MAIT cells as attractive vaccine targets.

Mucosal-associated invariant T (MAIT) cells are a subset of T cells that perform innate-like immunity functions upon recognition of small molecule vitamin B metabolites presented by the MHC, class I-related protein-1 (MR1). MAIT cells are profuse in humans, but especially abundant in blood, liver, lungs, and mucosal layers. The mucosa is a common site of carcinogenesis and MAIT cells have been found in both primary and metastatic tumors. MAIT cells target a host of microbes including Mycobacterium tuberculosis, Staphylococcus aureus, Salmonella enterica, Legionella longbeachae, Escherichia coli, and Candida albicans, and are highly activated in viral infections. Cytokines produced by MAIT cells are both anticancerous and antibacterial, but also have proinflammatory and possibly tumorigenic properties. In addition, it is believed that MAIT cells play a protective role in viral infections in an MR1-independent fashion. Based on our summary of recent advances concerning both MR1-mediated and MR1-independent MAIT cell immune responses, we weigh the strengths and weaknesses of these cells for vaccine development.