CTLA4 and lung cancer: Interestingly, Rui et al. reported that CTLA-4 expression increases when PBMCs are induced into CIK cells during in vitro culture, and inhibiting CTLA-4 expression by shCTLA-4 lentiviral particles can enhance CIK cells proliferation ex vivo and their cytotoxicity toward A549 lung cancer cell lines [20].