Intraperitoneal CF33-hNIS combined with PD-L1 blockade eradicates gastric cancer peritoneal metastases and prevents recurrence via durable T cell memory.

Abstract

BACKGROUND: Peritoneal metastasis (PM) from gastric cancer (GC) is associated with poor prognosis and limited treatment options. We investigated a novel peritoneal-targeted therapy using CF33-human sodium iodide symporter (hNIS), a chimeric orthopoxvirus, combined with anti-PD-L1 immune checkpoint blockade in an immunocompetent mouse model of GCPM. METHODS: We evaluated replication and cytotoxicity of CF33-hNIS in human and murine GC cell lines. We assessed a syngeneic mouse model of PM using the transgenic mouse GC ACKPY3944 cells to test the efficacy of intraperitoneal (IP) CF33-hNIS alone and combined with intravenous or IP anti-PD-L1. Next, we performed flow cytometry and immunohistochemistry to analyze immune cell populations of CD3T cell subsets in the peritoneal cavity and tumor microenvironment. Mice that showed complete tumor regression (CTR) were rechallenged with ACKPY3944 cells to assess memory T cell responses. RESULTS: CF33-hNIS efficiently infected and killed GC cells. In vivo, IP CF33-hNIS alone significantly prolonged survival and increased infiltration of CD3and CD8T cells within the peritoneal cavity and solid tumor. The most pronounced therapeutic effect was observed with a single high-dose of CF33-hNIS (10plaque-forming units) combined with IP anti-PD-L1 (Combo 2) with 75% CTR. Notably, mice with CTR rejected tumor rechallenge, exhibiting significantly elevated effector and central memory T cell populations in the peritoneal cavity and spleen. IP CF33-hNIS demonstrates robust anti-tumor efficacy against GCPM, particularly when combined with IP anti-PD-L1 in the high-dose Combo 2 regimen. CONCLUSIONS: These findings support a simplified, high-dose IP treatment strategy to overcome immune resistance in GCPM and provide a strong rationale for future clinical evaluation.