Enhanced adenoviral reactivity in Guillain-Barré syndrome after SARS-CoV-2 infection and vaccination

Case reports and series suggested an association between SARS-CoV-2 and Guillain-Barré syndrome (GBS). However, the GBS epidemic which was predicted from early risk estimates did not materialise in overall case numbers, and no plausible mechanism for any link has been established. An increased risk of GBS following adenoviral vector-based COVID-19 vaccination has been more consistently demonstrated, but a pathophysiological explanation for this association has also not yet emerged. Here, we sought to identify whether patients with GBS following COVID-19 infection or vaccination had any distinct clinical or serological features differentiating them from one another or non-pandemic GBS, and to explore the potential mechanisms of any associations. Between March 2020 and October 2021, sera from patients with GBS (n=64) and controls (n=70) were collected. Clinical features were retrieved from medical records. GBS cases were evaluated for diagnostic certainty by Brighton criteria and classified as non-COVID-19 associated (GBS-NC, n=20), GBS after COVID-19 infection (GBS-AC, n=10), or GBS after COVID-19 vaccination (GBS-AV, n=34). The humoral responses to SARS-CoV-2 proteins and putative peripheral nerve antigens, and the cytokine profile of each group were established and compared. Antibodies cloned from the acute-phase plasmablasts of an individual with GBS-AC were also assessed for reactivity against SARS-CoV-2 and peripheral nerve antigens. Sera from GBS patients and from individuals who received COVID-19 vaccinations (n=36: 16 ChAdOx1, 10 Ad26.COV2.S/Janssen, and 10 Tozinameran/Pfizer–BioNTech) without developing GBS were tested for IgG reactivity against SARS-CoV-2 and adenoviral proteins. There were no clinical differences between the GBS groups. Patients with GBS-AC had a greater IgG reactivity to the S1 component of the SARS-CoV-2 spike protein compared to non-GBS COVID-19 controls. A minority of antibodies from cloned plasmablasts targeted SARS-CoV-2 proteins but there was no reactivity or cross reactivity with peripheral nerve antigens or tissue. There were no other serological or immunological differences between the GBS groups. However, when compared to uncomplicated vaccine recipients, GBS patients in toto, and each group individually, demonstrated significantly greater antibody reaction to a range of human adenoviral proteins. Compared to controls exposed to the same immunological stimulus, antibody reactivities to viral antigens are enhanced in patients with GBS. However, we found no mechanistic link between S1 and peripheral nerve reactivity or pathology. Serological responses to adenoviral proteins may be directly involved in the pathogenesis of Guillain-Barré syndrome, potentially contributing to cases with currently unexplained aetiology.