Abstract 1367: PD1 signaling uncovers a pathogenic subset of cytotoxic T cells
Authors: Bukhari Shoiab , Lerrer Shalom , Straube Johanna , Winchester Robert , Henick Brian , Dragovich Matthew , Mor Adam 
Published: March 2024

Abstract
PD-1 drives its fame for serving as a pivotal immune checkpoint receptor on T cells. Within the realm of cancer immunotherapy, blocking this receptor triggers the T cell activation, leading to the immune response against tumors. Conversely, in autoimmunity, PD-1 agonist is a prime candidate for effectively suppressing the T-cell-driven auto-reactivity and self-tissue damage. Despite a decade of exploration and unlike cancer immunotherapy, the efficacy of PD-1 agonists in treating autoimmunity remains a challenge. To overcome this hurdle, innovative methods must be devised to look beyond the PD-1 receptor engagement and uncover the downstream effectors involved in PD-1 signal transduction. A comprehensive genome-wide CRISPR/Cas9 screen was also conducted to pinpoint genes linked to PD-1 signaling. An in-depth exploration of genes associated with PD-1 signaling was undertaken, utilizing publicly accessible bulk and single-cell RNA sequencing datasets of patients with melanoma treated with PD-1 blockade and in patients with inflammatory arthritis. We employed flow cytometry of T cells derived from peripheral blood and synovial fluid to validate the results.Our screening process validated established regulators in the proximal PD-1 signaling pathway and unveiled an additional 1,112 unique genes associated with PD-1's capacity to hinder T-cell functions. These genes demonstrated a robust correlation with the response of cancer patients to PD-1 blockades and exhibited high scores for tumor immune dysfunction and exclusion, affirming their downstream involvement in PD-1 signaling. Functional annotation underscored the significance of these genes in established immune regulation processes. Intriguingly, T cells isolated from patients with inflammatory arthritis exhibited a significant downregulation of the same genes, emphasizing their overarching inhibitory role. Examining single-cell RNA sequencing data revealed that five specific genes, KLRG1, CRTAM, SLAMF7, PTPN2, and KLRD1, were notably downregulated in activated and effector T cells from synovial fluids. Back-gating these genes to canonical cytotoxic T cell signatures identified PD-1+ HLA-DRHIGH KLRGLOW T cells as a novel inflammatory T cell subset that should be targeted with immunotherapies. Our findings suggest that PD-1+ HLA-DRHIGH KLRGLOW T cells are promising targets for prospective PD-1 antagonists and agonists in treating inflammatory diseases. This study not only reveals novel genes linked to PD-1 downstream functions but also serves as a valuable resource, offering insights for further investigations essential to delineate the role of PD-1 within immune responses.
Citation Format: Shoiab Bukhari, Shalom Lerrer, Johanna Straube, Robert Winchester, Brian Henick, Matthew Dragovich, Adam Mor. PD1 signaling uncovers a pathogenic subset of cytotoxic T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1367.