Targeting PHGDH reverses the immunosuppressive function in macrophages and enhances cancer immunotherapy

Phosphoglycerate dehydrogenase (PHGDH) has emerged as a crucial factor in facilitating macromolecule synthesis, neutralizing oxidative stress, and regulating methylation reactions in cancer cells, lymphocytes, and endothelial cells. However, the role of PHGDH in tumor-associated macrophages (TAMs) remains poorly understood. Here, we find that T helper 2 (Th2) cytokine interleukin-4 and the tumor-conditioned media increase the expression of PHGDH in macrophages and promote immunosuppressive M2 activation and proliferation. Loss of PHGDH disrupts cellular metabolism and mitochondrial respiration essential for immunosuppressive macrophages. Mechanistically, PHGDH-mediated serine biosynthesis promotes a-ketoglutarate production, which activates mTORC1 signaling and contributes to the maintenance of a M2-like macrophage phenotype in the tumor microenvironment. Genetically ablating PHGDH in macrophages of tumor-bearing mice results in attenuated tumor growth, reduced TAM infiltration, a phenotypic shift of M2-like TAMs towards an M1-like phenotype and enhanced anti-tumor T cell immunity. Our study provides a strong basis for further exploration of PHGDH as a potential target to counteract TAM-mediated immunosuppression and hinder tumor progression. Overall design: Gene expression profiling analysis of RNA-seq data obtained from Phgdhfl/fl Cx3cr1-Cre (macrophage-specific Phgdh deletion) bone marrow-derived macrophages (BMDMs) and Phgdhfl/fl BMDMs that were stimulated with AE17-tumor-conditioned medium for 24 hours. Each condition contains 4 biological replicates.