Background: During the course of COVID-19, the disease caused by the new coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), thrombotic phenomena and/or diffuse vascular damage are frequent, and viral elements have been observed within endothelial cells. Objectives: CD146 + circulating endothelial cells (CD146 + CECs) and their progenitors (CEPs) are increased in cardiovascular, thrombotic, infectious, and cancer diseases. The present study was designed to investigate their kinetics in novel coronavirus (COVID-19) patients. Methods: We used a validated flow cytometry procedure to enumerate viable and apoptotic CD146 + CECs and CEPs in COVID-19 patients during the course of the disease and in patients who recovered. Results: Viable CEPs per milliliter were significantly increased in COVID-19 patients compared with healthy controls. This increase was observed in patients with mild symptoms and not further augmented in patients with severe symptoms. In patients who recovered, CEPs decreased, but were in a range still significantly higher than normal controls. Regarding mature CD146 + CECs, in COVID-19 patients, their absolute number was similar to those observed in healthy controls, but the viable/apoptotic CD146 + CEC ratio was significantly different. Both mild and severe COVID-19 patients had significantly less apoptotic CD146 + CECs compared with healthy controls. Patients who recovered had significantly less CD146 + CECs per milliliter when compared with controls as well as to mild and severe COVID-19 patients. A positive correlation was found between the copies of SARS-CoV-2 RNA in the cellular fraction and apoptotic CEPs per milliliter in severe COVID-19 patients. Conclusions: CD146 + CECs and CEPs might be investigated as candidate biomarkers of endothelial damage in COVID-19 patients.

During the course of Covid-19, the disease caused by the new Coronavirus SARS-CoV-2, thrombotic phenomena and/or diffuse vascular damage are frequent, and viral elements have been observed within endothelial cells. Circulating endothelial cells (CECs) and their progenitors (CEPs) are increased in cardiovascular, thrombotic, infectious and cancer diseases. Using a validated flow cytometry procedure, we found that viable CEPs/mL were significantly increased in Covid-19 patients compared to healthy controls. This increase was observed in patients with mild symptoms and not further augmented in patients with severe symptoms. In patients who recovered, CEPs decreased, but were in a range still significantly higher than normal controls. Regarding mature CECs, in Covid-19 patients their absolute number was similar to those observed in healthy controls, but the viable/apoptotic CEC ratio was significantly different. Both mild and severe Covid-19 patients had significantly more viable CECs compared to healthy controls. Patients who recovered had significantly less CECs/mL when compared to controls as well as to mild and severe Covid-19 patients. A positive correlation was found between the copies of SARS-CoV-2 RNA in the cellular fraction and apoptotic CEPs/mL in severe Covid-19 patients. These findings suggest that CECs and CEPs might be investigated as candidate biomarkers of endothelial damage in Covid-19 patients.