Human CTLA4 Knockout Cell Line-Hela

Cytotoxic T lymphocyte antigen 4 (CTLA4) and programmed cell death protein 1 (PD-1) are immune checkpoint proteins expressed in T cells. Although CTLA4 is expressed in a variety of tumors, including non-small cell lung cancer (NSCLC) tissues and cells, its role in tumor cells is still unclear. Recently, studies have found that PD-1 is expressed in melanoma cells and promotes tumorigenesis. Researchers have found that CTLA4 is expressed in some NSCLC cell lines and a small group of cancer cells in lung cancer tissues. In NSCLC cells, anti-CTLA4 antibodies can induce PD-L1 expression, which is mediated by the CTLA4 and EGFR pathways, which involve phosphorylation of MEK and ERK. Anti-CTLA4 antibodies cannot induce PD-L1 expression in NSCLC cells in the presence of CTLA4 knockout cells, EGFR knockout cells, or EGFR tyrosine kinase inhibitors. In addition, anti-CTLA4 antibodies promote NSCLC cell proliferation in vitro and promote tumor growth in vivo in the absence of adaptive immunity. These results suggest that endogenous CTLA4 in tumor cells can regulate PD-L1 expression and cell proliferation, and that anti-CTLA4 antibodies may activate the EGFR pathway in cancer cells by binding to endogenous CTLA4 in tumor cells.

Based on the fact that anti-CTLA4 antibodies can activate the EGFR pathway in non-small cell lung cancer (NSCLC) cells, the researchers studied their effects on cell proliferation. A549 cells, A549 CTLA4 knockout cells, and A549 CTLA4 overexpression (OE) cells were tested using the MTT method. The researchers found that anti-CTLA4 antibody treatment promoted the proliferation of A549 cells (Figure 1A), and the proliferation effect was more significant in A549 CTLA4 OE cells, but not in A549 CTLA4 KO cells (Figure 1A). Next, the effects of anti-CTLA4 and anti-PD-1 treatment on the growth of xenograft tumors in nude mice were studied. Nude mice do not have T cells, so the function of tumor cell-intrinsic CTLA4 can be evaluated in the absence of adaptive immunity. The study found that anti-CTLA4 antibodies promoted the growth of xenograft tumors compared with control IgG treatment (Figure 1B). Anti-PD-1 antibodies inhibited the growth of xenograft tumors. The combined use of anti-CTLA4 and anti-PD-L1 antibodies can further inhibit tumor growth (Figure 1B). In the resected tumor tissue, anti-CTLA4 antibodies can increase the expression of PD-L1, while anti-PD-1 antibodies have no significant effect on the expression of PD-L1. The combined use of anti-CTLA4 and anti-PD-1 antibodies can increase the expression of PD-L1 in tumor tissue (Figure 1C).

Figure 1. Effects of anti-CTLA4 antibody on cell proliferation and tumour growth in the absence of adaptive immunity. (Zhang H, et al., 2019)