Treatment of Chronic Graft Versus Host Disease With Arsenic Trioxide

Inclusion Criteria: * Adult patients (≥18 years) who have received a first allogeneic stem cell transplantation for a hematological disease (any source of hematopoietic stem cells is authorized; any category of conditioning regimen prior to allo-SCT is authorized; any type of stem cell donors is authorized) * Confirmed diagnosis of a first episode of chronic GvHD requiring systemic immunosuppressive therapy (any prior GvHD prophylaxis previously used is accepted). Chronic GvHD diagnosis is defined according to the NIH Working Group Consensus. Chronic GvHD diagnosis will be based on the evaluation of the severity of the different clinical manifestations including: * Performance status evaluation * Cutaneous evaluation measured by the percentage of extension or the presence of sclerotic features. If relevant, confirmation with a biopsy should be performed whenever possible * Oral symptoms * Ocular symptoms * Gastro-intestinal symptoms * Evaluation of liver involvement (total bilirubin, transaminases and alkaline phosphatases) * Pulmonary function evaluation * Evaluation of the musculoskeletal manifestations, especially the amplitude of the relevant articulations * Genital tract symptoms * Signed informed consent * Absence of contra-indications to the use of ATO * Subjects affiliated with an appropriate social security system * Men must use a medically acceptable method of contraception throughout the treatment period and for at least 4 months and 10 days following the last treatment administration * Women who are of childbearing potential must have a negative serum pregnancy test and agree to use a medically acceptable method of contraception throughout the study and for 3 months following the end of the study * Patient not participating or not having participated in a clinical study in the 30 days prior to his/her inclusion in the study Exclusion Criteria: * Patient developing acute GvHD (whether early or "late onset" form) * Patients developing overlap GvHD as defined by the 2014 NIH Working Group Consensus (presence of one or more acute GvHD manifestations in a patient with a diagnosis of chronic GvHD) * A "mild" form of chronic GvHD not requiring systemic immunosuppressive therapy * A "moderate" form of chronic GvHD limited to one organ site not requiring systemic immunosuppressive therapy * Patient receiving mycophenolate mofetil * Not the first episode of chronic GvHD needing systemic immunosuppressive therapy * Second allogeneic stem cell transplant * Severe cardiac diseases (congestive heart failure (NYHA class III), recent myocardial infarction (in the past 6 months before the inclusion), histories of unexplained syncope, ...) * Significant arrhythmias, electrocardiogram (EKG) abnormalities: * Congenital QT syndromes * History or presence of significant ventricular or atrial tachyarrhythmia * Clinically significant resting bradycardia (\< 50 beats per minutes) * QTc\>450msecformenand\>470msecfor women on screening EKG (using the QTcF formula) * Right bundle branch block plus left anterior hemiblock, bifascicular block * Central or peripheral neuropathy * Neutrophils \< 0.5 × 109/L * Platelets \< 50 × 109/L * Potassium ≤ 4 mEq/l\* * Magnesium ≤ 1.8 mg/dl\* * Calcium ≤ 2.15 mmol/l\* * Hepatic impairment due to a suspected or proven liver damage, other than direct hepatic cGvHD involvement * PT \< 50% * Renal impairment (creatinine ≥ 100 μmol/l) * Uncontrolled systemic infection which in the opinion of the investigator is associated with an increased risk of the patients' death within 1 month after the start of therapy * Severe neurological or psychiatric disorders * Denied informed consent * Pregnancy * Women breastfeeding at selection and throughout the treatment period * If abnormal at selection, to be corrected and re-validated following electrolytes infusion, before inclusion and each drug perfusion.