Abstract PO068: Distinct immune signatures predicting clinical response to PD-1 blockade therapy in gynecological cancers revealed by high-dimensional immune profiling

Although immune checkpoint blockade revolutionized cancer therapy, response rates have been mixed in gynecological malignancies. While uterine endometrial cancer with high microsatellite instability (MSI-HI) and high tumor mutational burden (TMB) respond robustly to checkpoint blockade, high-grade serous ovarian cancer (HGSOC) with low TMB respond modestly. Currently, there has been no known immune signature or T cell phenotype that predicts clinical response in gynecological tumors. To dissect the immune landscape and T cell phenotypes in gynecological cancer patients receiving PD-1 blockade, we used high-dimensional cytometry (flow cytometry and mass cytometry (CyTOF)). We performed longitudinal deep immune profiling of PBMC from patients with recurrent uterine endometrial cancer receiving single-arm nivolumab, and HSGOC patients receiving neoadjuvant nivolumab plus platinum-based chemotherapy prior to debulking surgery. Chemotherapy-resistant MSI-HI uterine cancer patients treated with nivolumab had a proliferative T cell response 2-4 weeks post PD-1 blockade, consistent with responses seen in high TMB melanoma and lung cancer. The responding Ki67+ CD8 T cell population was largely CD45RAloCD27hi or CD45RAloCD27lo and highly expressed PD1, CTLA-4, and CD39, consistent with the phenotype of exhausted T cells (TEX). These exhausted-like cells, especially expansion of T-bet+ subset, were enriched in responders, whereas early expansion of regulatory T cells (Treg) and enrichment of terminally differentiated effector/senescence-like T cells were observed in non-responders. Unlike patients with uterine endometrial cancer, patients with TMB-low ovarian cancer did not have a clear proliferative CD8 T cell response, but had an uncoupled proliferation of Treg, after neoadjuvant nivolumab plus chemotherapy treatment, suggesting systemic immune suppression in ovarian cancer patients. At baseline, ovarian cancer without recurrence had more terminally differentiated effector-like CD8 T cells, in contrast to TMB-high uterine cancer. Furthermore, in both cohorts, non-responders or patients with recurrence, had more naive-like cell population. Thus, both high and low TMB gynecological tumors have distinct immune landscapes associated with clinical response. Additionally, in MSI-HI uterine endometrial cancer patients, the length of time between the prior chemotherapy and the initiation of immunotherapy was negatively correlated with T cell reinvigoration and clinical response. This suggests that therapeutic timing and optimized strategies for combining chemotherapy and immunotherapy are still needed. Collectively, our immune profiling revealed the distinct immune signatures associated with clinical response to PD-1 blockade in gynecological cancers. Our results also suggest that high TMB (inflamed) versus low TMB (cold) tumor microenvironment, and timing of chemo/immunotherapy could impact differentiation and functions of T cells. Citation Format: Yuki Muroyama, Sasikanth Manne, Alexander C. Huang, Divij Mathew, Lakshmi Chilukuri, Allison R. Greenplate, Takuya Ohtani, Dmitriy Zamarin, Claire F. Friedman, E. John Wherry. Distinct immune signatures predicting clinical response to PD-1 blockade therapy in gynecological cancers revealed by high-dimensional immune profiling [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO068.