Human CCR6+ Th17 Lymphocytes Are Highly Sensitive to Radiation-Induced Senescence and Are a Potential Target for Prevention of Radiation-Induced Toxicity.

Purpose: This study addresses the sensitivity of different peripheral CD4(+) T-lymphocyte subsets to irradiation (IR) and identifies potential targets for the prevention or treatment of radiation-induced toxicity. Methods: This study was performed on peripheral blood mononuclear cells or sorted peripheral memory lymphocytes of CCR6(+) mucosa-homing Th17/CCR6(neg)Th and regulatory T subtypes of healthy volunteers. Cells were irradiated with a 2 Gy with or without pharmacologic inhibitors of different signaling pathways. Senescence of irradiated cells was assessed by resistance to apoptosis and determination of various senescence-associated biomarkers (senescence associated b-galactosidase activity, p16Ink4a-, p21Cdkn1a-, gH2A.X-, H2A.J expression). Cytokine production was measured in supernatants of irradiated cells by Luminex technology. Results: Not all CD4(+) memory T lymphocyte subsets were equally radiosensitive. High sensitivity of CCR6(+)Th17 lymphocytes to IR-induced senescence was shown by expression of the histone variant H2A.J, higher SA-b-Gal activity, and upregulation of p16(Ink4a) and p21(cdkn1a) expression. Lower Annexin V staining and cleaved caspase3, and higher expression of antiapoptotic genes Bcl-2 and Bcl-xL LF, showed that CCR6(+)Th17 lymphocytes were more resistant to IR-induced apoptosis than CCR6(neg) memory Th and regulatory T lymphocytes. After a 2 Gy IR, both CCR6(+)Th17 and CCR6(neg) cells acquired a moderate senescence-associated secretory phenotype, but only CCR6(+)Th17 cells secreted interleukin 8 (IL-8) and vascular endothelial growth factor-A (VEGF-A). Pharmacologic targeting of reactive oxygen species (ROS), mitogen-activated protein kinases (MAPKs), and mammalian target of rapamycin (mTOR) signaling pathways prevented the expression of senescent markers and IL-8 and VEGF-A expression by CCR6(+)Th17 cells after IR. Conclusions: This study suggests that IR induces senescence of CCR6(+)Th17 lymphocytes associated with secretion of IL-8 and VEGF-A that may be detrimental to the irradiated tissue. ROS-MAPKs signaling pathways are candidate targets to prevent this CCR6(+)Th17-dependent radiation-induced potential toxicity. Finally, the ratio of circulating H2A.J(+) senescent CCR6(+)Th17/CD4(+) T lymphocytes may be a candidate marker of individual intrinsic radiosensitivity. (C) 2019 Elsevier Inc. All rights reserved.