Abstract

Abstract The severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) causes coronavirus disease 2019 (COVID‐19) and has been related to more than 7 million deaths globally since 2019. The association of high levels of IL‐6 with severe cases led to the early evaluation of the anti‐IL6 inhibitor tocilizumab as a potential treatment, which unfortunately failed to improve survival in many trials. Moreover, little is known about the development of COVID‐19 sequelae, and biomarkers are needed to understand and anticipate these processes. Because extracellular vesicles (EVs) play an important role in viral infection and immune response, they could potentially serve as predictive and prognostic biomarkers. We isolated EVs from 39 patients with severe COVID‐19, from which 29 received tocilizumab and 10 were considered controls. Blood samples, which were collected at hospitalisation before treatment, at Day 7, and Day 15 during follow‐up, were assessed by immunoblot for longitudinal expression of spike (S) and nucleocapsid (N) proteins. Dynamic expression was calculated and compared with clinicopathological and experimental variables. Expression of EV S was validated by immunogold and imaging flow‐cytometry, revealing an enrichment in CD9+ EVs. As a result, decreasing expression of EV viral proteins was observed in patients treated with tocilizumab. Moreover, higher increase in EV S was observed in patients with lower antibody response, hyperfibrinogenemia, lower respiratory function, higher blood pressure and shorter outcomes. These findings lay the foundation for future studies characterizing the role of EVs in multiorgan assessment and identifying biomarkers in patients with severe COVID‐19 and possible long COVID.