MSCs in COVID-19 ARDS

This will be a randomized (1:1 ratio), double blind, parallel design, placebo controlled trial. Randomization will be stratified by clinical center and by moderate versus severe ARDS. The study is designed to have three interim analyses for stopping accrual early for efficacy and futility when 30%, 45% and 60% of the 300 patients have reached the primary endpoint using Bayesian predictive probabilities. Patients will be randomized in a 1:1 allocation to intravenous infusion of MSCs (remestemcel-L) plus standard of care versus placebo plus standard of care for the treatment of COVID-19 related ARDS: * Group 1: 2x10\^6 MSC/kg of body weight plus standard of care, administered twice during the first week, with the second infusion at 4 days following the first infusion (± 1 day) * Group 2: Placebo (Plasma-Lyte) plus standard of care, administered twice during the first week, with the second infusion at 4 days following the first infusion (± 1 day) (control) MSCs and placebo will initially be administered intravenously in the dose defined above at randomization. The rate of infusion may be tailored to the patient's respiratory status and fluid status, but the duration of infusion should not exceed 60 minutes. Patients will be followed for 90 days post randomization, with assessment of pulmonary symptoms at 6 and 12 months.