While their role in cancer development and progression has not been fully elucidated, MAIT cells and specific populations of major histocompatibility complex class I-related (MR1)-restricted T-cells have been shown to infiltrate the tumor microenvironment and are able to lyse cancer cells in vitro and in vivo, indicating a potential role in cancer immunotherapy (2); Reviewed in Lukasik et al. (3). Here, MR1 is linked to cancer.