Abstract TMIM-063: TARGETING NEUROPILIN-1+ T REGULATORY CELLS IN PATIENTS WITH HIGH GRADE SEROUS OVARIAN CANCER DECREASES TREG-SPECIFIC SUPPRESSION OF CD8+ T CELLS

Abstract

Abstract Regulatory T cells (Treg) are a subpopulation of CD4+ T cells that suppress autoimmune responses, but also prevent clearance of tumors and chronic viral infections. In high grades serous ovarian cancer, a higher frequency of tumor infiltrating (TIL) Treg are associated with poor prognosis, but mechanisms governing the suppressive activity of TIL Treg in this context are limited. Our group has recently described a signaling axis through neuropilin-1 (NRP1) on TIL Treg in murine models of cancer that promotes the survival and suppressive function of Treg. When NRP1 is specifically knocked out on murine TIL Treg, there is reduced tumor growth and increased survival similar to the complete knockout of TIL Tregs, however, without death from overt autoimmunity. Thus, NRP1 is a viable target to specifically reduce TIL Treg suppressive function in the tumor microenvironment (TME), ultimately leading to increased anti-tumor immunity without adverse events. Given the importance of NRP1+ TIL Treg in murine cancer models, we sought to understand the role of NRP1 on TIL Treg from patients with high grade serious ovarian cancer. Surface and total NRP1 expression was assessed by flow cytometry on CD4+CD25+CD127loFOXP3+ Treg from healthy donor PBL and ovarian cancer TIL or ascites fluid. Total NRP1 was expressed on a median of 1.8% (interquartile range [IQR]: 0.69% to 4.8%) of Treg from healthy donors compared with a median of 66% (IQR: 28% to 90%; p<0.001) and 82% (IQR: 38% to 99%; p=0.004) of Treg from ovarian TIL and ascites, respectively. Surface NRP1 was detected on 0.1% (IQR: 0% to 1%) of Treg in PBL from healthy donors, compared with 11.1% (IQR: 1.1% to 60%; p=0.01) on ovarian TIL and 82% (IQR: 14% to 82%; p=0.0015) on ascites. Further, in comparing expression of NRP1 on Treg from benign ovarian disease and malignant ovarian tumors, there was a trend toward increased NRP1 expression on Tregs from malignant disease (median 9.3% versus 54.5%, respectively; p=0.044). Finally, NRP1+ TIL Treg isolated from primary tumors or ascites fluid were capable of suppressing CD8+ T cell proliferation in a dose-dependent manner and suppression was abrogated by addition of an anti-NRP1 antibody. In summary, both surface and total NRP1 are expressed more frequently on Treg from TIL and ascites fluid compared to Treg from healthy donor PBL and NRP1+ Tregs in the TME are more suppressive compared to NRP1- Tregs. NRP1 is a viable target to reduce Treg suppressive function in ovarian cancer tumors, which can be immunologically ““cold””. This could ultimately lead to increased CD8+ T cell infiltration and function in these patient tumors, which could then increase responsiveness to anti-PD1 as it relies upon CD8 T cell infiltration to be effective. Citation Format: Anthony R. Cillo, Christopher A. Chuckran, Mengting Liao, Francesmary Modugno, Robert Edwards, Lan Coffman, Dario A.A. Vignali, Tullia C. Bruno. TARGETING NEUROPILIN-1+ T REGULATORY CELLS IN PATIENTS WITH HIGH GRADE SEROUS OVARIAN CANCER DECREASES TREG-SPECIFIC SUPPRESSION OF CD8+ T CELLS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr TMIM-063.