In a recent phase II clinical trial, the use of IL-22 (in combination with standard immunosuppressants) for the treatment of acute GvHD showed a positive response rate of 100%, 75%, and 58% in a low-, intermediate-, and high-risk biomarker constellations, respectively (28), providing a proof-of-concept for the efficacy of IL-22 therapy. This evidence concerns the gene IL22 and acute graft versus host disease.