IL-2 rescues impaired T cell function upon loss of Itk via metabolic reprogramming

Abstract

Abstract IL-2 inducible T cell kinase (Itk) is a critical component of T cell receptor (TCR) signaling required for activation of PLCg and downstream transcription factors, that regulate expression of effector molecules. Loss of Itk impairs T-cell activation by modulating the strength of TCR signal. Itk −/−mice have defects in T cell development with decreased proliferation and impaired differentiation to multiple CD4 T helper lineages. Most severe defects are seen in differentiation of Th9 cells, which produce the cytokine, IL-9. Under Th9 differentiation conditions, Itk −/−cells initially appear similar to WT cells but at 72hrs fail to sustain long-term expression of effector molecules. Th9 differentiation could be rescued by inclusion of IL-2. Itk −/−CD4 T cells show decreased mTORC1 signaling and do not maintain expression of IRF4, c-Myc, pRb and multiple nutrient transporters, including the Glucose transporter 1 (GLUT1), transferrin receptor (CD71), and amino acid co-transporter (CD98), all of which were rescued by IL-2. IL-2 is not required initially but can be added as late as 48hrs into culture. Using SCENITH—a flow cytometry-based technique that profiles metabolism—we found that WT differentiated Th9 cells were primarily glycolytic. In contrast, Itk −/−Th9 cells were less synthetic and more dependent on mitochondrial respiration. Inclusion of IL-2 in Itk −/−cultures rescued metabolic profiles, comparable to WT cells. Our results suggest that metabolic flexibility is central to dictating the functional/effector fate of CD4 T cells and that the Tec kinase Itk and IL-2-mediated pathways are required for maintenance of metabolic integrity, providing novel insight into mechanisms by which IL-2 can rescue T cell functional defects. This work was supported by the Intramural Research Program of NIAID, NIH.