BAttLe Against COVID-19 Using MesenchYmal Stromal Cells

Inclusion Criteria: * Patients of both sexes. * Over 18 years. * Confirmation of SARS-COV-2 infection by RT-PCR in respiratory sample. * Respiratory failure requiring intubation and connection to mechanical ventilation, secondary to SARS-CoV-2 infection. * Criteria for acute respiratory distress: acute bilateral alveolar-interstitial infiltrate not compatible with left ventricular failure (demonstrated with ultrasound or hemodynamic parameters), sudden onset, and blood gas compromise with a PaO2 / FiO2 ratio \<200 mm-Hg. * Women of childbearing potential should have a negative urine pregnancy test performed at the time of study enrollment. * Written or verbal informed consent from the patient, family member or legal representative. Exclusion Criteria: * Any other cause of acute respiratory distress not attributable to SARS-Cov-2. * RT-PCR of SARS-Cov-2 negative. * Multi-organ failure (more than three organs) * Severe respiratory failure requiring extracorporeal support (ECMO) Grave Moderate severe COPD requiring chronic home oxygen therapy, need for prior home oxygen therapy for any reason. * Pregnancy, lactation and women of childbearing age but who do not take effective contraceptive measures. * Active tumor disease. * Previous immunosuppressive treatment. * Allergy or hypersensitivity to the administered products. * History of deep vein thrombosis or pulmonary embolism in the last 3 years. * Participation in other clinical trials during the 3 months prior to the initial visit.