Thread by @Siegerist

Vector-based SARS-CoV2 #vaccines have been associated with vaccine-induced thrombotic thrombocytopenia #VITT/#TTS. It is known that similar to HIT, anti-PF4 antibodies are formed which activate platelets therefore eventually leading to serious thrombosis: nature.com/articles/s4158…

This serious and sometimes fatal condition has been described for both vector-based SARS-CoV2 vaccines ChAdOx1 nCoV-19 (AstraZeneca) and in less frequency for Ad26.COV2.S (Johnson&Johnson). However, it is still unclear why there are large differences in the incidence of #VITT.

To tackle this question, we dropped everything else and compared both vaccines in our local, highly interdisciplinary multi-expertise group from @uni_greifswald, @UMGreifswald and @Loeffler_News: #GreifswalderForscher

#Proteomics (SDS-PAGE, WB, LC-MS/MS) showed that in direct comparison to Ad26.COV2.S, ChAdOx1 nCoV-19 contained larger amounts of host-cell proteins from production in human cell lines.

As #VITT involves high-affinity anti-PF4 antibodies, likely due to the formation of an immunogenic neo-epitope with PF4 and vaccine components, we focused on interaction studies of the vaccines with PF4.

Using electron microscopy and biophysical methods like dynamic light scattering, we learned that size-increasing complexes formed in ChAdOx nCoV-19, but not Ad26.COV2.S upon incubation with PF4 @palankarr

We then used #superresolution single-molecule localization microscopy (#dSTORM) and dual-labeled the vector capsid and PF4. We could confirm that indeed, PF4-complexes formed in close vicinity to ChAdOx1 nCoV-19 but not Ad26.COV2.S vaccine constituents.

Interestingly, PF4-affinity was largely decreased when we purified ChAdOx1 nCoV-19 virions from the vaccine, indicating that this direct interaction is mediated or increased by another vaccine component like free protein.

Summarized, our work shows that besides using different vectors, there are pronounced differences in the composition and PF4 affinity of ChAdOx1 nCoV-19 and Ad26.COV2.S which could be a possible explanation for different #VITT incidence rates.

Find the full preprint I, together with @palankarr @palankarr and two other colleagues (not on Twitter) co-first authored here. Feel free to comment on the preprint! researchsquare.com/article/rs-736…

Additionally, when we intramuscularly injected the vaccines in transgenic #zebrafish expressing a 78kDa GFP-tagged plasma protein, we found that ChAdOx1 nCoV-19 rapidly increases vascular permeability.