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Biophysical studies do not reveal direct interactions between human PF4 and Ad26.COV2.S vaccine

Marijn van der Neut Kolfschoten¹, Hanna Inganäs¹, Clara Perez-Peinado¹

¹Janssen Vaccines & Prevention B.V., Leiden, South Holland, The Netherlands.

Journal of Thrombosis and Haemostasis : JTH

|December 30, 2023

Abstract

Background:

COVID-19 vaccines have been widely used to control the SARS-CoV-2 pandemic. In individuals receiving replication-incompetent, adenovirus vector-based COVID-19 vaccines (eg, ChAdOx1 nCoV-19 [AstraZeneca] or Ad26.COV2.S [Johnson & Johnson/Janssen] vaccines), a very rare but serious adverse reaction has been reported and described as vaccine-induced immune thrombotic thrombocytopenia (VITT). The exact mechanism of VITT following Ad26.COV2.S vaccination is under investigation. Antibodies directed against human platelet factor 4 (PF4) are considered critical in the pathogenesis of VITT, suggesting similarities with heparin-induced thrombocytopenia. It has been postulated that components of these vaccines mimic the role of heparin by binding to PF4, triggering production of these anti-PF4 antibodies.

Objectives:

This study aimed to investigate the potential interaction between human PF4 and Ad26.COV2.S vaccine using several biophysical techniques.

Methods:

Direct interaction of PF4 with Ad26.COV2.S vaccine was investigated using dynamic light scattering, biolayer interferometry, and surface plasmon resonance. For both biosensing methods, the Ad26.COV2.S vaccine was immobilized to the sensor surface and PF4 was used as analyte.

Results:

No direct interactions between PF4 and Ad26.COV2.S vaccine could be detected using dynamic light scattering and biolayer interferometry. Surface plasmon resonance technology was shown to be unsuitable to investigate these types of interactions.

Conclusion:

Our findings make it very unlikely that direct binding of PF4 to Ad26.COV2.S vaccine or components thereof is driving the onset of VITT, although the occurrence of such interactions after immunization (potentially facilitated by unknown plasma or cellular factors) cannot be excluded. Further research is warranted to improve the understanding of the full mechanism of this adverse reaction.

Insights

This study investigated if the Ad26.COV2.S COVID-19 vaccine directly binds to human platelet factor 4 (PF4). Researchers found no direct interaction, making this mechanism unlikely for vaccine-induced immune thrombotic thrombocytopenia (VITT).

Area of Science:

Immunology
Vaccinology
Biophysics

Background:

Adenovirus vector-based COVID-19 vaccines, such as Ad26.COV2.S, have been linked to rare cases of vaccine-induced immune thrombotic thrombocytopenia (VITT).
VITT pathogenesis is thought to involve antibodies against human platelet factor 4 (PF4), similar to heparin-induced thrombocytopenia.
It is hypothesized that vaccine components may bind to PF4, initiating an immune response.

Purpose of the Study:

To investigate the direct interaction between human PF4 and the Ad26.COV2.S vaccine.
To explore potential biophysical mechanisms underlying VITT following Ad26.COV2.S vaccination.

Main Methods:

Utilized dynamic light scattering, biolayer interferometry, and surface plasmon resonance to assess PF4-vaccine interactions.
Immobilized the Ad26.COV2.S vaccine onto sensor surfaces for analysis with PF4 as the analyte.

Main Results:

Dynamic light scattering and biolayer interferometry detected no direct binding between PF4 and the Ad26.COV2.S vaccine.
Surface plasmon resonance proved unsuitable for evaluating these specific molecular interactions.

Conclusions:

Direct PF4 binding to the Ad26.COV2.S vaccine is unlikely to be the primary cause of VITT.
The possibility of indirect interactions or interactions facilitated by other factors post-vaccination cannot be ruled out.
Further research is necessary to fully elucidate the mechanisms of VITT.

Read full analysis

Keywords:

Ad26.COV2.S COVID-19 vaccines PF4 SARS-CoV-2 VITT

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