Mucosal-associated invariant T (MAIT) cells are innate-like T lymphocytes that recognize Vitamin B metabolites. Although MAIT cells provide rapid, innate-like responses, they are not pre-set and memory-like responses have been described. The importance of metabolism for controlling these responses, however, remains incompletely understood. Our previous findings indicated that different MAIT functions require distinct metabolic programs. Following antigen exposure, mouse MAIT cells expanded as antigen-adapted populations marked by CD127 and Klrg1. CD127+ MAIT17-like cells engaged in an energetic, mitochondrial metabolic program and active autophagy, which was critical for IL-17A synthesis. In contrast, Klrg1+ MAIT1 cells had dormant mitochondria and depended instead on Vhl-driven glycolysis for IFN-γ production.
Although human MAIT cells do not fit into MAIT1 and MAIT17 categories, their metabolism differed from conventional T cells by engaging a fatty acid fueled program that is evident in lung and blood at baseline. To study human MAIT cells following antigen adaptation (aaMAIT), we designed an updated protocol that relies on 5-OPRU presentation by antigen presenting cells and generates large numbers of aaMAIT cells. Lipid uptake and metabolism was further induced following exposure to antigen and expansion in vitro, correlating with TCR induced upregulation of Ki67 and Myc. Based on scRNA-seq, metabolomic and functional characterization, these human aaMAIT cells engaged functional and metabolic programs that depended on the nature of the activating trigger, either with the cytokines IL-12 and IL-18, TCR signals, or the combination. TCR signaling biased MAIT cells towards production of TNF and IL-17, and was associated with enhanced mitochondrial and lipid metabolic pathways. In contrast, cytokine-induced activation biased aaMAIT cells towards IFN-γ production associated with hypoxia-induced signaling. This suggests that the immunometabolic states of separate mouse MAIT1/17 subsets are reflected instead as activation-dependent bias in humans. Elucidating how metabolic programs integrate with functional responses of aaMAIT cells is critical for save clinical application of MAIT cells as adoptive cell immunotherapy.