Abstract
AbstractSARS-CoV-2 vaccine ChAdOx1 nCoV-19 (AstraZeneca) causes a thromboembolic complication termed vaccine-induced immune thrombotic thrombocytopenia (VITT). Using biophysical techniques, mouse models, and analysis of VITT patient samples, we identified determinants of this vaccine-induced adverse reaction. Super-resolution microscopy visualized vaccine components forming antigenic complexes with platelet factor 4 (PF4) on platelet surfaces to which anti-PF4 antibodies obtained from VITT patients bound. PF4/vaccine complex formation was charge-driven and increased by addition of DNA. Proteomics identified substantial amounts of virus production-derived T-REx HEK293 proteins in the ethylenediaminetetraacetic acid (EDTA)-containing vaccine. Injected vaccine increased vascular leakage in mice, leading to systemic dissemination of vaccine components known to stimulate immune responses. Together, PF4/vaccine complex formation and the vaccine-stimulated proinflammatory milieu trigger a pronounced B-cell response that results in the formation of high-avidity anti-PF4 antibodies in VITT patients. The resulting high-titer anti-PF4 antibodies potently activated platelets in the presence of PF4 or DNA and polyphosphate polyanions. Anti-PF4 VITT patient antibodies also stimulated neutrophils to release neutrophil extracellular traps (NETs) in a platelet PF4-dependent manner. Biomarkers of procoagulant NETs were elevated in VITT patient serum, and NETs were visualized in abundance by immunohistochemistry in cerebral vein thrombi obtained from VITT patients. Together, vaccine-induced PF4/adenovirus aggregates and proinflammatory reactions stimulate pathologic anti-PF4 antibody production that drives thrombosis in VITT. The data support a 2-step mechanism underlying VITT that resembles the pathogenesis of (autoimmune) heparin-induced thrombocytopenia.
Highlights
Vaccination against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is an important countermeasure to fight the ongoing COVID-19 pandemic
These interactions led to complexes comprised of vaccine particles and platelet factor 4 (PF4) to which vaccine-induced immune thrombotic thrombocytopenia” (VITT) patient-derived anti-PF4 immunoglobulin G (IgG) bound on platelet surfaces (Figure 1A, right panel)
Quantification of the components of the particles revealed that 45% contained ternary complexes of PF4, AV hexon proteins, and anti-PF4 antibodies, whereas 50% were positive for PF4/AV hexon protein or PF4/anti-PF4 antibody complexes only (Figure 1B)
Summary
Vaccination against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is an important countermeasure to fight the ongoing COVID-19 pandemic. Beginning in March 2021, cerebral venous sinus thrombosis (CVST), splanchnic vein thrombosis, and other unusual severe thrombotic events in combination with thrombocytopenia were reported in otherwise healthy individuals beginning 5 to 20 days following ChAdOx1 nCoV-19 vaccination. This novel disorder, “vaccine-induced immune thrombotic thrombocytopenia” (VITT; synonym, thrombosis with thrombocytopenia syndrome), has been associated with high-titer immunoglobulin G (IgG) class antibodies directed against the cationic platelet chemokine, platelet factor 4 (PF4).[2] Anti-PF4 antibodies potently activate platelets with platelet activation greatly enhanced by PF4.2,3 Pathologic anti-PF4 antibodies were infrequently found in CVST patients prior to VITT, suggesting that the vaccineinduced antibodies drive these thrombotic complications.[4]
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