PDCD1 and graft versus host disease: Most animals treated with the single agents did not develop symptoms of GvHD (Grade 0) or had mild signs of rough coats and hunching (Grade 0-1) between day 24-46, and the majority survived until the end of the study (12 out of 15 in the anti-PD-1 mAb group and 14 out of 15 in the anti-CTLA-4 mAb group).