A Study Comparing Corticosteroids Alone Versus Corticosteroids and Extracorporal Photopheresis (ECP) as First-line Treatment of Standard II Acute Graft-versus-host Disease

Inclusion Criteria: * Age ≥ 18 years ; * Having received an allogeneic stem cell transplantation for any malignant or non-malignant hemopathy and whatever the type of donor and graft. * with grade II acute GVHD with skin involvement (stage 1-3 skin +/- stage 1 gastro intestinal) in the 3 months following the allogeneic stem cell transplantation * acute GVHD in the first line treatment * validation of the presence of peripheral or central venous access allowing to perform 2 ECP per week during 3 months. In the absence of a pre-existing and adpated central catheter at the time of inclusion, peripheral venous access will be preferred * Leucocytes \> 1.5 G/L * Platelets \> 30 G/L, Haematocrite \> 27% (allowed transfusions) * Patient affiliated to a French Social Security regimen * information consent form signed. Exclusion Criteria: * acute GVHD of grade I * acute GVHD of grade \> II * progressive hematologic disease at inclusion * uncontrolled ongoing infection at time of inclusion: bacterial or fungal infections, increasing CMV viral load. * patient with HIV positivity or replicative HBV or HCV infection * Contraindications for UVADEX / photopheresis / stéroids / posaconazole / heparin * Patient with a history of deep venous thrombosis * Pregnancy * Women of child bearing potentiel not using contaception