Treatment of Steroid-Refractory Acute Graft-versus-host Disease with Mesenchymal Stromal Cells Versus Best Available Therapy

Inclusion Criteria:

• Participant had a previous allogeneic HSCT as indicated for non-malignant (includinginborn errors of metabolism, primary immunodeficiencies, haemoglobinopathies, andbone marrow failure syndromes) or haematological malignant disease, irrespective ofhuman leukocyte antigen match

• Participant has been clinically diagnosed with Grade II to IV aGvHD at the ScreeningVisit

• Participant has experienced failure of previous first-line aGvHD treatment (ie,SR-aGvHD), defined as: a) aGvHD progression within 3 to 5 days of therapy onset with >= 2 mg/kg/day of prednisone equivalent or b) failure to improve within 5 to 7 daysof treatment initiation with >= 2 mg/kg/day of prednisone equivalent or c)incomplete response after > 28 days of immunosuppressive treatment including atleast 5 days with >= 2 mg/kg/day of prednisone equivalent

• Participant has an estimated life expectancy > 28 days at the Screening Visit

• Male or female participant who is >= 12 years of age at the Screening Visit

Exclusion Criteria:

• Participant has overt relapse or progression or persistence of the underlyingdisease at the Screening Visit

• Participant has received the last HSCT for a solid tumour disease

• Participant has GvHD overlap syndrome at the Screening Visit

• Participant has received systemic first line treatment for aGvHD other than steroidsand a prophylaxis with other than calcineurin inhibitors, mammalian target ofrapamycin (mTOR) inhibitors, anti-thymocyte globulin (ATG), mycophenolate mofetil (MMF), methotrexate (MTX), and / or cyclophosphamide before the Screening Visit

• Participant has a known pregnancy (as confirmed by a positive pregnancy test at theScreening Visit) and or is breastfeeding at the Screening Visit

• Participant has received treatment with any other investigational agent within 30days or 5 half-lives (whichever is longer) before the Screening Visit (compliance tobe confirmed for the period between the Screening Visit and the Baseline Visit atthe Baseline Visit).