Here is the design of a clinical trial:

Official Title: Double-blind, Randomized, Controlled, Clinical Trial to Assess the Efficacy of Allogenic Mesenchymal Stromal Cells in Patients With Acute Respiratory Distress Syndrome Due to COVID-19

Included conditions:
- Acute Respiratory Distress Syndrome
- COVID-19 Pneumonia

Study Armgroups:
- {'label': 'Mesenchymal Stromal cells', 'type': 'EXPERIMENTAL', 'description': 'Approximately 1x10E6 MSC/kg', 'interventionNames': ['Biological: Mesenchymal stromal cells']}
- {'label': 'Control group', 'type': 'PLACEBO_COMPARATOR', 'description': 'Solution identical to experimental treatment, without the MSC', 'interventionNames': ['Other: Placebo']}

Interventions:
- {'type': 'BIOLOGICAL', 'name': 'Mesenchymal stromal cells', 'description': 'Administration of one single dose of allogenic Mesenchymal stromal cells', 'armGroupLabels': ['Mesenchymal Stromal cells']}
- {'type': 'OTHER', 'name': 'Placebo', 'description': 'Administration of placebo (solution identical to experimental treatment, without the MSC)', 'armGroupLabels': ['Control group']}

Primary Outcomes:
- {'measure': 'Change in the PaO2/FiO2* ratio from baseline to day 7 of treatment administration', 'description': 'Primary endpoint', 'timeFrame': '7 days'}

Please estimate the sample size based on the assumption: 
Not specified
Numbers to be randomised (sample size)
          A total of 20 participants are planned to be randomized, 10 to each treatment group.