COVID-19(62) Treatment(55) MSCs(46) MSC(41) stem cell(37) Patient(37) SARS-CoV-2(32) therapy(31) clinical trial(29) syndrome(29) Cell(29) ARDS(27) Efficacy(26) effective(24) Mesenchymal stem cells(23) Cell therapy(22) mesenchymal stem cell(22) therapeutic(22) caused(22) stem cells(21) Coronavirus disease 2019(21) umbilical(20) acute respiratory distress(19) Safe(19) Mesenchymal stromal cells(19) lung(19) Infection(18) IL-6(18) severe COVID-19(17) stromal cell(17)