CD39 polymorphism enables lung thrombosis in sickle cell disease

Sickle cell disease (SCD) is the most common monogenic-hemolytic disorder affecting people of African ancestry. Adenosine diphosphate (ADP) released following intravascular hemolysis activates platelets by stimulating purinergic receptors to promote thrombosis. Despite brisk intravascular hemolysis, which releases high levels of ADP into plasma, and evidence of platelet and hemostatic activation, it remains elusive why only a subset of SCD patients develop lung thrombosis. Using real-time in vivo lung microscopy, we report a surprising finding that humanized SCD mice are protected from ADP-induced lung thrombosis, which is secondary to the degradation of ADP by CD39 present in circulating extracellular vesicles released by the lung endothelium. ADP-induced platelet aggregation is also impaired in the blood of SCD patients with elevated levels of CD39⁺ extracellular vesicles. CD39 polymorphism rs3176891A→G is associated with the incidence of lung thrombosis in SCD patients but not healthy humans of African ancestry. Remarkably, CD39⁺ extracellular vesicles are fewer and ADP-induced platelet aggregation is higher in the blood of SCD patients with rs3176891G allele. This study identifies a novel extracellular vesicle-dependent mechanism preventing lung thrombosis in SCD and reveals how CD39 polymorphisms may impair this protection to increase the risk for lung thrombosis in a subset of SCD patients.