Human Umbilical Cord Mesenchymal Stem Cell Transplantation for The Treatment of Acute-on-Chronic Liver Failure

Inclusion Criteria: 1. 18 years old ≤ age ≤ 70 years old, gender is not limited. 2. Meet the APASL definition of ACLF: acute liver injury in patients with previously diagnosed or undiagnosed chronic liver disease or cirrhosis, manifested as jaundice (total bilirubin levels of 5 mg/dl or more) and coagulopathy (INR of 1.5 or more, or prothrombin activity of less than 40%） complicated within 4 weeks by clinical ascites, encephalopathy, or both. 3. Willing to sign the informed consent form. Exclusion Criteria: 1. Patients with acute kidney injury, upper gastrointestinal hemorrhage, hepatic encephalopathy above grade II (inclusive) or uncontrolled infection at baseline; 2. Before the onset of liver failure, the previous indicators of the patient included PLT\<50×10\^9/L or Child-Pugh score\>9; 3. Combined with liver cancer or other malignant tumors; 4. Patients with previous liver transplantation or planned liver transplantation within 3 months; 5. Severe organic disease of primary extrahepatic organs; 6. Those who have a history of venous thrombosis or pulmonary embolism are judged by the investigator to be ineligible to participate in this trial; 7. Pregnant, breastfeeding women or those who plan to have a baby in the near future; 8. Those who are highly allergic or have a history of severe allergies; 9. Those who have received immunosuppressant and immune enhancer treatment within 1 month; 10. Drug abuse in the past 5 years; 11. Alcohol withdrawal symptoms; 12. A history of severe mental disorders within 24 months before screening, including uncontrolled major depression or controlled or uncontrolled psychosis; 13. Those who have participated or are participating in other clinical trials within three months before screening, or have previously received stem cell therapy; 14. Other conditions that the investigator thinks that the patient is not suitable to participate in this study.