Steroids Versus ECP and Steroids as First-line Treatment of Grade II Acute GVHD

Inclusion Criteria: * Age \> 18 years, * allogeneic hematopoietic stem cell transplantation received (from any type of graft and donor) after malignant or non malignant disease * patient suffering from Grade II acute GVHD with skin +/- high GI involvement (stage 2-3 skin + upper gastrointestinal tract or skin stage 3) in the 3 months following stem cell transplantation * patient requiring first line treatment for acute GVHD * patient able to start PCE therapy in the 3 days after randomization * validation of the presence of a peripheral or central venous access (its type should be conform to the recommendations described in the Therakos Cellex operator manual), allowing to perform PCE sessions weekly during 3 months. In the absence of appropriate preexisting central line at inclusion, peripheral access will be preferred. * leukocytes \> 1.5 G/l, platelets \> 30 G/l, hematocrit \> 27% (blood transfusion are permitted), based on the last available blood testing results, * patient with French Health Insurance, * patient informed about the clinical trial content and organization, * informed consent form signed. Exclusion Criteria: * \- Grade 1 acute GVHD, * acute GVH grade \> II or acute GVH with lower gastrointestinal tract or with liver involvement, * relapse of the hematologic disease at time of acute GVHD, * uncontrolled ongoing infection at time of inclusion: bacterial or fungal infections, CMV reactivation with increasing CMV viral load, * HIV positivity or replicative HBV or HCV infection (based on pre-transplant assessment), * patient with allergy or contraindications to UVADEX, extracorporeal photopheresis, steroids, or posaconazole (see details in the study protocol), * woman of childbearing age without efficient contraceptive method, pregnancy or breast feeding woman, * patient with history of profound venous thrombosis in the last 5 years, * patient included in another acute GVHD prospective clinical trial.