Despite the high tumor mutational burden (TMB), immune check point blockade (ICB) still fails in about half of microsatellite instability-high (MSI-H) cancer patients, suggesting underlying immune dysregulation. Immune profiling of peripheral blood from chemotherapy-resistant MSI-H uterine cancer patients treated with nivolumab identified a rapid proliferative CD8 T cell response 2-4 weeks post PD-1 blockade (N = 32). This immunological response, however, did not correlate with clinical response, suggesting additional parameters may be relevant. We focused on DNA damage and repair (DDR) in T cells as potential novel parameters. DDR has been extensively studied in the context of inducing cell death in highly-proliferating tumor cells. However, despite induction of rapid proliferation of T cells upon ICB, whether T cell-intrinsic DDR impacts T cell function, and how the coordination of DDR affects immunological and clinical response to ICBs have been largely unexplored. We hypothesized that the T celI-intrinsic DDR responses to proliferative and genotoxic stress might contribute to the disparity between immunological and clinical response. To test the hypothesis, we developed a novel high-dimensional cytometry platform. This DDR-Immune platform enables simultaneous analysis of T cell differentiation state with changes in major DDR pathways at single-cell resolution. The DDR-Immune platform revealed consistent T cell subset specific patterns of DDR, as well as specific DDR pathways induced by different types of DNA damage, such as γ-irradiation (IR), UV irradiation (UV) or proliferative stress (i.e. anti-CD3/CD28 stimulation). For example, terminally differentiated effector T cells accumulated higher DNA damage and cell death. In contrast, stem cell memory (TSCM) and regulatory T cells (Treg) displayed high DDR with less cell death, suggesting that effective cell-intrinsic DDR against genotoxic stress in T cells confers a survival advantage. We applied the platform to MSI-H uterine cancer cohort to test if T cell-intrinsic DDR distinguish the clinical response. Indeed, we found that in clinical responders but not clinical non-responders, Ki67+ CD8 T cells responding to PD-1 blockade exhibited rapid induction of DDR represented as a spike increase of phosphorylated-ATM (pATM). This likely indicates the T cell ‘fitness’ response to proliferative stress induced by PD-1 blockade. Furthermore, patients with higher induction of pATM in responding CD8 T cells at the peak of the immunological response to PD-1 blockade had longer progression-free survival (PFS). Collectively, the new platform reveals previously unrecognized roles for T cell-intrinsic DDR as a novel determinant of immune responsiveness and clinical outcome to ICB and has potential application to other cancer therapies including chemotherapy and radiotherapy.

Citation Format: Yuki Muroyama, Sasikanth Manne, Derek A. Oldridge, Nils Wellhausen, Allison R. Greenplate, Lakshmi Chilukuri, Divij Mathew, Caiyue Xu, Ramin S. Herati, Alexander C. Huang, Dmitriy Zamarin, Claire F. Friedman, E. John Wherry. T cell intrinsic DNA damage and repair response as a novel marker associated with clinical response to PD-1 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3579.