Table 2.
Criteria of the literature search
| Electronic databases | |
| PubMed/MEDLINE, Scopus, Cochrane Collaboration, Web of Science | |
| Publications | |
| Language | English |
| Period of time | 1 January 1970–31 July 2022 |
| Subject | Human clinical studies |
| Setting | Hospital wards and intensive care units |
| Included study type | Randomized double-blind placebo-controlled clinical trials on the use of investigational therapy in addition to recommended/standard therapy (add-on therapy) |
| Randomized open-label placebo-controlled clinical trial on the use of investigational therapy in addition to recommended/standard therapy (add-on therapy) | |
| Nonrandomized open-label parallel-group clinical trial on the use of investigational therapy in addition to recommended/standard therapy (add-on therapy) | |
| Prospective single-arm study on the use of investigational therapy when recommended/standard therapy has failed | |
| Excluded publications | |
| Any prospective study on the use of investigational therapy in stable patients on recommended/standard therapy | |
| Any study on the use of investigational therapy as add-on therapy if recommended/standard therapy was not described | |
| Any study on the use of investigational therapy as add-on therapy, or when recommended/standard therapy has failed, if recommended/standard therapy did not include antivirals, glucocorticoids, or immunomodulators, singly or in combination | |
| Retrospective studies | |
| Case series | |
| Case report | |
| Articles posted on pre-print servers | |
| Abstracts | |
| Conference proceeding | |
| Opinion article | |
| Review articles | |
| Editorials | |
| Theses | |
| Book chapters | |
| Keywords | |
| Mesenchymal stem cells | |
| Mesenchymal stromal cells | |
| Exosomes | |
| Extracellular vesicles | |
| Pneumonia | |
| Acute respiratory distress syndrome | |
| Cytokine storm | |
| Systemic inflammation | |
| Coronavirus | |
| COVID-19 | |
| Influenza | |
COVID-19 coronavirus disease 2019, IT investigational therapy