Zeaxanthin augments CD8+ effector T cell function and immunotherapy efficacy.

The detailed mechanisms underlying the regulatory significance of dietary components in modulating anti-tumor immunity remain largely unknown. Here, we apply a co-culture-based screening approach using a blood nutrient compound library and identify zeaxanthin (ZEA), a dietary carotenoid pigment found in many fruits and vegetables and known for its role in eye health, as an immunomodulator that enhances the cytotoxicity of CD8⁺ T cells against tumor cells. Oral supplementation with ZEA, but not its structural isomer lutein (LUT), enhances anti-tumor immunity in vivo. Integrated multi-omics mechanistic studies reveal that ZEA promotes T cell receptor (TCR) stimulation on the CD8⁺ T cell surface, leading to improved intracellular TCR signaling for effector T cell function. Hence, ZEA treatment augments the efficacy of anti-PD1 immune checkpoint inhibitor in vivo and the cytotoxicity of human TCR gene-engineered CD8⁺ T cells in vitro. Our findings uncover a previously unknown immunoregulatory function of ZEA, which has translational potential as a dietary element in bolstering immunotherapy.