T cell trafficking within the peritoneal tumor environment and ovarian cancer progression.

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5573 Background: Ovarian cancer is associated with high mortality due to detection at late stages with widespread peritoneal metastases at diagnosis in a majority of patients. Ovarian cancer recurrences are primarily found in the peritoneal cavity, and peritoneal disease is the primary cause of morbidity and mortality in this disease. This pattern of tumor engraftment and recurrence indicates that the peritoneal tumor environment is distinct from other niches. Our data indicate that selective peritoneal dissemination is immunologically mediated, based on functional differences in peritoneal and systemic T cells during ovarian cancer progression. This is consistent with data in other solid tumors demonstrating that tumor immunity is driven by regional lymphocyte populations. However, less is known about the mechanisms that establish a permissive immune environment in the peritoneal cavity. We hypothesize that pathways regulating T cell recruitment and retention in the peritoneal cavity (PC) are co-opted by ovarian cancer cells to enable intraperitoneal cancer dissemination and recurrence. Methods: We have developed a novel model that uses direct in vivo labeling of peritoneal cells in an established immune-competent high grade serous murine cancer model. This functional approach enables us to identify T cell subsets retained in the PC with tumor engraftment and progression. Results: We identified high expression of CD49d (a4 integrin) as the most prevalent cell surface marker on T cells retained in the peritoneal cavity, consistent with prior published data in healthy mice and people. We demonstrated a functional role for CD49dhi in T cell retention by showing preferential binding to VCAM. A role for tumor cells mediating this interaction was observed based on enhanced binding affinity in vitro with tumor monolayers. The importance of this mechanism is supported by high VCAM expression in multiple murine and human ovarian cancer cell lines, and T cell localization to VCAM rich areas within ovarian cancer tumors in vivo. Conclusions: CD49d not only defines a lymphocyte subset with a significant role in tumor immunity but presents itself as an important potential therapeutic target to modulate T cell trafficking.