MR1 and breast cancer: Since reactivity of our MR1-restricted TCR (10-59) to breast cancer cells was not inhibited by Ac-6-FP, but the response was significantly reduced by the K43A mutation of MR1, it is speculated that the antigenic molecule bound to MR1 more strongly than Ac-6-FP, and its binding was affected by the K43A mutation of MR1 molecules.