<qa>  What is a common, serious, and too often fatal, complication after matchedThis research study investigates the benefits and possible risks of adding both etanercept Enbrel and ECP extracorporeal photopheresis to the conventional preventative or prophylactic treatments for graft-versus-host disease GVHD. GVHD is a common, serious, and too often fatal, complication after matched unrelated donor stem cell transplantation, regardless of the pre-transplant conditioning regimen used full or reduced intensity. 