In lung cancer tissue and cell lines, C5a contributes to an immunosuppressive microenvironment by recruiting myeloid-derived suppressor cells and inducing the expression of several immunomodulators, including arginase 1 (ARG1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), IL-6, IL-10, lymphocyte-activation gene 3 (LAG3), and programmed cell death 1 ligand 1 (PD-L1 or CD274) (59). This evidence concerns the gene CTLA4 and lung cancer.