Mesenchymal stromal cell secretome reduces lung injury and thrombo-inflammation induced by SARS-CoV-2 spike protein

Severe COVID-19 is characterized by thrombo-inflammatory processes within the lung microvasculature. In pursuit of effective treatments, clinical studies explored mesenchymal stromal cells (MSCs) as a promising approach due to their anti-inflammatory, immunomodulatory, and regenerative properties, through their paracrine action.Here, we tested the conditioned medium (CM) derived from human umbilical cord (UC)-MSCs in acute lung injury induced by the spike protein subunit 1 (S1) in ACE2-humanized male mice. Injection of CM significantly limited S1-induced lung injury, edema, and fibrosis. This was associated with reduced vascular dysfunction, in terms of restored thrombomodulin levels and decreased von Willebrand (vWF) expression. By preserving endothelial glycocalyx, CM reduced complement C3 accumulation, favoring factor H binding on the lung microvasculature. Reduced oxidative stress, nuclear NF-κB p65 accumulation, and inflammatory cell infiltration were also observed in response to CM in S1-injected mice.In vitro, CM counteracted thrombo-inflammation by preserving thrombomodulin, as well as limiting vWF expression, due to endothelial glycocalyx recovery. CM reduced nuclear translocation of NF-κB p65 and its downstream targets, ICAM-1 and P-selectin, translating in decreased C3 deposits, platelet aggregation, and leukocyte adhesion on S1-challenged endothelial cells.Collectively, these data indicate that UC-MSC-derived secretome represents a promising therapy in COVID-19 due to its potent anti-thrombotic and anti-inflammatory effects on lung microcirculation.