The invention relates to a method of isolating a T cell that expresses a T cell receptor capable of binding specifically to an antigen presented by a cancer cell in association with an MR1 molecule. The method comprises the steps of (a) providing a preparation of T cells, (b) contacting the preparation with cancer cells expressing MR1 protein； (c) isolating a T cell that is specifically reactive to said cancer cells.The invention further relates to a method of preparing a T cell preparation expressing select MR1 recognizing T cell receptors from transgene expression vectors, the use of such T cell preparations in treatment of cancer, and to collections of MR1 reactive T cell receptor encoding nucleic acids and cells.
