Pathogenic mechanisms underlying the development of lung cancer are very complex and not yet entirely clarified. T lymphocytes and their immune-regulatory cytokines play a pivotal role in controlling tumor growth and metastasis. Following activation by unique cytokines, CD4+ T helper cells differentiate into Th1, Th2, Th17, and regulatory T cells (Tregs). Traditionally, research in lung cancer immunity has focused almost exclusively on Th1/Th2 cell balance. Recently, Th17 cells and Tregs represent an intriguing issue to be addressed in lung cancer pathogenesis. Tregs play an important role in the preservation of self-tolerance and modulation of overall immune responses against tumor cells. Th17 cells directly or via other proinflammatory cytokines modulate antitumor immune responses. Notably, there is a close relation between Tregs and Th17 cells. However, the possible interaction between these subsets in lung cancer remains to be elucidated. In this setting, targeting Treg/Th17 balance for therapeutic purposes may represent a useful tool for lung cancer treatment in the future. The purpose of this review is to discuss recent findings of the role of these novel populations in lung cancer immunity and to highlight the pleiotropic effects of these subsets on the development and regulation of lung cancer.

Chronic obstructive pulmonary disease (COPD) is a progressive and irreversible chronic inflammatory disease associated with the accumulation of activated T cells. To date, there is little information concerning the intrinsic association among Th17, Tc17, and regulatory T (Treg) cells in COPD. The objective of this study was to investigate the variation of lungs CD4(+)Foxp3(+) Treg cells and IL-17-producing CD4 and CD8 (Th17 and Tc17) lymphocytes in mice with cigarette-induced emphysema. Groups of mice were exposed to cigarette smoke or room air. At weeks 12 and 24, mice were sacrificed to observe histological changes by HE stain. The frequencies of Th17 (CD4(+)IL-17(+)T), Tc17 (CD8(+)IL-17(+)T), and Treg (CD4(+)Foxp3(+)T) cells in lungs from these mice were analyzed by flow cytometry. The mRNA levels of orphan nuclear receptor ROR γt and Foxp3 were performed by real-time quantitative polymerase chain reaction. The protein levels of interleukin-17 (IL-17), IL-6, IL-10, and transforming growth factor-beta (TGF-β1) were measured by enzyme-linked immunosorbent assay. Cigarette smoke caused substantial enlargement of the air spaces accompanied by the destruction of the normal alveolar architecture and led to emphysema. The frequencies of Th17 and Tc17 cells, as well as the expressions of IL-6, IL-17, TGF-β1, and ROR γt were greater in the lungs of cigarette smoke (CS)-exposed mice, particularly in the 24-week CS-exposed mice. The frequencies of Treg cells and the expressions of IL-10 and Foxp3 were lower in CS-exposed mice compared to control group. More important, the frequencies of Tregs were negatively correlated with Th17 cells and with Tc17 cells. Interestingly, a significant portion of the cells that infiltrate the lungs was skewed towards a Tc17 phenotype. Our findings suggest the contribution of Th17, Tc17, and Treg cells in the pathogenesis of COPD. Rebalance of these cells will be helpful for developing and refining the new immunological therapies for COPD.

The fine balance of T help-17 (Th17)/regulatory T(Treg) cells is crucial for maintenance of immune homeostasis. However, there is little information concerning the role played in non-small cell lung cancer (NSCLC) by Th17/Treg cells. The objective of this study was to investigate the variation of Th17 and Treg cells in the peripheral blood of patients with NSCLC. Blood samples were collected from 19 patients with NSCLC and 19 healthy donors. Samples were processed to detect CD4(+)IL-17(+) Th17 cells and CD4(+)CD25(+)Foxp3(+) Treg cells by flow cytometry, and related gene expressions were assessed by real-time quantitative polymerase chain reaction. The concentrations of interleukin (IL)-1β, IL-6, IL-10, IL-17, IL-23, and transforming growth factor-beta (TGF-β1) were also measured by enzyme-linked immunosorbent assay analysis (ELISA). The frequency of circulating Th17 cells and Treg cells was increased in samples derived from patients with NSCLC, accompanied by the upregulation of Foxp3 and RORγt. However, a negative correlation between Treg cells and Th17 cells was found in patients with NSCLC. Additionally, the Th17/Treg ratio and the related cytokines were also significantly higher in patients with NSCLC than in healthy controls. Furthermore, the frequency of Th17 cells was positively correlated with IL-1β, IL-6, and IL-23 in patients with NSCLC, and the frequency of Treg cells was positively correlated with TGF-β1 and IL-10. More importantly, the Th17/Treg ratio was positively correlated with the CEA concentrations in patients with NSCLC. Our data indicated that Th17 and Treg subset are involved in the immunopathology of NSCLC. Distinct cytokine environment might play a key role in the differentiation of the Th17 and Treg cells in NSCLC. Reconstituting an adequate balance between Th17 and Treg may be beneficial in the treatment of NSCLC.