Use of hUC-MSC Product (BX-U001) for the Treatment of COVID-19 With ARDS

Inclusion Criteria: 1. Male or female, aged between 18 and 80; 2. Laboratory (RT-PCR, Gene Sequencing or Antibody) confirmed cases of severe COVID-19 pneumonia with mild to moderate ARDS (Berlin definition); 3. Patients are intubated; 4. Patients who voluntarily adhere to the research procedures and ensure good compliance during the research period; 5. Patients who fully understand the research nature of this study and sign written informed consent. Exclusion Criteria: 1. Subjects who have received investigational drug (except for Remdesivir) for the treatment of COVID-19 within 30 days before screening; 2. Subjects who are pregnant, breastfeeding or whose urinary pregnancy test is positive before participation in the study; subjects who are pregnant, breastfeeding, have a birth plan, or are unwillingness to use contraception during the study period and within 12 months of infusion; except for subjects who have sterilization surgery or menopause during the study period; 3. Within 3 days before screening/randomization, subjects who have used high-dose corticosteroids that is equivalent to methylprednisolone \>240 mg/day or irregular use of systemic corticosteroids to treat other diseases that could affect the efficacy evaluated by the investigator; 4. Subjects receiving extracorporeal membrane oxygenation (ECMO) support. 5. Subjects who are allergic to low-molecular-weight heparin calcium or human albumin; 6. Subjects with ongoing malignant tumors.