Shi et al. (2017) and Zhang et al. (2019) knocked out CTLA-4 in cytotoxic T lymphocytes (CTLs) using CRISPR/Cas9 system, and found that CTLA-4 disruption, as compared with control groups, could increase TNF-α and IFN-γ secretion and enhance anti-tumor activity of CTLs. This evidence concerns the gene CTLA4 and neoplasm.