Genistein enhances anti-PD-1 efficacy in melanoma by suppressing regulatory T cell differentiation and activity

The accumulation of regulatory T cells (Tregs) in the tumor microenvironment is a key factor for immunosuppression and immune escape of cancer cells. Genistein is a natural isoflavonoid in soybeans, possessing a wide range of pharmacological bioactivities. However, the immunomodulatory potential of genistein remains largely unexplored. This study investigated the synergistic efficacy of genistein with anti-PD-1 therapy in a mouse model of melanoma. The regulatory role of genistein in Treg differentiation and functional stability was also examined in this study. The antitumor effects of genistein, alone or in combination with anti-PD-1 therapy, were evaluated in the mouse B16-F10 melanoma model. The profiles of intratumoral Tregs and CD8⁺ cytotoxic T cells were profiled using flow cytometry. The impact of genistein on the suppressive function and differentiation of Tregs was also studied in vitro. RT-qPCR, Western blotting and flow cytometry were conducted to characterize the functional phenotype of Tregs under genistein treatment. Genistein showed a synergistic effect with anti-PD-1 therapy in B16-F10 melanoma models, achieving enhanced immune infiltration and functional reprogramming of the tumor microenvironment. This combinatorial strategy not only reduced intratumoral Tregs but also elevated the CD8⁺/Treg ratio. At the mechanistic level, genistein effectively suppressed critical Treg surface markers, which are indispensable for Treg-mediated immunosuppression. Furthermore, it disrupted Treg differentiation by attenuating PI3K/AKT signaling phosphorylation. Our data demonstrated that genistein boosts the antitumor effect of anti-PD-1 therapy by impairing the immunosuppressive function and differentiation of Tregs, indicating that genistein has the potential to enhance the treatment outcome of the immune checkpoint inhibitor.