<qa>  What is the name of the clinical trial that studies biomarkers in predicting response in patientsThis clinical trial studies biomarkers in predicting response in patients with graft-versus-host disease GVHD undergoing extracorporeal photopheresis ECP. ECP treats the patients blood with ultraviolet light outside the body and kills the white blood cells before returning blood back into the patients body. Studying samples of blood from patients with GVHD may help doctors identify and learn more about biomarkers related to GVHD. 