MAIT cell plasticity enables functional adaptation that drives antibacterial immune protection

Mucosal-associated invariant T (MAIT) cells are known for their rapid effector functions and antibacterial immune protection. Here, we define the plasticity of interferon-γ (IFN-γ)–producing MAIT1 and interleukin-17A (IL-17A)–producing MAIT17 cell subsets in vivo. Whereas T-bet + MAIT1 cells remained stable in all experimental settings, after adoptive transfer or acute Legionella or Francisella infection, RORγt + MAIT17 cells could undergo phenotypic and functional conversion into both RORγt + T-bet + MAIT1/17 and RORγt − T-bet + MAIT1 cells. This plasticity ensured that MAIT17 cells played a dominant role in generating antibacterial MAIT1 responses in mucosal tissues. Single-cell transcriptomics revealed that MAIT17-derived MAIT1 cells were distinct from canonical MAIT1 cells yet could migrate out of mucosal tissues to contribute to the global MAIT1 pool in subsequent systemic infections. Human IL-17A–secreting MAIT cells also showed similar functional plasticity. Our findings have broad implications for understanding the role of MAIT cells in combatting infections and their potential utility in MAIT cell–targeted vaccines.