Narrow-Band Ultraviolet B Phototherapy Ameliorates Acute Graft-Versus-Host Disease of the Intestine by Expansion of Regulatory T Cells

Narrowband ultraviolet B (NB-UVB) has been widely used in dermatological phototherapy. As for the application of NB-UVB phototherapy to graft-versus-host disease (GVHD), we previously reported that it was highly efficacious for cutaneous lesions of acute GVHD (aGVHD) and that expansion of regulatory T (Treg) cells induced by NB-UVB might be one of the mechanisms. In order to examine whether NB-UVB irradiation through expansion of Treg cells is effective for the treatment of not only cutaneous aGVHD but also aGVHD of inner organs such as the intestine or liver, we conducted experiments in which a murine lethal aGVHD model, characterized by severe involvement of the intestine, was irradiated with NB-UVB. We found that NB-UVB irradiation improved the clinical score and survival rate. The pathological score of aGVHD was improved in all affected organs: intestine, liver, and skin. In the serum of mice irradiated with NB-UVB, the levels of Treg cells-associated cytokines such as transforming growth factor beta (TGFβ) and interleukin-10 (IL-10) were elevated. The numbers of infiltrating Treg cells in inflamed tissue of the intestine and those in spleen were increased in mice treated with NB-UVB. This is the first report demonstrating that NB-UVB phototherapy has the ability to ameliorate intestinal aGVHD through the expansion of Treg cells.