Immunophenotype of Gastric Tumors Unveils a Pleiotropic Role of Regulatory T Cells in Tumor Development

SIMPLE SUMMARY: The role of regulatory T cells (Tregs) in gastric cancer (GC) is still controversial and poorly understood. GC patients have increased numbers of Tregs in peripheral blood and among tumor infiltrating lymphocytes; however, their prognostic value depends on specific tumor features (e.g., tumor location and/or microsatellite instability status). We found that Tregs might induce membrane expression of IL2Rα in intestinal-type GC cells, which associates with MAPK signaling pathway activation and spheroid growth. Moreover, Tregs accumulate at early steps of intestinal-type GCs progression, when tumors are starting to grow through the stomach wall, and do not present vascular and perineural invasion. Our findings suggest a novel non-immunosuppressive role of Treg cells in intestinal-type GC, which may unlock novel therapeutic immuno-oncology strategies for intestinal-type GC or other tumors with similar immune context. ABSTRACT: Gastric cancer (GC) patients display increased regulatory T cell (Tregs) numbers in peripheral blood and among tumor-infiltrating lymphocytes. Nevertheless, the role of Tregs in GC progression remains controversial. Here, we sought to explore the impact of Tregs in GCs with distinct histology, and whether Tregs can directly influence tumor cell behavior and GC development. We performed a comprehensive immunophenotyping of 82 human GC cases, through an integrated analysis of multispectral immunofluorescence detection of T cells markers and patient clinicopathological data. Moreover, we developed 3D in vitro co-cultures with Tregs and tumor cells that were followed by high-throughput and light-sheet imaging, and their biological features studied with conventional/imaging flow cytometry and Western blotting. We showed that Tregs located at the tumor nest were frequent in intestinal-type GCs but did not associate with increased levels of effector T cells. Our in vitro results suggested that Tregs preferentially infiltrated intestinal-type GC spheroids, induced the expression of IL2Rα and activation of MAPK signaling pathway in tumor cells, and promoted spheroid growth. Accumulation of Tregs in intestinal-type GCs was increased at early stages of the stomach wall invasion and in the absence of vascular and perineural invasion. In this study, we proposed a non-immunosuppressive mechanism through which Tregs might directly modulate GC cells and thereby promote tumor growth. Our findings hold insightful implications for therapeutic strategies targeting intestinal-type GCs and other tumors with similar immune context.