This is phase II study to assess the efficacy of NestaCell® (mesenchymal stem cell) to treat severe COVID-19 pneumonia.

The number of infections of COVID-19 worldwide has killed thousands and is continually rising. The novel coronavirus attacks the human body by attaching to the angiotensin-converting enzyme-2 (ACE2), a protective enzyme against lung damage. In addition, the cellular serine protease TMPRSS2 for HCoV-19 Spike protein priming is also essential for the host cell entry and spread. Coronaviruses can be deadly, in large part because they cause "cytokine storms." These storms result from imbalances between pro-inflammatory and anti-inflammatory proteins called cytokines, which can cause extreme inflammation and respiratory complications. Respiratory distress kills hundreds of thousands of people each year worldwide, and hundreds of clinical trials are testing drugs to treat it.

MSCs have been widely used in cell-based therapy, from basic research to clinical trials Safety and effectiveness have been clearly documented in many clinical trials, especially in the immune-mediated inflammatory diseases.

NestaCell® is a mesenchymal stem cell therapy produced by Cellavita and proved to be safe in previous clinical trials.

The aim of this study is assess the efficacy of NestCell® as an add-on therapy to standard treatment to treat patients with severe COVID-19 pneumonia. .

Patients included will be randomized to receive 2x10^7 cells (20 million cells) on days 1, 3, 5 and 7.

Inclusion Criteria:

1. Male or female, aged ≥ 18 years 2. Present a confirmed or pending diagnosis of COVID-19, but with tomographic and clinical signs strongly suggestive of SARS-CoV-2 infection (COVID-19), with pulmonary impairment greater than or equal to 50% and: i. Oxygen saturation <95%; ii. CURB-65 rating ≥ a 4; d) Participants with a score on WHO ordinal scale that measures illness severity over time equal to 5 (Hospitalized with non-invasive ventilation or high-flow oxygen).

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. Other conditions that the researcher thinks are not suitable for participating in the experiment.
8. Shock
9. Continuous use of immunosuppressive agents or organ transplants in the past 6 months;

It is believed that after the data analysis and presentation to the National Commission on Research Ethics, all data of the study will become public.