Redox sensor KEAP1 promotes stemness and prevents reductive stress in exhausted CD8+ T cells via inhibiting NRF2

Persistent antigen stimulation exposes CD8+ T cells to various metabolic stresses and induces a dysfunctional state termed T-cell exhaustion. Exhausted CD8+ T cells are continuously replenished by a recently discovered self-renewing stem-like CD8+ T-cell subset, which maintains long-term immunity and provides proliferative burst in response to immunotherapies. Although the redox system plays an important role in regulating T-cell activation, how cellular redox affects the differentiation of stem-like and exhausted CD8+ T cells is incompletely understood. Here, we showed that both antigen stimulation and terminal differentiation reduced mitochondrial oxidation and reactive oxygen species (ROS) in exhausted CD8+ T cells, which displayed a chromatin state primed for regulation by the redox sensing KEAP1-NRF2 pathway. During chronic viral infection, KEAP1 promoted expansion of antiviral CD8+ T cells and facilitated their differentiation into the stem-like subset in a cell autonomous manner. In addition, KEAP1 was required for establishing proper transcriptional programs of stem-like and exhausted CD8+ T cells. Mechanistically, KEAP1 maintained oxidation by upregulating genes involved in mitochondrial oxidation and repressing NRF2-driven transcription of antioxidant pathways. Deleting KEAP1 binding domain in NRF2 released NRF2 from regulation by KEAP1, impaired expansion and stemness of CD8+ T cells, and dysregulated multiple metabolic pathways including redox pathways. Thus, our study revealed a novel role of the redox pathway in regulating the molecular program and differentiation of stem-like and exhausted CD8+ T cells during chronic antigen stimulation.