NAD+ Supplement Potentiates Tumor Killing Function by Rescuing Defective Tubby-Mediated NAMPT Transcription in Tumor Infiltrated T Cells

An enigma of tumor immunology is that whereas maintaining capacities to proliferate, persist and eradicate tumors, tumor-infiltrating lymphocytes (TILs) are frequently dysfunctional in situ. By performing both whole-genome CRISPR and metabolic inhibitor screens, we identified that nicotinamide phosphoribosyltransferase (NAMPT) was required for T cell activation. Further studies showed that NAMPT was low in TILs, and its expression was dynamically controlled by the transcriptional factor Tubby (TUB), whose activity depends on the TCR-PLCgamma signaling axis. Consistently, the intracellular level of NAD+, whose synthesis is dependent on NAMPT-mediated salvage pathway, was also significantly decreased in TILs. LC-MS and isotopic labeling studies confirmed that NAD+ depletion in T cells led to suppressed glycolysis, disrupted mitochondrial function and dampened ATP synthesis. Excitingly, both adoptive CAR-T and anti-PD1 immune checkpoint blockade mouse models demonstrated that NAD+ supplementation enhanced the tumor-killing efficacy of T cells in vivo. In summary, this study revealed that impaired TCR-TUB-NAMPT-NAD+ signaling axis led to T cell dysfunction in tumor microenvironment, and an over-the-counter nutrient supplement of NAD+ could potentially boost the efficacy of T cell-based immunotherapy.