Safety and Tolerance of Umbilical Cord Mesenchymal Stem Cells in Patients With Acute Respiratory Distress Syndrome

Inclusion Criteria: * 18-75 years old (including the threshold), male or female * A definite diagnosis of mild to moderate acute respiratory distress syndrome (ARDS) (according to the ARDS Berlin definition and diagnostic criteria) * ARDS onset ≤ 5 days * 100 mmHg \< PaO2/FiO2 ≤ 300 mmHg * Bilateral pulmonary infiltrates on chest radiograph or chest CT * Rule out other causes of pulmonary oedema, such as cardiogenic pulmonary oedema and pulmonary oedema due to fluid overload * Have no plans to have children within 2 weeks before screening and 3 months after the end of the trial, and agree to use effective non-pharmacological contraception during the trial * Patients voluntarily signed an informed consent form and were willing to co-operate with the trial process Exclusion Criteria: * Hypersensitivity to known components of the drug (the main component of this product is human umbilical cord mesenchymal stem cells, excipients include dimethyl sulfoxide, human albumin, compound electrolyte injection), the presence of a history of allergy to gentamicin or other history of severe allergy * Patients requiring treatment for any malignancy within 2 years prior to administration (except non-melanoma skin cancer) * Lung transplant patients * Patients with malignant haematological diseases * Persons who have had a cardiovascular event within 3 months prior to dosing (e.g., unstable angina, congestive heart failure, myocardial infarction within the last 12 months, haemodynamic instab…