IL-15 Plus Thymosin α1 Reduces Senescent Hepatic CD8⁺ T Cells in Hepatocellular Carcinoma via PI3K/AKT Suppression

BACKGROUND AND AIM: CD8⁺ T cell immunosenescence drives hepatocellular carcinoma (HCC) progression and impedes therapeutic efficacy. We hypothesized that combining interleukin-15 (IL-15), which rescues senescent CD8⁺ T 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 CD8⁺ T cell phenotype and function were evaluated by multicolor flow cytometry, immunofluorescence, transcriptomic sequencing, and Western blotting. In vitro validation used primary human CD8⁺ T cells co-cultured with Huh7 hepatoma cells. RESULTS: The combination therapy significantly suppressed tumor growth and prolonged survival. It reduced the proportion of senescent CD8⁺ T 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 CD8⁺ T 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 CD8⁺ T cell senescence and enhances antitumor immunity in HCC through suppression of the phosphatidylinositol 3-kinase/protein kinase B signaling pathway.