ChAdOx1 interacts with CAR and PF4 with implications for thrombosis with thrombocytopenia syndrome

Abstract

Vaccines derived from chimpanzee adenovirus Y25 (ChAdOx1), human adenovirus type 26 (HAdV-D26), and human adenovirus type 5 (HAdV-C5) are critical in combatting the severe acute respiratory coronavirus 2 (SARS-CoV-2) pandemic. As part of the largest vaccination campaign in history, ultrarare side effects not seen in phase 3 trials, including thrombosis with thrombocytopenia syndrome (TTS), a rare condition resembling heparin-induced thrombocytopenia (HIT), have been observed. This study demonstrates that all three adenoviruses deployed as vaccination vectors versus SARS-CoV-2 bind to platelet factor 4 (PF4), a protein implicated in the pathogenesis of HIT. We have determined the structure of the ChAdOx1 viral vector and used it in state-of-the-art computational simulations to demonstrate an electrostatic interaction mechanism with PF4, which was confirmed experimentally by surface plasmon resonance. These data confirm that PF4 is capable of forming stable complexes with clinically relevant adenoviruses, an important step in unraveling the mechanisms underlying TTS.

Pathogenesis of vaccine-induced immune thrombotic thrombocytopenia (VITT)

“…A major strength of this study is that the biophysical assessment and Brownian dynamics simulation identified potential binding sites of PF4 on the virus surface ( Figure 1 ). In this study, binding of PF4 to adenovirus occured with low affinity (Kd 300 nmol) [16] . This is much lower than the interaction forces of PF4 with polyanions exposing the epitope to which antibodies characteristic for heparin-induced thrombocytopenia (HIT) bind [12] .…”

“…PF4 also binds to adenovirus [14] , [15] . Baker et al 2021 [16] determined the structure of the ChAdOx1 viral vector and demonstrated an electrostatic interaction mechanism with PF4. They confirmed binding of PF4 to adenovirus using a technique known as plasmon resonance.…”

Immune-Mediated Platelet Activation in COVID-19 and Vaccine-Induced Immune Thrombotic Thrombocytopenia

“…An electrostatic interaction mechanism between PF4 and ChAdOx1 nCov19 viral vector was determined using computational simulations, and later confirmed experimentally by surface plasmon resonance. This study hints toward the direct involvement of vector adenovirus, forming stable complexes with PF4 and subsequent pathogenesis in VITT (67). Henceforth the binding of PF4 with the viral capsid might create a novel antigen, which is subsequently taken up by monocytes and trafficked to lymph nodes, where it stimulates proliferation of anti-PF4 memory B cells.…”

Refined Capsid Structure of Human Adenovirus D26 at 3.4 Å Resolution

“…While this COVID-19 vaccine has been injected intramuscularly, some fraction of injected vaccine will leak into the blood, thereby potentially inducing effects on the clotting system. Similar to most interactions of Ad26 with receptors and proteins, the binding of blood clotting factor, platelet factor 4 (PF4), also has a low affinity with binding constants for chimpanzee adenovirus vector (ChAdOx1), Ad5, and Ad26 of 0.661, 0.789, and 0.301 µM, respectively [56]. This binding has a 1000-fold lower affinity than the 0.000229 µM binding of FX to Ad5 [37].…”