Astragalus polysaccharide promotes CD8 + T cell activity by downregulating Tim-3 to potentiate antitumor immunity.

It is well known that Astragalus polysaccharide (APS) exerts potent antitumor effects by enhancing T cell cytotoxicity via the PD-1/PD-L1 axis. However, whether APS can also modulate T cell activity via alternative checkpoint molecules remains unclear. Here, we addressed this question using complementary in vitro and in vivo approaches. In vitro, APS reduced the Tim-3 + cell population among human PBMCs. Further analysis revealed that APS specifically affected only the proportion of Tim-3 +CD8 + T cells. Along with the decreased proportion of Tim-3 + cells, CD8 + T cell immune activity was enhanced, as shown by increased expression of the early activation molecule CD69, increased secretion of GZMB, and enhanced capacity to kill human lung cancer cells. The results of transcriptome sequencing suggested that the APS-induced downregulation of Tim-3 might be related to the regulation of the transcription factor RORB. Experiments in an in vivo B16-F10 melanoma model revealed that APS enhanced T cell function by reducing the number of tumor-infiltrating Tim-3 + T cells, consequently suppressing tumor cell proliferation in mice. Collectively, our findings demonstrate that APS reduces the Tim-3 +CD8 + T cell population among PBMCs and enhances T cell cytotoxicity, providing a novel theoretical foundation for explaining the mechanism underlying APS immunomodulation.