Perhaps, Vitamin B2,if it works.
The idea is supply enough riboflavin so gut bacteria wont try and make their own.
MAIT cells are activated when they sense precursers to B vitamins.
lots of old info on site search b2 oldmike but not sure I covered this aspect,other than
MAIT activation but not how to inhibit.
Why would you want to shut down MAIT cells.There is a lot more out there if you search.https://pubmed.ncbi.nlm.nih.gov/28442662/