Human mesenchymal stem cell therapy in severe COVID-19 patients: 2-year follow-up results of a randomized, double-blind, placebo-controlled trialResearch in context oleh Tian-Tian Li, Bo Zhang, Hui Fang, Ming Shi, Wei-Qi Yao, Yuanyuan Li, Chao Zhang, Jinwen Song, Lei Huang, Zhe Xu, Xin Yuan, Jun-Liang Fu, Cheng Zhen, Yu Zhang, Ze-Rui Wang, Zi-Ying Zhang, Meng-Qi Yuan, Tengyun Dong, Ruidan Bai, Lulu Zhao, Jianming Cai, Jinghui Dong, Jianzeng Zhang, Wei-Fen Xie, Yonggang Li, Lei Shi, Fu-Sheng Wang