One-carbon Unit Supplementation Fuels Tumor-Infiltrating T Cells and Augments Checkpoint Blockade

Nucleotides perform important metabolic functions, carrying energy and feeding nucleic acid synthesis. Here, we use isotope tracing -mass spectrometry to quantitate contributions to purine nucleotides from salvage versus de novo synthesis. We further explore the impact of augmenting a key precursor for purine synthesis, one -carbon (1C) units. We show that tumors and tumor -infiltrating T cells (relative to splenic or lymph node T cells) synthesize purines de novo . Shortage of 1C units for T cell purine synthesis is accordingly a potential bottleneck for anti -tumor immunity. Supplementing 1C units by infusing formate drives formate assimilation into purines in tumor -infiltrating T cells. Orally administered methanol functions as a formate pro -drug, with deuteration enabling kinetic control of formate production. Safe doses of methanol raise formate levels and augment anti -PD -1 checkpoint blockade in MC38 tumors, tripling durable regressions. Thus, 1C deficiency can gate antitumor immunity and this metabolic checkpoint can be overcome with pharmacological 1C supplementation.