To evaluate the safety, toxicity and immunological effects of infusion of allogeneic bone marrow-derived human mesenchymal stem (stromal) cells (MSCs) and whether this therapy has an influence on the resolution processes in ARDS patients infected with Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Inclusion Criteria:

• COVID-19-positive subject
• Horowitz index ≤ 200
• Bilateral opacities on frontal chest radiograph, and
• requirement for positive pressure ventilation via an endotracheal tube or non-invasive ventilation
• no clinical signs of left atrial hypertension detected via echocardiography, or if measured, a Pulmonary Arterial Wedge Pressure (PAOP) less than or equal to 18 mmHg.
• Subject's Age ≥ 18 years

Exclusion Criteria:

• COVID-19-negative subject
• Subject's Age < 18 years
• More than 7 days since initiation of mechanical ventilation
• Patient, surrogate or physician not committed to full intensive care support.
• Positive Pregnancy test at the time of screening.
• Patients dependent on the sponsor, investigator and their employees, as well as persons dependent on the manufacturer of the investigational drug