Activity, Safety and Pharmacokinetics in Pediatric Subjects With Moderate and Severe Chronic Graft vs. Host Disease After Allogeneic Stem Cell Transplant

Inclusion Criteria: * Male or female subjects age ≥28 days and \<18 years at the time of informed consent. * Subjects who have undergone a successful alloSCT from any donor source (matched unrelated donor, sibling, haplo-identical) using bone marrow, peripheral blood stem cells, or cord blood. Recipients of myeloablative or reduced intensity conditioning are eligible. * Subjects with diagnosed moderate to severe cGvHD according to NIH 2014 Consensus Criteria prior to Cycle 1 Day 1. Other possible diagnoses for clinical symptoms supporting cGvHD diagnoses must be excluded (e.g., infection, drug side effects, malignancy). Subjects must be either: * Treatment-naive cGvHD subjects that have not received any prior systemic treatment for cGvHD except for a maximum 72h of prior systemic corticosteroid therapy of methylprednisolone or equivalent after the onset of chronic GvHD. Subjects are allowed to have received prior systemic treatment for cGvHD prophylaxis (as long as the prophylaxis was started prior to the diagnosis of cGvHD). OR o Steroid-refractory moderate to severe cGvHD as per institutional criteria, or per physician decision in case institutional criteria are not available, and still receiving systemic corticosteroids for the treatment of cGvHD for a duration of \<18 months prior to Cycle 1 Day 1. In case the corticosteroids were previously interrupted due to response, the duration of \< 18 months applies to the last period of corticosteroid use. Exclusion Criteria…