The present invention provides a method of diagnosing and treating Graft versus host disease (GVHD), said method comprising:a. obtaining a body fluid or tissue sample from said mammal, throughout the year post-transplant；b. detecting the expression level, phosphorylation level, or a combination thereof, of biomarkers in said body fluid or tissue sample；c. diagnosing said mammal with Graft versus host disease (GVHD) when the expression level, phosphorylation level, or a combination thereof of said biomarkers in said body fluid or tissue sample are detected with a deviation of at least about 25% from standard measurements taken from healthy subjects and/or from measurements taken from said mammal prior to said transplant； and,d. administering an effective amount of at least one immunosuppressant or steroid or a combination thereof to the diagnosed mammal.
