Tumor-Specific Cytotoxic T Cells Are Crucial for Efficacy of Immunomodulatory Antibodies in Patients with Lung Cancer

There is growing evidence that activation of the immune system may be an effective treatment for patients with either small cell lung cancer or non-small cell lung cancer (NSCLC). Immunomodulatory antibodies directed against cytotoxic T cell-associated antigen 4 (CTLA-4/CD152) and programmed cell death ligand 1 (PDL1/CD274) showed clinical efficacy in patients with lung cancer. The key immune cells responsible for antitumor activity are the CTLs. The presence of these tumor-directed CTLs, both in number and functionality, is a prerequisite for the immune system to attack cancer cells. Immunomodulatory agents attempt to increase the efficacy of CTL activity. Thus, the limited number of patients who benefit from immunomodulatory antibodies may be caused by either an inadequate number or the impairment of CTL activity by the hostile environment created by the tumor. In this review, we discuss tumor-induced impairment of CTLs and experimental treatments that can stimulate T-cell responses and optimize specific CTL function. We discuss 2 types of immune cells with known suppressive capacity on CTLs that are of pivotal importance in patients with lung cancer: regulatory T cells and myeloid-derived suppressor cells.