations αPD-1/αTIGIT mAb, we observed that while PD-1 blockade alone induced Treg proliferation, the combination of PD-1 & TIGIT blockade resulted in IFNγ-secreting Treg effectors which resemble dysfunctional Tregs in autoimmunity. Data from Projects 1 & 2 showed that PD-1 blockade increases the frequency of TIGIT+ Tregs and when coupled with TIGIT agonism, controlled pathogenic T cells ameliorating autoimmunity induced by PD-1 blockade. Furthermore, combination PD-1 & TIGIT blockade increases pro-inflammatory signatures in PD-L1+ and CD155+ myeloid cells without impairing the efficacy of PD-1 blockade in controlling tumors. These data suggest that TIGIT is a potential target for treating immune-related adverse events associated with PD-1 blockade. Our underlying hypothesis is that signaling through PD-1/PD-L1 and TIGIT/CD155 are distinct but synergistically coordinate Treg and myeloid cell function in a bidirectional fashion in autoimmunity and cancer. Thus, the goal of this project is to identify key pathways induced by PD-1/TIGIT signaling in human Tregs and PD-L1/CD155 signaling in human myeloid cells. To achieve these goals, we propose in aim 1 to determine how the balance of PD-1+ and TIGIT+ signaling in human Tregs modulates peripheral tolerance in health and disease states by elucidating key transcriptional pathways induced by PD-1 and/or TIGIT signaling and blockade in dysfunctional MS Tregs compared with healthy Tregs. Using brain tissue from glioblastoma patients in our clinical trial, we will identify the in vivo effects of PD-1 and/or TIGIT blockade on Treg phenotypes and clonal expansion using single-cell sequencing and spatial multi-omic technologies. In aim 2, we will determine how PD-L1+ and CD155+ signaling governs transcriptional signatures in myeloid cells by examining how alterations in PD-L1/CD155 signaling modulates myeloid cell function in MS patients in vitro. Finally, we will identify key transcriptional signatures induced in vivo by PD-L1+ and CD155+ agonist in glioblastoma generating immune-brain cell interactomes based on transcriptional signatures, which will be confirmed using spatial multi- omics. Findings from our study will guide the development of combination immune checkpoint therapies in autoimmunity and cancer and potentially provide a means to effectively administer these therapies while preventing complications of autoimmunity.