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A proposed mechanism of severe Corona virus Disease-2019 (COVID-19) is a deregulated innate immune response to an infection with SARS-CoV-2 resulting in cytokine release syndrome (CRS). Mesencymal stem cells (MSC) have been shown to have immunomodulatory effects and may attenuate the CRS. We present 11 cases of severe COVID-19 pneumonia treated with umbilical cord-derived, non-HLA matched MSC administered as four separate intravenous doses, 5×105 cells/kg. Clinical symptoms, measurements of inflammatory mediators and cytokines (IL6, IL10, IFN-γ, TNF-α), and radiological results were recorded for each patient. Although there were large variations in baseline cytokine pattern elevation, all cytokine levels decreased in all patients after the 4 infusions of UC-MSC, albeit in different magnitudes. Seven patients eventually improved in terms of need for supplemental oxygen and/or mechanical ventilation, clinical symptoms, resolution of pneumonia on imaging, and were discharged. Three patients expired, 1 of whom expired before completing the full course of therapy. This limited series of patients showed that UC-MSC therapy down regulates the cytokine storm and may improve clinical status in patients hospitalized with severe COVID-19 pneumonia without any infusion related reaction.