Metabolic adaptations rewire CD4+ T cells in a subset-specific manner in human critical illness with and without sepsis.

Metabolic and immunologic dysfunction, including pathological CD4+ T cell immunosuppression, are archetypal in critical illness, but whether these factors are mechanistically linked remains incompletely defined. Here we characterized the metabolic properties of human CD4+ T cells from critically ill patients with and without sepsis and healthy adults. CD4+ T cells in critical illness showed subset-specific metabolic plasticity, with regulatory T (Treg) cells preferentially acquiring glycolytic capacity that associated with sustained cellular fitness and worsened clinical illness. Adapted Treg cells were more metabolically flexible and stabilized suppressive markers FOXP3 and TIGIT under mitochondrial stress. Single-cell transcriptomics suggested reactive oxygen species (ROS) and kynurenine metabolism as drivers of Treg cell remodeling. Subsequent inhibition of ROS and kynurenine metabolism attenuated glycolytic adaptation and suppressive rewiring, respectively, in Treg cells. These findings indicate that metabolic dysfunction was a contributor to CD4+ T cell remodeling in critical illness and suggest avenues to restore effective immunity.