Tissue resident memory T cells are enriched and dysfunctional in effusion of patients with malignant tumor

Purpose Most malignant effusion is secondary to metastases to the pleura or peritoneum and portend poor oncological outcomes. Malignant effusion has different tumor microenvironment from primary tumor, containing a variety of cytokines and immune cells and directly contacting with tumor cells. However, the characteristic of CD4⁺ T cells and CD8⁺ T cells in malignant effusion remains unclear. Methods Malignant effusion including peritoneal ascites and pleural fluid from thirty-five patients with malignant tumor were collected and compared with matched blood. A detailed characterization of CD4⁺ T cells and CD8⁺ T cells in malignant effusion were conducted using flow cytometry and multiple cytokines assay. Results The concentration of IL-6 in malignant effusion was significantly higher than in blood. A substantial portion of T cells in malignant effusion were CD69⁺ and/ or CD103⁺ Trm cells. Most CD4⁺T and CD8⁺T cells in malignant effusion were exhausted T cells which expressed lower levels of cytokines, cytotoxic molecules and markedly higher levels of inhibitory receptor PD-1 compared with in blood. Conclusion Our study is the first to identify the presence of Trm cells in malignant effusion and will lay the foundation for future research on anti-tumor immunity of Trm cells in malignant effusion.