IL-15 Plus Thymosin α1 Reduces Senescent Hepatic CD8T Cells in Hepatocellular Carcinoma via PI3K/AKT Suppression.

BACKGROUND AND AIM: CD8T cell immunosenescence drives hepatocellular carcinoma (HCC) progression and impedes therapeutic efficacy. We hypothesized that combining interleukin-15 (IL-15), which rescues senescent CD8T cells peripherally, with thymosin alpha 1 (Tα1), which replenishes the T cell pool via thymic rejuvenation, may synergistically overcome immunosenescence and enhance antitumor immunity in HCC. METHODS: An orthotopic HCC model was established in aged C57BL/6 mice (22-26 months), randomly assigned to receive saline, IL-15, Tα1, or combined therapy. Tumor progression was monitored by bioluminescence imaging, survival analysis, and histopathology. Hepatic CD8T cell phenotype and function were evaluated by multicolor flow cytometry, immunofluorescence, transcriptomic sequencing, and Western blotting. In vitro validation used primary human CD8T cells co-cultured with Huh7 hepatoma cells. RESULTS: The combination therapy significantly suppressed tumor growth and prolonged survival. It reduced the proportion of senescent CD8T cells while expanding activated effector populations, enhanced proliferative capacity, and upregulated cytotoxic mediators including granzyme B, perforin, and interferon-gamma. Transcriptomic and protein-level analyses revealed that the combination attenuated chronically overactivated phosphatidylinositol 3-kinase/protein kinase B signaling in hepatic CD8T cells. A protein kinase B agonist, SC79, abrogated these therapeutic effects in vitro, confirming pathway suppression as the key mechanism. CONCLUSIONS: Combined IL-15 and Tα1 therapy reverses CD8T cell senescence and enhances antitumor immunity in HCC through suppression of the phosphatidylinositol 3-kinase/protein kinase B signaling pathway.