Suzhou Tuohua Biotechnology Co., Ltd

Primary objective: To evaluate the safety and tolerability of human umbilical cord mesenchymal stem cell injection in the treatment of moderate/severe acute respiratory distress syndrome. Secondary objective: To explore the efficacy and appropriate dose of human umbilical cord mesenchymal stem cell injection in the treatment of moderate/severe acute respiratory distress syndrome. Exploratory objective: To explore the immunogenicity and PK/PD characteristics of a single dose of human umbilical cord mesenchymal stem cell injection in patients with moderate and severe acute respiratory distress syndrome.