Functional studies on the interaction between anti-PF4 antibodies and anticoagulants in vaccine-induced thrombotic thrombocytopenia

ABSTRACT

Background: With increasing number of vaccinations against SARS-CoV-2, rare but life threatening thrombotic events at unusual sites have been reported, and collectively this phenomenon is termed as vaccine-induced immune thrombotic thrombocytopenia (VITT). Pathophysiology of VITT is similar to that of heparin-induced thrombocytopenia (HIT), and associated with platelet-activating antibodies against platelet factor 4 (PF4). Aim(s) Current guidelines for anticoagulation in VITT patients are issued accordingly, with a focus on non-heparin anticoagulants. In this study, we investigated the interactions of heparin, danaparoid, fondaparinux and argatroban with VITT-Ab/ PF4 complexes. Method(s) We utilized an in-house enzyme immunoassays (EIA) to estimate antibody binding, inhibition and dissociation of preformed PF4-VITT complexes. Using biolayer interferometry (BLI), we analyzed binding kinetics and dissociation of complexes in real time. In a flow-based ex vivo model, we assessed the impact of anticoagulants on VITT-mediated thrombus formation. Result(s) We found that heparin and danaparoid not only inhibited VITT IgG binding to PF4 but were also able to effectively dissociate preformed PF4/IgG complexes in EIA. In BLI, binding of PF4 specific antibodies was observed for all VITT samples tested, and we found remarkable changes in their dissociation after addition of various anticoagulants. Furthermore, IgGs from VITT patients induce increased thrombus formation in comparison to the healthy controls (mean % SAC +/- SEM 11.59 +/- 0.57 vs. 1.99 +/- 0.34 respectively, p < 0.001), which can further be effectively inhibited with danaparoid and heparin (mean % SAC +/- SEM 2.82 +/- 0.50 and 1.85 +/- 0.56. p < 0.001). Fondaparinux and argatroban inhibited thrombus formation;however, they did not affect antibody binding. Conclusion(s) Taken together, our data shed a light on suitability of anticoagulants in VITT, and indicate that negatively charged anticoagulants can disrupt VITT-Ab/ PF4 interactions, which might serve as an approach to reduce antibody-mediated complications in VITT. Our results should be confirmed, however, in a clinical setting before a recommendation regarding the selection of anticoagulation in VITT patients could be made.