Lentiviral delivery of CTLA-4 shRNA improves the expansion of cytokine-induced killer cells and enhances cytotoxic activity in vitro

Cytokine-induced killer (CIK) cells are in vitro-expanded cells harboring potent toxicity against tumor cells. Recently, it was identified that the cytotoxicity and proliferation of CIK cells are restricted by a prolonged CIK cell culture period. Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) serves a negative role in T cell activation and proliferation. This study aims to determine whether CTLA-4 expression is associated with the inhibition of CIK cells. CIK cells were generated from peripheral blood mononuclear cells (PBMCs), and CTLA-4 shRNA (shCTLA-4) lentivirus was applied to knockdown CTLA-4 expression in CIK cells. The proliferation of CIK cells was evaluated following shCTLA-4 lentiviral transduction, and the cytotoxicity of CIK cells was investigated using the CytoTox 96 Non-Radioactive Cytotoxicity assay. The expression of CTLA-4 in CIK cells was significantly increased, compared with that in PBMCs. The shCTLA-4 lentivirus efficiently knocked down the expression of CTLA-4 in CIK cells. The shCTLA-4 lentivirus transduction of CIK cells promoted the proliferation of CIK cells in vitro (3.18±0.19-fold vs. 2.42±0.29-fold). Furthermore, the cytotoxicity of shCTLA-4 lentivirus-transduced CIK cells was significantly improved when compared with that of control shRNA lentivirus-transduced CIK cells (54.5±2.13% vs. 30.5±1.67%). Thus, the suppression of CTLA-4 expression increases cytotoxicity and ex vivo expansion of CIK cells, which indicates a clinical significance for CTLA-4 blockade in CIK cell therapy.