Abstract 6374: The role of myeloid cell-expressed PVRL2 in high-grade serous ovarian cancer

Abstract Ovarian cancer (OC) is the fifth leading cause of cancer death in women in the United States. Standard of care (surgical resection and platinum-based chemotherapy) has limited survival benefit for patients with advanced disease. Since 3 of every 4 patients are diagnosed with stage III-IV disease, novel therapeutic approaches are needed to improve survival. In trials with PD1/PD-L1 blockers, patients with OC had modest responses, highlighting an unmet need for effective immunotherapies. Our group has shown the PVRL2-PVRIG node in the DNAM-1 axis suppresses CD8 T cell effector function in syngeneic tumors as well as patient-derived ovarian tumors. This study aims to determine the requirement of tumor- vs myeloid cell-derived PVRL2 for driving immune suppression in OC. Taqman qPCR was conducted for PVRL2, PVR and PD-L1 mRNA expressions of classically activated (M1), and alternatively activated (M2) macrophages from wild-type and PVRL2−/− mice. In our syngeneic OC model, ID8-Vegf-Defb29 (50,000 cells/ovary) were surgically implanted in the ovarian bursa and monitored for disease progression. These studies were performed in (1) PVRL2−/− mice vs. wild type mice and (2) PVRL2−/− → Wild-type vs. wild-type → wild-type bone marrow chimeras. PVRL2−/- ID8-Vegf-Defb29 clones were generated by CRISPR-Cas9, validated for absence of off-target edits by whole exome sequencing and implanted in wild-type and PVRL2−/− mice. Multiplex immunofluorescence (mIF) of PanCK/CD8-CD68-PVRL2/PVR was performed on archived HGSOC tissue from patients treated at Johns Hopkins Hospital. CITE-seq was performed on viable TILs from 6 treatment-naïve and 4 neoadjuvant chemotherapy-treated patients. PVR transcripts were elevated in PVRL2−/− M1 (3.77-fold, p=0.04) and M2 (2.61-fold, p=0.003) macrophages compared to wild type. The expression of PD-L1 was increased in M2 macrophages of PVRL2-/- mice compared to wild-type mice (Mean ratio: 2.28, p=0.04). PVRL2−/− mice and PVRL2 bone marrow chimeras had significantly improved survival compared to their respective control cohorts. Tumors derived from PVRL2−/− ID8-Vegf-Defb29 clones grew slowly in PVRL2−/− mice compared to wild-type mice. PVRL2 and PVR were highly expressed in human HGSOC, and the prognosis was worse for patients with high PVRL2 expression. In mIF, PVRL2 was expressed not only on tumor cells but also on CD68-positive cells. In CITE-seq, PVRL2 and PVR were strongly expressed in macrophage and dendritic cell clusters. The enhanced expression of PVR and PD-L1 in PVRL2−/− M1 and M2 macrophages suggests compensatory activation of co-inhibitory signaling pathways. PVRL2 deficiency selectively in hematopoietically-reconstituted immune cells (primarily myeloid cells) and not in tumor cells conferred a significant survival benefit in our syngeneic OC model. Taken together, blockade of the PVRL2-PVRIG axis in conjunction with PD-1/L1 inhibition may be an effective modality in OC. Citation Format: Kosuke Murakami, Hirofumi Ando, Michele Doucet, William Huang, Sudipto Ganguly. The role of myeloid cell-expressed PVRL2 in high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6374.