Insights in ChAdOx1 nCoV-19 vaccine-induced immune thrombotic thrombocytopenia

Blood. 2021 Dec 2;138(22):2256-2268. doi: 10.1182/blood.2021013231.


SARS-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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenoviridae / immunology
  • Animals
  • Antigen-Antibody Complex / immunology*
  • Antigen-Antibody Complex / ultrastructure
  • Autoantibodies / biosynthesis
  • Autoantibodies / immunology*
  • COVID-19 / prevention & control*
  • Capillary Leak Syndrome / etiology
  • Capsid Proteins / adverse effects*
  • Capsid Proteins / immunology
  • Cell Line, Transformed
  • ChAdOx1 nCoV-19 / adverse effects*
  • ChAdOx1 nCoV-19 / chemistry
  • ChAdOx1 nCoV-19 / immunology
  • ChAdOx1 nCoV-19 / toxicity
  • Drug Contamination*
  • Dynamic Light Scattering
  • Epitopes / chemistry
  • Epitopes / immunology
  • Extracellular Traps / immunology
  • Extravasation of Diagnostic and Therapeutic Materials / etiology
  • Genetic Vectors / adverse effects*
  • Genetic Vectors / immunology
  • HEK293 Cells / chemistry
  • HEK293 Cells / immunology*
  • Humans
  • Imaging, Three-Dimensional
  • Immunoglobulin G / biosynthesis
  • Immunoglobulin G / immunology*
  • Inflammation
  • Mice
  • Microscopy / methods
  • Platelet Activation
  • Platelet Factor 4 / immunology*
  • Proteomics
  • Purpura, Thrombocytopenic, Idiopathic / blood
  • Purpura, Thrombocytopenic, Idiopathic / etiology*
  • Purpura, Thrombocytopenic, Idiopathic / immunology
  • SARS-CoV-2*
  • Sinus Thrombosis, Intracranial / diagnostic imaging
  • Sinus Thrombosis, Intracranial / immunology
  • Spike Glycoprotein, Coronavirus / adverse effects*
  • Spike Glycoprotein, Coronavirus / immunology
  • Virus Cultivation


  • Antigen-Antibody Complex
  • Autoantibodies
  • Capsid Proteins
  • Epitopes
  • Immunoglobulin G
  • PF4 protein, human
  • Spike Glycoprotein, Coronavirus
  • spike protein, SARS-CoV-2
  • Platelet Factor 4
  • ChAdOx1 nCoV-19