Folate metabolism in tumor-associated macrophages drives immunosuppressive function to promote tumor growth
- 1University of North Carolina at Chapel Hill
Abstract
Tumor-associated macrophages (TAMs) promote tumor growth, inhibit effector lymphocytes, and induce resistance to immune checkpoint inhibitors (ICI). Therapies designed to deplete TAMs have had little success in the clinic, and strategies aimed to repolarize immunosuppressive TAMs to pro-inflammatory states have struggled with systemic toxicity. We have identified that the combination of low folate in the tumor microenvironment and TAM dependency on the high affinity folate receptor beta (FR{beta}) for folate uptake results in a unique metabolic dependency of TAMs necessary for their immunosuppressive function. FR{beta} (encoded by Folr2) is uniquely expressed on myeloid cells and upregulated on TAMs. FR{beta}+ TAMs exhibit an immunosuppressive phenotype in melanoma and are associated with worse clinical outcomes and resistance to ICI in melanoma patients. We generated a novel Folr2-/- mouse model to study why TAMs express a unique folate receptor and showed that tumor growth was slowed in the absence of Folr2 in a T-cell dependent manner. We observed a dramatic repolarization of Folr2-/- TAMs in vivo to pro-inflammatory states, resulting in increased cytotoxic T cell and NK cell infiltration into tumors. Importantly, we show that folate is low in the tumor microenvironment by performing metabolomics on melanoma tumors and adjacent normal tissue from warm autopsy patient specimens, and that we could increase tumor growth in Folr2-/- mice by increasing serum folate to supraphysiologic concentrations with a high folate diet. Integrated metabolomics and transcriptomic analysis demonstrated that Folr2-/- macrophages have impaired folate uptake and 1C metabolism-based reduction of oxidized glutathione in low folate conditions, resulting in increased mitochondrial reactive oxygen species (ROS) in Folr2-/- cells. Excess ROS results in leakage of mitochondrial DNA into the cytoplasm, activating cGAS-STING signaling and promoting pro-inflammatory macrophage polarization through TBK1 and NF-kB. Together, our data demonstrate that TAM expression of FR{beta} promotes their immunosuppressive functions by maintaining folate uptake in the low folate tumor microenvironment, suggesting that FR{beta} is a novel metabolic checkpoint on TAMs.
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BibTeX
@misc{zimmerman2026folate,
title = {{Folate metabolism in tumor-associated macrophages drives immunosuppressive function to promote tumor growth}},
author = {M. P. Zimmerman and V. Zhabotynsky and H. Wang and E. K. Cox and W. L. Chong and A. G. Bastian and A. S. Kennedy and B. P. Fay and A. G. Reynolds and A. Ebacher and J. A. Meier and K. Vietor and K. E. Taylor and P. C. Onuoha and S. Maruvada and K. E. Hurst and C. Wong and C. W. Anderson and N. E. Thomas and R. Liu and K. L. Bryant and A. S. Baldwin and D. W. Ollila and J. P.-Y. Ting and B. R. Rushing and S. J. Sumner and S. A. Krupenko and W. HUGO and S. J. Moschos and J. E. Thaxton and B. C. Miller},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.29.755523},
url = {https://www.biorxiv.org/content/10.64898/2026.09.29.755523v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Folate metabolism in tumor-associated macrophages drives immunosuppressive function to promote tumor growth
AU - M. P. Zimmerman
AU - V. Zhabotynsky
AU - H. Wang
AU - E. K. Cox
AU - W. L. Chong
AU - A. G. Bastian
AU - A. S. Kennedy
AU - B. P. Fay
AU - A. G. Reynolds
AU - A. Ebacher
AU - J. A. Meier
AU - K. Vietor
AU - K. E. Taylor
AU - P. C. Onuoha
AU - S. Maruvada
AU - K. E. Hurst
AU - C. Wong
AU - C. W. Anderson
AU - N. E. Thomas
AU - R. Liu
AU - K. L. Bryant
AU - A. S. Baldwin
AU - D. W. Ollila
AU - J. P.-Y. Ting
AU - B. R. Rushing
AU - S. J. Sumner
AU - S. A. Krupenko
AU - W. HUGO
AU - S. J. Moschos
AU - J. E. Thaxton
AU - B. C. Miller
PY - 2026
DA - 2026/09/29
PB - bioRxiv
DO - 10.64898/2026.09.29.755523
UR - https://www.biorxiv.org/content/10.64898/2026.09.29.755523v1
AB - Tumor-associated macrophages (TAMs) promote tumor growth, inhibit effector lymphocytes, and induce resistance to immune checkpoint inhibitors (ICI). Therapies designed to deplete TAMs have had little success in the clinic, and strategies aimed to repolarize immunosuppressive TAMs to pro-inflammatory states have struggled with systemic toxicity. We have identified that the combination of low folate in the tumor microenvironment and TAM dependency on the high affinity folate receptor beta (FR{beta}) for folate uptake results in a unique metabolic dependency of TAMs necessary for their immunosuppressive function. FR{beta} (encoded by Folr2) is uniquely expressed on myeloid cells and upregulated on TAMs. FR{beta}+ TAMs exhibit an immunosuppressive phenotype in melanoma and are associated with worse clinical outcomes and resistance to ICI in melanoma patients. We generated a novel Folr2-/- mouse model to study why TAMs express a unique folate receptor and showed that tumor growth was slowed in the absence of Folr2 in a T-cell dependent manner. We observed a dramatic repolarization of Folr2-/- TAMs in vivo to pro-inflammatory states, resulting in increased cytotoxic T cell and NK cell infiltration into tumors. Importantly, we show that folate is low in the tumor microenvironment by performing metabolomics on melanoma tumors and adjacent normal tissue from warm autopsy patient specimens, and that we could increase tumor growth in Folr2-/- mice by increasing serum folate to supraphysiologic concentrations with a high folate diet. Integrated metabolomics and transcriptomic analysis demonstrated that Folr2-/- macrophages have impaired folate uptake and 1C metabolism-based reduction of oxidized glutathione in low folate conditions, resulting in increased mitochondrial reactive oxygen species (ROS) in Folr2-/- cells. Excess ROS results in leakage of mitochondrial DNA into the cytoplasm, activating cGAS-STING signaling and promoting pro-inflammatory macrophage polarization through TBK1 and NF-kB. Together, our data demonstrate that TAM expression of FR{beta} promotes their immunosuppressive functions by maintaining folate uptake in the low folate tumor microenvironment, suggesting that FR{beta} is a novel metabolic checkpoint on TAMs.
ER -