Study design
This study was a multicentric, double-blinded, randomized, placebo-controlled trial to evaluate NA-UC-MSCs as a complementary treatment in severe COVID-19 patients (clinicaltrials.gov registration number NCT05132972 24/11/2021). This study approved by Health Research Ethics Committee, National Institute of Health Research and Development (HREC-NIHRD); ethical clearance number LB.02.01/2/KE.573/2020 extended no. LB.02.01/2/KE.582/2021. All experiments were conducted in accordance with the relevant guidelines and regulations.