Thrombotic Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination
Kang-Yiu Lai, Shek-Yin Au, Ka-Man Fong
Abstract
Thrombotic Thrombocytopenia after ChAdOx1 nCoV-19 VaccinationTo the Editor: Greinacher et al. (April 9) 1 report on the development of platelet-activating antibodies against platelet factor 4 (PF4) after ChAdOx1 nCoV-19 vaccination in patients without previous exposure to heparin.These patients had clinical features that mimicked autoimmune heparininduced thrombocytopenia.In serum samples obtained from these patients, platelets were shown to be activated in the absence of heparin.Platelet activation was shown to be inhibited when high doses of heparin were added to the serum samples.Thrombocytopenia after the administration of adenoviral gene transfer vectors has been reported.Platelet activation with the formation of adenovirus-platelet-leukocyte complexes leading to accelerated platelet clearance in the liver and thrombocytopenia is common after adenovirus administration.P-selectin and von Willebrand factor are critically involved in a complex interplay between platelets, leukocytes, and endothelium in mediating accelerated platelet clearance. 2,3hese adenovirus-platelet-leukocyte complexes are then taken up by the liver through interaction with membrane-associated heparan sulfate proteoglycans, which act as receptors for viral entry. 4 Heparin can lead to dose-dependent inhibition of this interaction. 5Perhaps the interaction with heparan sulfate may sensitize the body to the development of platelet-activating antibodies against PF4 and lead to heparin-induced thrombocytopenia and thrombosis.