Rationale: The coronavirus disease (COVID-19) pandemic is now a global health concern. Objectives: We compared the clinical characteristics, laboratory examinations, computed tomography images, and treatments of patients with COVID-19 from three different cities in China. Methods: A total of 476 patients were recruited from January 1, 2020, to February 15, 2020, at three hospitals in Wuhan, Shanghai, and Anhui. The patients were divided into four groups according to age and into three groups (moderate, severe, and critical) according to the fifth edition of the Guidelines on the Diagnosis and Treatment of COVID-19 issued by the National Health Commission of China. Measurements and Main Results: The incidence of comorbidities was higher in the severe (46.3%) and critical (67.1%) groups than in the moderate group (37.8%). More patients were taking angiotensinconverting enzyme inhibitors/angiotensin II receptor blockers in the moderate group than in the severe and critical groups. More patients had multiple lung lobe involvement and pleural effusion in the critical group than in the moderate group. More patients received antiviral agents within the first 4 days in the moderate group than in the severe group, and more patients received antibiotics and corticosteroids in the critical and severe groups. Patients .75 years old had a significantly lower survival rate than younger patients. Conclusions: Multiple organ dysfunction and impaired immune function were the typical characteristics of patients with severe or critical illness. There was a significant difference in the use of angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers among patients with different severities of disease. Involvement of multiple lung lobes and pleural effusion were associated with the severity of COVID-19. Advanced age (>75 yr) was a risk factor for mortality.

Mesenchymal stromal cell‐derived extracellular vesicles (MSC‐EVs) turn out to be a promising source of cell‐free therapy. Here, we investigated the biodistribution and effect of nebulized human adipose‐derived MSC‐EVs (haMSC‐EVs) in the preclinical lung injury model and explored the safety of nebulized haMSC‐EVs in healthy volunteers. DiR‐labelled haMSC‐EVs were used to explore the distribution of nebulized haMSC‐EVs in the murine model. Pseudomonas aeruginosa‐induced murine lung injury model was established, and survival rate, as well as WBC counts, histology, IL‐6, TNF‐α and IL‐10 levels in bronchoalveolar lavage fluid (BALF) were measured to explore the optimal therapeutic dose of haMSC‐EVs through the nebulized route. Twenty‐four healthy volunteers were involved and received the haMSC‐EVs once, ranging from 2 × 108 particles to 16 × 108 particles (MEXVT study, NCT04313647). Nebulizing haMSC‐EVs improved survival rate to 80% at 96 h in P. aeruginosa‐induced murine lung injury model by decreasing lung inflammation and histological severity. All volunteers tolerated the haMSC‐EVs nebulization well, and no serious adverse events were observed from starting nebulization to the 7th day after nebulization. These findings suggest that nebulized haMSC‐EVs could be a promising therapeutic strategy, offering preliminary evidence to promote the future clinical applications of nebulized haMSC‐EVs in lung injury diseases.

Ad-MSC derived EVs contain high level of miR-466. Both Ad-MSCs and Ad-MSC EVs have therapeutic effects in treating MDR-PA-induced pneumonia. miR-466 promotes phenotype switch to M2 type of macrophages, exerting immunomodulatory effects.