Resilient CD8⁺ T cells maintain a high cytotoxic capacity by balancing ROS and energy needs via ME1 upregulation

Abstract Cytotoxic T lymphocytes (CTL) are indispensable in anti-tumor immunity. Although CTLs are prone to exhaustion in patients with advanced cancer, T cell resiliency explains the presence of tumor-reactive CTLs that are less exhausted, capable of cytolytic function, expansion, and rebound in response to immunotherapy to reject metastatic malignancies. However, the features of resilient T cells have not been clearly defined. In this report, we demonstrate that peripheral CX3CR1 +CD8 +T cells with low mitochondrial membrane potential rebounded CTL function quickly after radiation therapy in patients with large tumor burden portraying their functional resiliency. Furthermore, CX3CR1 +CD8 +T cell with low, but not high, mitochondrial membrane potential are highly cytotoxic, accumulate less reactive oxygen species (ROS), and express more Malic enzyme 1 (ME1). ME1 overexpression increases ATP production in a glycolysis-independent manner while concurrently curtailing excessive ROS in activated CD8 +T cells; and expands CX3CR1 +NKG7 +effector CD8 +T cells with enhanced cytotoxicity. Importantly, transfection of ME1 mRNA promotes tumoricidal activity in CD8 +T cells from patients with advanced cancers. Our study reveals a mechanism used by CTLs to balance excessive ROS via ME1 to maintain a metabolic and functional resiliency. Modification of ME1 expression in CTLs may be a novel method to improve the efficacy of cancer immunotherapy by preventing T cell exhaustion. Supported by grants from Mayo Clinic Foundation and NIH (R01CA 256927-2)