[Effect of concurrent chemoradiotherapy and radiotherapy alone on peripheral myeloid-derived suppressor and T regulatory cells in patients with nasopharyngeal cancer]

Objective: To investigate the percentage of myeloid-derived suppressor cells (MDSC) and T regulatory cells (Treg) in peripheral blood of nasopharyngeal cancer (NPC) patients undergoing concurrent chemoradiotherapy or radiotherapy alone. Methods: Sixty NPC patients who received radiotherapy or concurrent chemoradiotherapy from September 2012 to November 2015 and 20 healthy individuals were included in this study. For the patients, the blood samples were collected at four time points: pre-radiation (Pre-RT), reaching a dose of 40 Gy (RT-40 Gy), finishing radiation (RT-finish) and three months after finishing radiation (3m-post-RT). Flow cytometry was used to evaluate the percentage of Treg (CD4(+) CD25(+) CD127(low/-)) and MDSC (HLA-DR(-)CD11b(+) CD33(+) ) cells in peripheral blood. Results: Treg and MDSC cells were present in peripheral blood lymphocytes of healthy individuals as a percentage of (7.50±1.62)% and (1.08±0.48)%, respectively. The proportions of peripheral Treg cells in patients at Pre-RT, RT-40 Gy, RT-finish and 3m-post-RT time points were (8.42± 1.52)%, (9.10±1.57)%, (8.87±1.56)% and (7.31±1.43)%, respectively, showing a statistically significant difference between Pre-RT and the other groups (P<0.05). At Pre-RT point, the percentage of Treg cells in Stage Ⅲ-Ⅳ patients [(8.63±1.39)%] was higher than that in Stage Ⅰ-Ⅱ [(7.65±1.94)%, P=0.042]. Moreover, the proportions of peripheral MDSC cells in patients at Pre-RT, RT-40 Gy, RT-finish and 3m-post-RT time points were (2.14±1.21)%, (4.08±1.90)%, (3.76±1.31)% and (1.52±0.88)%, respectively. The percentages of MDSC cells at RT-40 Gy and RT-finish points were significantly higher than those at Pre-RT, while the percentage of MDSC cells at 3m-post-RT was significantly lower than those at Pre-RT (P<0.05). At Pre-RT point, the percentage of MDSC cells in Stage Ⅲ-Ⅳ patients [(2.25±1.26)%] was higher than that in Stage Ⅰ-Ⅱ [(1.35±0.66)%, P=0.007]. At RT-finish point, the proportions of MDSC and Treg cells in patients with Ⅲ-Ⅳ grade of radiation induced oral mucositis [(4.41±1.27)% and (9.91±1.23)%] were significantly higher than those in Ⅰ-Ⅱ grade patients [(3.15±1.04)% and (8.41±1.52)%, both of P<0.05]. Conclusions: The proportions of MDSC and Treg cells in initial treated NPC patients are higher than healthy individuals, and they are also associated with the tumor stages. During the concurrent chemoradiotherapy and radiation, the percentage of MDSC and Treg cells is elevated, suggesting a decreased immune activity. The increase of MDSC and Treg cells is related to radiation induced oral mucositis.