Abstract 1761: Tissue Factor expression is associated with B7-H4-mediated immune evasion in ovarian clear cell carcinoma and with response to tisotumab vedotin in preclinical models

Abstract Objective: Ovarian clear cell carcinoma (OCCC) characteristically overexpresses Tissue Factor (TF; F3), yet its biological significance and therapeutic implications remain unclear. We aimed to elucidate the impact of TF expression in OCCC and evaluate the antitumor efficacy of the anti-TF antibody-drug conjugate, tisotumab vedotin (TV), in vitro and in vivo models. Methods: We performed bulk RNA sequencing (RNA-seq) of 112 clinical OCCC cases to identify transcriptomic features of F3-high tumors. We then applied single-nucleus RNA-seq (snRNA-seq) to three F3-high and three F3-low cases to characterize tumor biology at the single-cell level. Based on these transcriptomic results, we focused on immune-related pathways and immune-checkpoint molecules, with emphasis on VTCN1 (B7-H4). Immunohistochemistry for TF and B7-H4 was performed on 57 OCCC specimens. Finally, we assessed TV activity in patient-derived OCCC spheroids and xenografts. Results: F3-high tumors exhibited lower immune scores with upregulation of MYC and cell cycle pathways, and suppression of inflammatory and immune pathways in bulk RNA-seq. Consistently, snRNA-seq showed similar trends in cancer cells, and immune fractions were significantly reduced in F3-high tumors, indicating an immunologically “cold” state. Notably, the immune-checkpoint molecule VTCN1 was highly expressed in F3-high tumors and positively correlated with F3 expression. Immunohistochemistry confirmed that B7-H4 was significantly overexpressed in TF-positive tumors, showing a positive correlation between TF and B7-H4 expression.TV activity correlated with TF abundance in vitro and induced marked growth inhibition in F3-high xenografts; residual tumors showed decreased TF and B7-H4 expression. Conclusions: TF-high OCCC shows a distinct gene expression pattern, particularly an immunologically cold subtype with B7-H4-mediated immune evasion. TV demonstrates TF-dependent activity, supporting TF as a therapeutic target, and providing rationale for TV-based monotherapy or combinations with immunotherapy in OCCC. Citation Format: Yutaro Mori, Ryo Tamura, Kotaro Takahashi, Kosuke Yoshihara. Tissue Factor expression is associated with B7-H4-mediated immune evasion in ovarian clear cell carcinoma and with response to tisotumab vedotin in preclinical models [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 1761.