- current standard of care treatments for covid-19 appear to be working and the subject is clinically improving - a previous msc infusion unrelated to this trial - have any of the following medical conditions: - cardio-pulmonary resuscitation within 14 days of randomization - uncontrolled or untreated symptomatic arrhythmias. exception: subjects with controlled, asymptomatic atrial fibrillation during screening may enroll - myocardial infarction within the last 6 weeks - congestive heart failure (nyha grade 3 or 4) - pulmonary hypertension (who class iii/iv) - currently receiving extracorporeal life support or membrane oxygenation (ecls/ecmo) - alanine aminotransferase (alt) ≥ 5x upper limit of normal (uln) - relevant renal impairment (egfr < 50 ml/min) - any significant medical condition, laboratory abnormality or psychiatric illness that in the investigator's opinion would interfere or prevent the subject from safely participating in the study - pregnant or breast feeding or planning for either during the study - suspected uncontrolled active bacterial, fungal, viral, or other infection (aside from infection with covid-19) - history of a splenectomy, lung transplant or lung lobectomy; - concurrent participation in another clinical trial involving therapeutic interventions (observational study participation is acceptable). - expected survival or time to withdrawal of life-sustaining treatments expected to be < 7 days. - do not intubate order; - home mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure (cpap/bipap) used solely for sleep-disordered breathing

- current standard of care treatments for covid-19 appear to be working and the subject is clinically improving - a previous msc infusion unrelated to this trial - have any of the following medical conditions: - cardio-pulmonary resuscitation within 14 days of randomization - uncontrolled or untreated symptomatic arrhythmias. exception: subjects with controlled, asymptomatic atrial fibrillation during screening may enroll - myocardial infarction within the last 6 weeks - congestive heart failure (nyha grade 3 or 4) - pulmonary hypertension (who class iii/iv) - currently receiving extracorporeal life support or membrane oxygenation (ecls/ecmo) - alanine aminotransferase (alt) ≥ 5x upper limit of normal (uln) - relevant renal impairment (egfr < 50 ml/min) - any significant medical condition, laboratory abnormality or psychiatric illness that in the investigator's opinion would interfere or prevent the subject from safely participating in the study - pregnant or breast feeding or planning for either during the study - suspected uncontrolled active bacterial, fungal, viral, or other infection (aside from infection with covid-19) - history of a splenectomy, lung transplant or lung lobectomy; - concurrent participation in another clinical trial involving therapeutic interventions (observational study participation is acceptable). - expected survival or time to withdrawal of life-sustaining treatments expected to be < 7 days. - do not intubate order; - home mechanical ventilation (noninvasive ventilation or via tracheotomy) except for continuous positive airway pressure or bi-level positive airway pressure (cpap/bipap) used solely for sleep-disordered breathing