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

Introduction/Rationale: The precise mechanisms linking TCR-dependent nutrient import and metabolic reprogramming to CD4+ T helper (Th) fate and function remain elusive. We recently demonstrated that the CBM complex facilitates TCR-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 nutrient transport, we employed siRNA-mediated knockdown and pharmacological inhibition of ASCT2/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: Targeted disruption of ASCT2 and GLUT1 reduced glutamine and glucose import respectively and decreased mTORC1 activity, including protein translation.
These defects were linked to MALT1 protease function and sustained by reduced nutrient import. Consequently, we observed reduced production of IFN and augmented secretion of Th2 (IL-4) and Tfh (IL-21) cytokines consistent with nutrient-dependent shifts in lineage-defining transcription factors, mirroring programs in CARD11 DN patient cells. Supplementing CARD11 DN T cells in vitro with glutamine and/or glucose yielded rebalanced differentiation towards a Th1 phenotype.

Conclusion: 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 represents a viable therapeutic avenue for treating patients with CARD11 DN mutations and other Th2-driven pathologies.