Bone Marrow Mesenchymal Stem Cell-Derived Extracellular Vesicle Infusion for the Treatment of Respiratory Failure From COVID-19: A Randomized, Placebo-Controlled Dosing Clinical Trial

Chest. 2023 Dec;164(6):1444-1453. doi: 10.1016/j.chest.2023.06.024. Epub 2023 Jun 23.


Background: Bone marrow mesenchymal stem cell (BM-MSC)-derived extracellular vesicles (ExoFlo) convey the immunomodulatory and regenerative properties of intact BM-MSCs. This study aimed to determine the safety and efficacy of ExoFlo as treatment for moderate to severe ARDS in patients with severe COVID-19.

Research question: Do two doses of ExoFlo safely reduce mortality in COVID-19-associated moderate to severe ARDS compared with placebo?

Study design and methods: A prospective phase 2 multicenter double-anonymized randomized placebo-controlled dosing trial was conducted at five sites across the United States with infusions of placebo, 10 mL of ExoFlo, or 15 mL of ExoFlo on days 1 and 4. Patients (N = 102) with COVID-19-associated moderate to severe ARDS were enrolled and randomized to treatment. Adverse events were documented throughout the study. The primary outcome measure was all-cause 60-day mortality rate. Secondary outcomes included time to death (overall mortality); the incidence of treatment-emergent serious adverse events; proportion of discharged patients at 7, 30, and 60 days; time to hospital discharge; and ventilation-free days.

Results: No treatment-related adverse events were reported. Mortality (60-day) in the intention-to-treat population was reduced with 15 mL ExoFlo mixed with 85 mL normal saline (ExoFlo-15) compared with placebo (not significant, χ2, P = .1343). For the post hoc subgroup analyses, 60-day mortality was decreased with ExoFlo-15 compared with placebo (relative risk, 0.385; 95% CI, 0.159-0.931; P = .0340; n = 50). With ExoFlo-15, a relative risk of 0.423 (95% CI, 0.173-1.032; P = .0588; n = 24) was determined for participants aged 18 to 65 years with moderate to severe ARDS. Ventilation-free days improved with ExoFlo-15 (P = .0455; n = 50) for all participants aged 18 to 65 years.

Interpretation: The 15 mL dose of ExoFlo was found to be safe in patients with severe or critical COVID-19-associated respiratory failure. In participants aged 18 to 65 years, the risk reduction in 60-day mortality was further improved from subjects of all ages in the intention-to-treat population after two doses of 15 mL of ExoFlo compared with placebo.

Clinical trial registration:; No.: NCT04493242; URL: www.

Clinicaltrials: gov.

Keywords: COVID-19; bone marrow mesenchymal stem cell; efficacy; extracellular vesicle; safety.

Publication types

  • Randomized Controlled Trial
  • Multicenter Study
  • Clinical Trial, Phase II
  • Research Support, Non-U.S. Gov't

MeSH terms

  • COVID-19* / complications
  • COVID-19* / therapy
  • Double-Blind Method
  • Extracellular Vesicles*
  • Humans
  • Mesenchymal Stem Cells*
  • Prospective Studies
  • Respiratory Distress Syndrome* / therapy
  • Respiratory Insufficiency*
  • Treatment Outcome

Associated data