Abstract
BACKGROUND: Prior clinical trials established the safety, but not the efficacy of bone marrow-derived mesenchymal stromal cells (MSCs) in the acute respiratory distress syndrome (ARDS). METHODS: We conducted a prospective, double-blind, multi-center randomized phase 2b clinical trial of one dose of intravenous MSCs (10 x 10(6)/kg predicted body weight) versus placebo in 120 ventilated patients with ARDS (PaO(2)/FiO(2) < 250 mmHg). The primary endpoint was change in oxygenation index (OI) over 36 hours from baseline. FINDINGS: Enrollment began in January 2020. Due to the Coronavirus 2019 (COVID-19) pandemic, the majority of subjects (101/120, 84%) developed ARDS from COVID-19. There were no significant baseline differences in severity of illness between patients treated with MSCs and those who received placebo in the entire cohort of 120 patients or in the 101 patients with COVID-19 ARDS. There was no difference in the primary endpoint of change in oxygenation index from baseline over 36 hours after study product administration for the entire cohort or the COVID-19 subgroup, nor were there significant differences in mortality at 14, 28, 60 or 180 days. Plasma protein biomarker and gene expression analyses identified sub-groups of patients with differential treatment responses in terms of clinical outcomes. INTERPRETATION: This phase 2b clinical trial identified no physiologic or clinical benefit from a single dose of MSCs in patients with ARDS, including those with COVID-19 ARDS. In future trials, baseline plasma biological markers may help identify patients who are more likely to benefit from MSCs therapy. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/). Clinical trial registration available at www. CLINICALTRIALS: gov, ID: NCT03818854.