Anti-CD137 reverses cutaneous GVHD. Anti-CD137 (200 μg per mouse) was administered one time 34 days after induction of cGVHD and changes of clinical scores and body weight were evaluated thereafter. Data were combined from 3 experiments (n = 14 for control Ig group; n = 18 for anti-CD137 group). (Ai) Changes of mean clinical scores. *P < .05, between the 2 groups. (Aii) Changes of body weight. (B) Comparison of the percentage of mice with ulcers between day 34 and day 58 after disease induction. (C) Gross observation of the skin lesions in the posterior neck area at day 58. (D) Histopathology of the skin at day 58. (Upper column) H&E staining; (lower column) Masson trichrome staining. Images were acquired by a BX51 Olympus light microscope (Tokyo, Japan) 4×/0.10 oil objective, and an Olympus C-3000 zoom camera and processed using Image-Pro Plus, version 4 (MediaCybernetics, Silver Spring, MD). Original magnification, 40 ×.