Single-cell level studies have been conducted on HCC mucosa associated invariant T (MAIT) cells and found that MAIT cells were significantly enriched in the HCC microenvironment with upregulated expression of suppressor molecules such as PD-1, CTLA-4, and TIM-3, which correlated with poor clinical outcomes (Duan et al., 2019). Here, CTLA4 is linked to hepatocellular carcinoma.