Application and Research of Mesenchymal Stem Cells in Alleviating Severe Development of COVID-19 Infection

Inclusion Criteria: * Age 18-85 years;The diagnosis of COVID-19 infection was clinically classified as Moderate cases, and the criteria were based on Diagnosis and Treatment Protocol for Novel Coronavirus Pneumonia(Trial Version 10) * Having the relevant clinical manifestations of COVID-19 infection. * Having one or more of the following etiological and serological examination results * Tested positive for Novel Coronavirus nucleic acid * Tested positive for Novel Coronavirus antigen * Novel Coronavirus was isolated and cultured positive * Novel Coronavirus specific immunoglobulin G reaches a titration of at least 4-fold increase during convalescence compared with the acute phase. * Moderate cases diagnostic criteria：Persistent high fever \> 3 days or (and) cough, Tachypnea etc，but respiratory rate≧30 breaths/ min ,oxygen saturation \> 93% on finger pulse oximeter taken at rest. Radiology shows the characteristic manifestations of COVID-19 pneumonia * There are one or more of the following risk factors for the development of severe / critical severity: * Patients over 65 years old, especially those who have not been vaccinated against novel coronavirus * Patients with cardiovascular and cerebrovascular diseases (including hypertension), chronic lung disease, diabetes, chronic liver and kidney disease, tumors and other underlying diseases, as well as maintenance dialysis * Patients with immune deficiency (such as AIDS, long-term use of corticosteroids or other immunosuppressive drugs resulting in immune dysfunction) * Patients with Obesity (body mass index ≥30) * late trimester of pregnancy and perinatal women * Heavy smoker. Exclusion Criteria: * Patients with prior or present tumor history,or precancerous lesions confirmed by pathological examination. * Patients with active acute myocardial infarction or acute cerebral infarction. * Pregnant or lactating patients. * Patients with poorly controlled mental illness. * Patients addicted to alcohol or drugs. * Patients Unable or unwilling to sign informed consent or poor compliance. * Patients with active tuberculosis or influenza virus, adenovirus and other acute respiratory virus infection. * Patients deemed unsuitable for stem cell therapy by clinicians. * Patients enrolled in other clinical trials within 3 months.