Foxp3+ Regulatory T Cells and Natural Killer Cells Distinctly Infiltrate Primary Tumors and Draining Lymph Nodes in Pulmonary Adenocarcinoma

Introduction:Regulatory T cells (Tregs) can play a key role in suppressing T-cell-mediated immunity in patients with cancer. In this study, the immune cell composition of the lung tissue and draining lymph nodes from patients with non-small cell lung cancer was analyzed.Methods:Samples (solid tumor, tumor border, and tumor-free lung tissue, as well as intrapulmonal N1 and mediastinal N2 lymph nodes) from 30 patients subjected to curative resection were analyzed by immunohistochemistry and flow cytometry.Results:Immunohistochemistry showed the presence of Foxp3+ Tregs in tumor-infiltrated lung tissue, scattered Tregs in tumor-free lung samples, and a large number of these cells in metastatic lymph nodes. Using flow cytometry, we observed a significant enhancement of CD4+ T cells and Foxp3+ Tregs in the tumor center of adenocarcinoma samples, when compared with tumor-free lung tissues and tumor periphery. This enrichment was associated with a drastic decrease in natural killer cell amounts. Metastatic lymph nodes also showed higher Treg numbers than tumor-free ones in patients with lung adenocarcinomas. In contrast, patients with squamous cell carcinomas displayed less profound accumulation of Tregs.Conclusion:Accumulation of Tregs in the center of lung tumors and in metastatic lymph nodes in combination with a decrease in the natural killer cell numbers suggests a critical role of Treg in the formation of immunosuppressive tumor microenvironment. Therefore, lung cancer immunotherapy may be improved by a specific Treg elimination or suppression.