Ovarian cancer ascites induces a T cell suppressive phenotype in mature neutrophils: a potential barrier to anti-tumor immunity

Abstract

Abstract Ovarian cancer (OC) is often diagnosed at advanced stages and presents with ascites. Necrosis is a hallmark of advanced cancer and releases DAMPs that activate innate immune responses (e.g., neutrophils). While neutrophils are critical in host defense, their role in the context of tumor is less understood. CTLs correlate with better outcomes in advanced OC, and immunotherapy for cancer is based on augmentation of CTL responses. Our prior studies showed that granulocytes from ascites of patients with newly diagnosed OC suppressed donor T cell proliferation ex vivo. The current work probes mechanisms for this suppression. In ascites from patients with newly diagnosed OC, ~90% of cells were inflammatory (CD45+). Neutrophils comprised ~15% of CD45+ cells and the neutrophil:CD8+ T cell ratio was 1.5:1. In ex vivo studies, cell-free ascites (ASC; 500g) attracted normal donor neutrophils (NDN). While neither ASC nor NDN alone impaired CD3/CD28-stimulated normal donor T cell proliferation, ASC (10/15 patients) when combined with NDN (1:1) completely suppressed T cell proliferation. Suppression by ASC + NDN required cell contact and was lost if NDN were added after overnight CD3/CD28 stimulation of T cells. Finally, heat-inactivating ASC (56C, 1h) abrogated the ability of NDN to suppress T cell proliferation. Here we provide evidence that ascites recruits neutrophils to the tumor microenvironment and induces a suppressive phenotype of neutrophils that requires cell contact and heat-labile cell-free constituents. Ongoing studies aim to identify the putative protein(s) in ascites and the signaling effects on neutrophils. Our long-term goal is to develop novel approaches to overcome this suppression and improve durable anti-tumor immunity.