Study of Efficacy and Safety of Ruxolitinib in Patients With Grade II to IV Steroid-refractory Acute Graft vs. Host Disease

The purpose of this study is to assess the efficacy and safety of ruxolitinib therapy in Chinese adults and adolescents (≥ 12 years old) with Grade II-IV steroid-refractory acute graft versus host disease (SR-aGvHD).

Key Inclusion criteria * Male or female Chinese participants aged 12 or older at the time of informed consent. Written informed consent from participant, parent or legal guardian. * Able to swallow tablets. * Have undergone alloSCT from any donor source (matched unrelated donor, sibling, haplo-identical) using bone marrow, peripheral blood stem cells, or cord blood. * Clinically diagnosed Grades II to IV acute GvHD as per standard criteria occurring after alloSCT requiring systemic immune suppressive therapy. * Evident myeloid and platelet engraftment (confirmed within 48 hours prior to study treatment (ruxolitinib) start): * Confirmed diagnosis of steroid refractory aGvHD defined as participants administered systemic corticosteroids (methylprednisolone at least 1 mg/kg/day \[or equivalent prednisone dose at least 1.25 mg/kg/day\]), given alone or combined with calcineurin inhibitors (CNI) and either: 1. Progression based on organ assessment after at least 3 days compared to organ stage at the time of initiation of systemic corticosteroid +/- CNI for the treatment of Grade II to IV aGvHD. OR 2. Failure to achieve at a minimum partial response based on organ assessment after 7 days compared to organ stage at the time of initiation of systemic corticosteroid +/-CNI for the treatment of Grade II to IV. OR 3. Participants who fail corticosteroid taper defined as fulfilling either one of the following criteria: * Requirement for an increase in the corticosteroid dose to methylprednisolone ≥ 1 mg/kg/day (or equivalent prednisone dose ≥ 1.25 mg/kg/day). OR * Failure to taper the methylprednisolone dose to \< 0.5 mg/kg/day (or equivalent prednisone dose \