Adenoviral Inciting Antigen and Somatic Hypermutation in VITT

Clinical Snapshot

Key Findings

• P Value: Not specified for primary associations

• Effect Size: Consistent molecular signature across all analysed VITT cases

• Primary Outcome: Shared IGLV3-21*02 or *03 allele with critical K31E somatic hypermutation in VITT patients

• Nnt Or Sensitivity: Cross-reactive antibodies specifically bound adenoviral protein VII linear epitope

• Confidence Interval: Not reported

Clinical Application

Findings may inform risk stratification and vaccine selection, though genetic testing not currently routine Highly relevant given widespread use of ChAdOx1 (AstraZeneca) vaccine in Australia and TGA safety monitoring requirements Individuals receiving adenoviral vector COVID-19 vaccines, particularly those with IGLV3-21*02/03 alleles

Abstract

BACKGROUND: Vaccine-induced immune thrombocytopenia and thrombosis (VITT) is a rare prothrombotic complication that occurs after adenoviral vector-based vaccination against coronavirus disease 2019; in rare cases, it can also occur after natural adenovirus infection. VITT is mediated by platelet-activating antibodies against the highly cationic protein platelet factor 4 (PF4). The underlying inciting antigen trigger and immunopathogenesis remain unknown. METHODS: We used antibody proteomics to determine the amino acid sequences of anti-PF4 antibodies from 21 patients with VITT and sequenced the genes encoding the immunoglobulin light-chain hypervariable region from 100 patients with VITT. To identify an adenoviral trigger, we used the antigen-binding fingerprints of anti-PF4 and anti-adenovirus protein antibodies to identify a shared serum clonotype and subsequently used adenovirus protein peptides and recombinant anti-PF4 VITT antibodies to map the mimicking linear epitope. RESULTS: Genomic and proteomic profiling of VITT antibodies revealed a shared immunoglobulin light-chain allele, IGLV3-21*02 or *03, harboring a critical somatic hypermutation, K31E. Only antibodies purified against adenoviral core protein VII (pVII) contained anti-PF4 species matching the VITT fingerprint; antibodies against intact virions or other adenoviral proteins did not. Cross-reactive IgGs were mapped to a basic linear epitope on pVII. A pathogenic anti-PF4 VITT antibody, back-mutated to germline (K31), lost its prothrombotic activity in vitro and in vivo and preferentially bound pVII, a finding that directly supported the role of the hypermutation in the antigenic shift from adenovirus pVII to PF4. CONCLUSIONS: The results of our study indicate that VITT occurs when, in persons with immunoglobulin light-chain allele IGLV3-21*02 or *03, a specific somatic hypermutation develops that affects antibodies that recognize a specific epitope on the adenoviral core protein pVII, which results in misdirection of antibody targeting toward PF4. (Funded by Deutsche Forschungsgemeinschaft and others; German Clinical Trials Register number, DRKS00025738; EU Post-Authorization Study Register number, EUPAS45098.).

References

1. 1.Wang, J. J., Schönborn, L., Warkentin, T. E., Müller, L., Thiele, T., Ulm, L., Völker, U., Ameling, S., Franzenburg, S., Kaderali, L., Tzvetkova, A., Colella, A., Chataway, T., Tan, C. W., Armour, B., Troelnikov, A., Rutten, L., McCluskey, J., Zahn, R., Gordon, T. P., & Greinacher, A. (2026). Adenoviral inciting antigen and somatic hypermutation in VITT. New England Journal of Medicine. https://doi.org/10.1093/nar/28.1.214