Prognostic value of peripheral and local forkhead box P3+ regulatory T cells in patients with non-small-cell lung cancer

Several types of immunosuppressive mechanisms in cancer patients have been reported to date. Regulatory T cells (Tregs), which express the master control transcription factor forkhead box P3 (FoxP3), are considered to play a major role in hampering antitumor immune response. However, the clinical significance of Tregs in patients with lung cancer has not been fully elucidated. The aim of this study was to investigate the clinical significance of Tregs in the peripheral blood and in resected cancer tissue specimens. We analyzed peripheral blood mononuclear cells (PBMCs) collected prior to surgery and resected specimens obtained from 67 patients with non-small-cell lung cancer (NSCLC). Peripheral Tregs (pTregs) were detected as CD4+ and FoxP3+ cells by flow cytometry. Immunohistochemical staining for CD4, CD8 and FoxP3 expression was also performed quantitatively by analyzing three randomly selected fields from central regions (cCD4, cCD8 and cFoxP3) and interstitial regions of the tumors (iCD4, iCD8 and iFoxP3). The associations between the expression frequencies in selected cells and clinicopathological parameters were statistically analyzed. The frequency of pTregs was found to be significantly higher in patients with pleural invasion (P=0.0049), vessel invasion (P=0.0009), lymphatic vessel invasion (P=0.0053) and recurrent disease (P=0.0112). Patients with T1 exhibited a significantly higher frequency of cCD4 (P=0.0199) and cCD8 (P=0.0058), although cFoxP3 expression was not significant (P=0.0935). Patients with low levels of cFoxP3/iFoxP3 exhibited a significantly higher frequency of pTregs (P=0.0338) and patients with a high frequency of pTregs exhibited significantly poorer recurrence-free survival (P=0.0071). The multivariate analysis identified pTreg frequency as an independent prognostic factor (P=0.0458). Although the pathological analysis remains controversial, the frequency of pTregs in NSCLC patients may be a useful prognostic biomarker.