Dissecting the Glycolytic Requirements of Human T cells via G6PC3 Deficiency

Glucose metabolism is thought to play a pivotal role in proper activation and differentiation of T cells and in sustaining T cell effector functions. However, the glycolytic requirements of T cells in vivo in humans remain elusive, in part, due to the impossibility of prolonged inhibition of glycolysis. We tackle this limitation by studying glucose-6-phosphatase catalytic subunit 3 (G6PC3) deficiency, which is a rare immunometabolic disorder that causes intracellular accumulation of the metabolite 1,5-anhydroglucitol-6-phosphate (1,5-AG6P) in immune cells. This accumulation is known to prompt cell death in neutrophils by inhibiting glycolysis. However, neutrophil-independent clinical phenotypes have been reported in some G6PC3-deficient patients, suggesting a broader immunodeficiency. When treated with 1,5-anhydroglucitol (1,5-AG), the precursor to 1,5-AG6P, prior to extracellular flux assays, G6PC3 CRISPR/Cas9 knockout Jurkat T cells exhibited impaired glycolytic activities. This finding indicates that the 1,5-AG6P accumulation resulting from G6PC3 deficiency alters T cell metabolism. We then performed Single-Cell ENergetIc metabolism by profiling Translation inHibition (SCENITH) analysis on primary T cells from G6PC3-deficient patients, and we confirmed that patient T cells have markedly reduced glycolytic capacity when compared with cells from healthy donors. This metabolic defect is particularly noticeable in CD4+ and CD8+ effector memory T cells. Moreover, in-depth immunophenotyping by cytometry by time of flight (CyTOF) showed that G6PC3-deficient patients display lower frequencies of naïve T cells with a concomitant increase in the effector memory T cell and TEMRA proportions in both CD4+ and CD8+ compartments. Within the CD4+ T cells, patients also have an increased frequency of TH2/TH17 (CD4+CD45RA-CXCR3-) cells and indications of impaired thymic function. Furthermore, our data reveal that memory T cells from G6PC3-deficient patients exhibited elevated PD-1 expression. CD3/CD28 stimulation induces a significantly greater upregulation of PD-1 expression in CD4+ and CD8+ T cells from patients than those from healthy donors. An integrative analysis of scRNA-seq and scTCR-seq data shed light on the potential mechanisms underlying these observations. Collectively, these findings demonstrate that T cells from G6PC3-deficient patients reflect how impaired glycolysis profoundly impacts human T cell activation, differentiation, and function in previously unrecognized ways.