Evaluation of EFficacy and SaFEty of Leukotac (Inolimomab) in Pediatric Patients With SR-aGvHD

Inclusion Criteria: * Patients who develop a first episode of aGvHD stage ≥ II (Przepiorka et al., 1995), resistant to a first line therapy with steroids (lack of improvement after 5 days or progression after 3 days of treatment with corticosteroids at 2 mg/Kg methylprednisolone equivalent dose) * Age 28 days to \< 18 years old * Allo-HSCT with any type of donor, stem cell source, GVHD prophylaxis or conditioning regimen * Patients receiving Allo-HSCT for any indication (i.e. malignant or non-malignant disease) * Signature of informed and written consent by the patient and/or by the patient's legally acceptable representative(s) Exclusion Criteria: * Isolated stage 1 skin SR-aGvHD * Overlap chronic GvHD as defined by the NIH Consensus Criteria (Jagasia MH, 2015) * Acute GvHD after donor lymphocytes infusion (DLI) * Relapsed/persistent malignancy requiring rapid immune suppression withdrawal * Other systemic drugs than corticosteroids for GvHD treatment (including extra-corporeal photopheresis). Drugs already being used for GvHD prevention (e.g. calcineurin inhibitors) are allowed. * Active, uncontrolled bacterial, viral, or fungal infection requiring systemic therapy * Known allergy or intolerance to Leukotac of one of its ingredients * Pregnancy: positive urinary or blood test in female of childbearing potential; lactation; absence of effective contraceptive method for female and male of childbearing potential * Other ongoing interventional protocol that might interfere with