MicroRNA-124 Enhances T Cells Functions by Manipulating the Lactic Acid Metabolism of Tumor Cells

High production of lactic acid is a common feature of various tumors. Lactic acid is an immunosuppressive molecule with crucial roles in tumor cells' immune escape, which could largely be attributed to its negative effects on the T cells present in the tumor microenvironment (TME). Strategies that decrease the glycolysis rate of tumor cells could enhance immunosurveillance and limit tumor growth. Pyruvate kinase M2 (PKM2) is a key enzyme in the glycolysis pathway, and it plays a vital role in lactic acid buildup in the TME. MicroRNA (miR)-124 has been shown to be able to decrease tumor cell lactic acid synthesis indirectly by reducing PKM2 levels. In this study, we first overexpressed miR-124 in the tumor cells and evaluated its effects on the PKM2 expression and lactic acid production of the tumor cells using quantitative real-time polymerase chain reaction (qRT-PCR) and spectrophotometry, respectively. Then, we cocultured miR-124-treated tumor cells with T cells to investigate the effects of miR-124 overexpression on T cell proliferation, cytokine production, and apoptosis. Our results demonstrated that miR-124 overexpression could significantly reduce the amount of lactic acid produced by tumor cells by manipulating their glucose metabolism, which led to the augmented proliferation and IFN-γ production of T cells. Moreover, it rescued T cells from lactic acid-induced apoptosis. Our data suggest that lactic acid is a hindering factor for T-cell-based immunotherapies; however, manipulating tumor cells' metabolism via miR-124 could be a promising way to improve antitumor responses of T cells.