Expression of Foxp3 in non-small cell lung cancer patients is significantly higher in tumor tissues than in normal tissues, especially in tumors smaller than 30 mm.

Active suppression by CD4+CD25+ T regulatory cells (T regs) plays an important role in the down-regulation of T cell responses to foreign and self-antigens. Thus far, the potential role of T regs in human tumors has been reported. T reg-mediated suppression of antitumor immune responses may partly explain the poor clinical response to vaccine-based immunotherapy for human cancer. The forkhead transcription factor Foxp3 is a critical regulator of T regs development and function. Foxp3 represents a specific marker for the T regs. In this study, we measured the Foxp3 mRNA expression in tumors and in normal tissues from 46 patients with non-small cell lung carcinoma (NSCLC), and tumor tissues showed a significantly higher expression of Foxp3 mRNA than normal tissues. The expression of Foxp3 mRNA and the tumor diameter were inversely proportional. These results suggest that T regs expressing Foxp3 selectively accumulate in tumor tissues of NSCLC and contribute to antitumor immune dysfunction, especially in the early stages.