Effect of intraperitoneal CF33-hNIS combined with PD-L1 blockade on gastric cancer peritoneal metastases and recurrence.

Abstract

433 Background: Peritoneal metastasis (PM) from gastric cancer (GC) carries a dismal prognosis and remains refractory to systemic therapies. Oncolytic virotherapy offers a novel peritoneal-targeted approach. We evaluated the efficacy of CF33-hNIS, a chimeric orthopoxvirus, alone and in combination with anti–PD-L1 immune checkpoint blockade in an immunocompetent mouse model of gastric cancer peritoneal metastasis (GCPM). Methods: A syngeneic GCPM model was established using ACKPY3944 murine GC cells. Mice received intraperitoneal (IP) CF33-hNIS alone or in combination with intravenous (IV) or IP anti–PD-L1. Tumor regression, survival, and immune responses were assessed. Flow cytometry and immunohistochemistry characterized CD3⁺ T-cell subsets in the peritoneal cavity and tumor microenvironment. Complete tumor regression (CTR) mice were rechallenged with ACKPY3944 cells to evaluate memory T-cell responses. Results: IP CF33-hNIS monotherapy significantly prolonged survival and increased CD3⁺ and CD8⁺ T-cell infiltration in both peritoneal fluid and tumor tissue. The most effective regimen—a single high-dose CF33-hNIS (10⁸ pfu) combined with IP anti–PD-L1 (Combo 2)—achieved 75% CTR. Mice with CTR rejected tumor rechallenge and exhibited marked expansion of effector and central memory T cells in the peritoneal cavity and spleen. Conclusions: IP CF33-hNIS exerts potent anti-tumor activity in GCPM, enhanced by concurrent IP anti–PD-L1. The high-dose Combo 2 strategy induces durable tumor-specific immunity and provides strong rationale for clinical translation of simplified, peritoneal-targeted oncolytic viro-immunotherapy in gastric cancer.