Novel Coronavirus Induced Severe Pneumonia Treated by Dental Pulp Mesenchymal Stem Cells

Inclusion Criteria: * 1\. Age ≥ 18, age ≤ 75, gender unlimited; * 2\. novel coronavirus diagnosed severe pneumonia and confirmed no effective treatment plan. (severe patients meet any of the following: (1) respiratory distress, RR \> 30 times / minute; (2) resting state, oxygen saturation is less than 93%; (3) arterial oxygen partial pressure (PaO2) / oxygen inhalation (FiO2) is less than 300 mmHg (1mm Hg=0.133 kPa). * 3\. Those who voluntarily participate in the clinical study and can cooperate with researchers to carry out the study, and the patients themselves or their legal representatives voluntarily sign the informed consent. Exclusion Criteria: * 1\. Patients with autoimmune diseases in the past or screening; * 2\. Those who have serious basic diseases that affect their survival, including: malignant tumor, hematopathy, malignant fluid, active hemorrhage, severe malnutrition, etc. which have not been controlled and can not be removed due to multiple metastasis; * 3\. Known or self-reported HIV or syphilis infected persons; * 4\. Have participated in stem cell clinical research; * 5\. Pregnant or lactating women or those who have fertility plans in the past year; * 6\. The estimated life cycle is less than 48 hours; * 7\. Those who participated in other clinical trials within 3 months before screening; * 8\. Other conditions that the researcher thinks are not suitable for participating in the experiment.