TMEM16F Phospholipid Scramblase Regulates Tumorigenesis by Modulating the Tumor Immune Microenvironment

The immunosuppressive tumor microenvironment enables immune evasion through mechanisms beyond canonical immune checkpoints. While phosphatidylserine (PS) externalization coordinates apoptotic clearance under physiological conditions, tumors exploit this pathway by mimicking apoptotic cells through PS exposure to suppress immune responses. Genetic ablation of TMEM16F abolished PS exposure, systemically reprogrammed the tumor microenvironment and primary immune organs toward immune activation, and suppressed tumor growth across cancer models. We performed single-cell RNA-seq (scRNA-seq) of tumor-infiltrating lymphocytes (TILs) from the TME of vector control or TMEM16F KO MC38 cells engrafted mice at 21 days. Total 10,782 single cells from MC38 colorectal tumor, colored by 14 cell types. The data demonstrated that the frequency of CD8+ T cell, NK cell, macrophage, myeloid-derived suppressor cell (MDSC), and Treg cell subsets were affected by TMEM16F deletion. Further analysis using flow cytometry and immunofluorescent staining confirmed the scRNA-seq findings, which indicated higher ratios of CD8+ T cells, NK cells, and M1 macrophages in the TMEs of TMEM16F KO mice.