Abstract 4303: Reprogramming tumor immunogenicity by targeting EGFL6 in ovarian cancer

Abstract Ovarian cancer remains the most lethal gynecologic malignancy, and current therapeutic options beyond surgery and chemotherapy provide only modest benefit. Although immune checkpoint inhibitors (ICIs) have transformed treatment for several cancer types, their efficacy in ovarian cancer is limited, partly due to downregulation of Major Histocompatibility Complex class I (MHC-I) that impairs antigen presentation and CD8+ T cell-mediated tumor control. Emerging evidence suggests that epidermal growth factor-like protein 6 (EGFL6), produced by cancer-associated fibroblasts and malignant epithelial cells, promotes tumor progression and immune evasion; however, its role in tumor immunogenicity remains unclear. To address this gap, we quantified surface MHC-I by flow cytometry following EGFL6 knockdown using lentiviral shRNA, with efficiency validated by western blotting. Protein abundance and signaling changes were assessed by SDS-PAGE and immunoblotting. Functional consequences were evaluated in co-culture assays with activated OT-I CD8+ T cells to measure cytotoxicity and cytokine production. We found that EGFL6 expression inversely correlates with immune infiltration in human ovarian tumors, with EGFL6-high tumors exhibiting a 30-50% reduction in CD8+ T-cell density. Therapeutic blockade of EGFL6 using a monoclonal antibody significantly enhanced antitumor immunity in ID8 and KPCA ovarian cancer models in C57BL/6 mice, increasing intratumoral CD8+ T-cell infiltration by ∼1.5-fold and elevating granzyme B+ and IFN-γ+ CD8+ T-cell frequencies. Mechanistically, EGFL6 promoted internalization and lysosomal degradation of surface MHC-I, reducing H-2Kb/H-2Db or HLA-A/B/C expression by 40-60% in mouse and human ovarian cancer cells. EGFL6 knockdown or antibody blockade restored MHC-I stability, resulting in a ∼2-fold increase in surface MHC-I and improved CD8+ T cell-mediated tumor recognition. These findings identify EGFL6 as a previously unrecognized regulator of tumor immunogenicity and provide strong preclinical rationale for combining EGFL6 inhibition with immunotherapeutic strategies in ovarian cancer. Citation Format: Weiche Wu, Zonghao Tang, Sujanitha Umamaheswaran, Zhiqiang An, Ningyan Zhang, Lingegowda S. Mangala, Anil K. Sood. Reprogramming tumor immunogenicity by targeting EGFL6 in ovarian cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4303.