Abstract

This study demonstrates that lactate promotes M2-like macrophage polarization by activating the TGF- β /SNAIL signaling axis, thereby weakening CD8 + T cell–mediated antitumor immunity and promoting breast cancer progression. In vitro experiments using bone marrow–derived macrophages (BMDMs) and THP-1 cells treated with 25 mM lactate revealed a marked increase in M2 markers (CD206, Arg-1, IL-10) and a reduction in M1 markers (iNOS, TNF- α , IL-12), confirmed by Western blotting and flow cytometry. RNA-Seq analysis identified TGF- β /SNAIL pathway activation, with increased TGFBR1/2 expression, Smad2/3 phosphorylation, and PI3K/AKT pathway enrichment. Functional studies revealed that lactate-polarized M2 macrophages impaired CD8 + T cell cytotoxicity (reduced IFN-γ, GzmB, PRF1; elevated PD-1, Tim-3) and disrupted mitochondrial metabolism. In vivo validation using a breast cancer xenograft model showed that lactate treatment increased tumor growth and angiogenesis (VEGF/CD31 + ), while TGF- β inhibition (SB431542) reversed these effects. Mechanistically, lactate-induced TGF- β /SNAIL signaling promoted EMT in cancer cells and created an immunosuppressive TME. These findings establish lactate as a critical metabolic regulator that coordinates macrophage polarization and T cell exhaustion through the TGF- β /SNAIL axis, highlighting this pathway as a promising therapeutic target for breast cancer immunotherapy. Graphical Schematic Representation of Lactate-Induced Breast Cancer Progression via the TGF- β /SNAIL Signaling Axis, Promoting M2 Polarization and Suppressing CD8⁺ T Cell Function (Created with BioRender).