The development of MR1-restricted T (MR1T) cells is an exciting and promising area of research in the field of immunotherapy. Current T cell-based cancer immunotherapies are a patient-tailored treatment that can only be applied when HLA is matched and the target antigen is identified. On the other hand, MR1T cells appear to have a potential to be a safe and effective anti-cancer treatment without HLA-restriction. We identified TCRs from MR1T cells that can effectively recognize and kill various cancer cells without affecting normal cells. MR1T was produced by stimulating PBMCs from healthy donors and ovarian cancer patients with various cancer cell lines that were B2M-depleted and MR1-overexpressed. These MR1T cells showed strong anti-cancer activities against cancer cells of various tissue origins without cytotoxicity toward normal or virus-infected cells, regardless of HLA types. Paired αβ TCR sequences were analyzed at the single cell level in these MR1T cells, and the top 10 TCR clones were selected based upon the expression frequency. TCR signal report assay was performed to select TCR clones that respond to target cancer cells. Each candidate MR1 TCR clone was expressed on primary T cells using a lentiviral vector, and MR1T TCR clones showing strong anticancer efficacy were identified. Finally, we genetically modified part of the TCR sequence to improve the pairing of TCR α and β chains and increase their structural stability on T cells. Genetic modification of TCR sequences increased anticancer efficacy compared to the original TCR sequence.
In conclusion, we have identified MR1T TCR clones, which showed a strong anti-cancer activity to various types of cancers without affecting normal cells, regardless of their HLA types. These MR1T TCR clones can be developed into various types of effective and safe pan-cancer immunotherapeutics.