Radiation Enhances Regulatory T Cell Representation

• Published in: International journal of radiation oncology, biology, physics Vol. 81; no. 4; pp. 1128 - 1135
• Main Authors: Kachikwu, Evelyn L., M.D, Iwamoto, Keisuke S., Ph.D, Liao, Yu-Pei, Ph.D, DeMarco, John J., Ph.D, Agazaryan, Nzhde, Ph.D, Economou, James S., M.D., Ph.D, McBride, William H., D.Sc, Schaue, Dörthe, Ph.D
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15.11.2011; Elsevier
• Subjects: Adenocarcinoma - immunology; Adenocarcinoma - radiotherapy; Animals; Anti-CD25 therapy; Biological and medical sciences; Biomarkers - analysis; CARCINOMAS; CD24 Antigen - analysis; CD4-Positive T-Lymphocytes - radiation effects; Cell Line, Tumor; Combined treatment; Dose-Response Relationship, Radiation; Female; Forkhead Transcription Factors - analysis; Gynecology. Andrology. Obstetrics; Hematology, Oncology and Palliative Medicine; Hindlimb - radiation effects; IMMUNOTHERAPY; Interleukin-2 Receptor alpha Subunit - analysis; IRRADIATION; LEGS; Lymph Nodes - cytology; Lymphocyte Count; LYMPHOCYTES; Male; Male genital diseases; Medical sciences; Mice; Mice, Inbred C57BL; Mice, Transgenic; Nephrology. Urinary tract diseases; PATIENTS; PROSTATE; Prostatic Neoplasms - immunology; Prostatic Neoplasms - radiotherapy; Radiation therapy; Radiation Tolerance - immunology; Radiology; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Scattering, Radiation; Spleen - cytology; T regulatory cells; T-Lymphocytes, Regulatory - immunology; T-Lymphocytes, Regulatory - radiation effects; Transgenic adenocarcinoma of mouse prostate; Treatment. General aspects; Tumors; Tumors of the urinary system; Urinary tract. Prostate gland; Whole-Body Irradiation; Anti-CD25 therapy; Radiation therapy; T regulatory cells; Transgenic adenocarcinoma of mouse prostate; Urinary system disease; Prostate disease; Rodentia; Transgenic animal; Malignant tumor; Radiotherapy; Vertebrata; Mammalia; Cancerology; Treatment; Mouse; Immunotherapy; T-Lymphocyte; Male genital diseases; Regulatory cell; Tumor cell; Cancer
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2010.09.034

Purpose Immunotherapy could be a useful adjunct to standard cytotoxic therapies such as radiation in patients with micrometastatic disease, although successful integration of immunotherapy into treatment protocols will require further understanding of how standard therapies affect the generation of antitumor immune responses. This study was undertaken to evaluate the impact of radiation therapy (RT) on immunosuppressive T regulatory (Treg) cells. Methods and Materials Treg cells were identified as a CD4+ CD25hi Foxp3+ lymphocyte subset, and their fate was followed in a murine TRAMP C1 model of prostate cancer in mice with and without RT. Results CD4+ CD25hi Foxp3+ Treg cells increased in immune organs after local leg or whole-body radiation. A large part, but not all, of this increase after leg-only irradiation could be ascribed to radiation scatter and Treg cells being intrinsically more radiation resistant than other lymphocyte subpopulations, resulting in their selection. Their functional activity on a per-cell basis was not affected by radiation exposure. Similar findings were made with mice receiving local RT to murine prostate tumors growing in the leg. The importance of the Treg cell population in the response to RT was shown by systemic elimination of Treg cells, which greatly enhanced radiation-induced tumor regression. Conclusions We conclude that Treg cells are more resistant to radiation than other lymphocytes, resulting in their preferential increase. Treg cells may form an important homeostatic mechanism for tissues injured by radiation, and in a tumor context, they may assist in immune evasion during therapy. Targeting this population may allow enhancement of radiotherapeutic benefit through immune modulation.