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.