The CARD11–BCL10–MALT1 (CBM) Complex Regulates Nutrient Transport and mTORC1 Activation to Shape CD4+ T Cell Differentiation

Introduction The precise mechanisms linking TCR-dependent nutrient import and metabolic reprogramming to CD4+ T helper (Th) fate and function remain elusive. Here, we show that the CARD11–BCL10–MALT1 (CBM) complex facilitates activation-induced expression of the glutamine transporter ASCT2 and the glucose transporter GLUT1 on human CD4+ T cells. Notably, patient T cells carrying deleterious dominant-negative (DN) CARD11 mutations exhibit impaired activation-induced upregulation of both transporters, which we hypothesize contributes to the abnormal Th2 skewing and severe atopy observed in this cohort. Methods To test if observed phenotypes resulted from decreased CBM-dependent nutrient transport, we employed siRNA-mediated knockdown and pharmacological inhibition of CBM components, ASCT2 and GLUT1, in primary human T cells. Nutrient uptake and mTORC1 function were quantified in healthy and CARD11 DN samples using QUAS-R/2-NBDG import assays, flow cytometry, and immunoblotting. Th differentiation was assessed by spectral flow cytometry and high-sensitivity electrochemiluminescent immunoassays. Results We found that knockdown of any CBM component, or inhibition of MALT1 protease activity, markedly reduced TCR/CD28-dependent cell surface expression of ASCT2 and GLUT1, concomitant with impaired glutamine-dependent mTORC1 activation. While activation-induced ASCT2 transcription was repressed in CBM knockdown cells, GLUT1 upregulation was controlled by a CBM-dependent post-transcriptional mechanism. Similarly, ASCT2 and GLUT1 induction was significantly reduced in CARD11 DN patient T cells. Targeted disruption of ASCT2 and GLUT1 themselves reduced glutamine and glucose import, respectively, and decreased mTORC1 activity, including protein translation. Consequently, we observed reduced production of IFNy and augmented secretion of Th2 (IL-4) and Tfh (IL-21) cytokines. These results were consistent with nutrient-dependent shifts in lineage-defining transcription factors, mirroring programs observed in CARD11 DN patient cells. Supplementing CARD11 DN T cells in vitro with glutamine and/or glucose boosted mTORC1 activity and yielded rebalanced differentiation toward a Th1 phenotype. Conclusions Collectively, our results show that the CBM signalosome governs nutrient transport and mTORC1 activation to support Th1 differentiation of human T cells. Enhancing ASCT2/GLUT1 expression and/or nutrient import may represent a viable therapeutic strategy for treating patients with CARD11 DN mutations and other Th2-driven pathologies.