Table 1.

Characteristics of included studies.

References	Study design	Country	Case definition	Control definition	Morbidity definition
Meng et al. (18)	Non-randomized clinical trial	China	Received UC-MSC and standard COVID-treatment regimens	Received standard COVID-treatment regimens	Mechanical ventilation
Häberle et al. (19)	Non-randomized clinical trial	Germany	Received MSC transplantation	Received standard therapy	Acute kidney injury (any level)
Leng et al. (20)	Non-randomized clinical trial	China	Received MSCs transplant	Received placebo control	Not discharging from hospital until the end of the study
Nesrin et al. (21)	Non-randomized clinical trial	Turkey	Received MSCs transplantation	Reviewed without MSCs transplantation	Not discharging from ICU until the end of the study
Xu et al. (22)	Non-randomized clinical trial	China	Received MSC infusion and concomitant medication	Received concomitant medication	Multiple organ dysfunction syndrome (MODS)
Giacomo et al. (23)	RCT	USA	Received UC-MSC treatment	Received control treatment	Any serious adverse event
Lei et al. (24)	RCT	China	Received UC-MSC treatment	Received control treatment	Any adverse event
Shu et al. (25)	RCT	China	Received UC-MSC treatment	Received placebo treatment	No clinical improvement after 28 day
Gina Marcela Torres et al. (26)	RCT	UAE	Received COVID 19 standard care plus nebulization with NHPBSC	Received COVID 19 standard care	Continuous renal replacement therapy for AKI with hemodialysis
Dynasty (27)	RCT	Russia	Received standard therapy and MSCs derived exosomes	Received standard therapy and inhalation placebo solution	Serious and Non-serious Adverse Events During Trial

AKI, acute kidney injury; ICU, intensive care unit; MSC, mesenchymal stem cell; NHPBSC, non-hematopoietic peripheral blood stem cell; RCT, randomized controlled trial; UC-MSC, umbilical cord-derived MSC.