Mechanism of Increased Treg Frequency Induced by Irradiated Esophageal Squamous Cell Carcinoma

Abstract

<h3>Purpose/Objective(s)</h3> The infiltration of CD4+CD25+Foxp3+ regulatory T cells (Treg) in the tumor microenvironment is one of the main reasons for radiation resistance and tumor recurrence after radiotherapy. It has been established that Treg is more resistant to radiation than other T cells, but the proliferation of immune cells after radiotherapy is affected by other factors, including tumor cells. Treg frequency in the tumor microenvironment after radiotherapy has not been defined. We studied the effect and mechanism of increased Treg frequency induced by irradiated ESCC cell, TE-1. <h3>Materials/Methods</h3> After 2 Gy irradiation, TE-1 cells were co-cultured with normal peripheral blood lymphocytes for 48 hours. Flow cytometry was used to detect Treg/CD4+T cell frequency. The mRNA expression of TGF-β1 and TGF-β2 in TE-1 was detected by qPCR, and the protein content of TGF-β1 and TGF-β2 in the medium was detected by ELISA. <h3>Results</h3> Compared with non-irradiation group, the expression of TGF-β1 and TGF-β2 in TE-1 cells of irradiation group increased, and the protein content of TGF-β1 and TGF-β2 in culture medium increased, the difference was statistically significant (<i>P</i> < 0.001). Flow cytometry showed that CD4+CD25+/CD4+Tcell and CD4+CD25+Foxp3+/CD4+Tcell were increased in the radiotherapy group after co-culture, and the difference was statistically significant (<i>P</i> < 0.001). <h3>Conclusion</h3> The expression of TGF-β1 and TGF-β2 in esophageal squamous cell carcinoma cells increased after irradiation, and the frequency of Treg induced by co-culture increased, suggesting that esophageal squamous cell carcinoma cells after radiotherapy can induce the increase of Treg cells, which may be achieved mainly through the mechanism of increasing the secretion of TGF-β1 and TGF-β2.