SARS-CoV-2 hijacks neutralizing dimeric IgA for nasal infection and injury in Syrian hamsters.

ABSTRACT Prevention of robust severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection in nasal turbinate (NT) requires in vivo evaluation of IgA neutralizing antibodies. Here, we report the efficacy of receptor binding domain (RBD)-specific monomeric B8-mIgA1 and B8-mIgA2, and dimeric B8-dIgA1, B8-dIgA2 and TH335-dIgA1 against intranasal SARS-CoV-2 challenge in Syrian hamsters. These antibodies exhibited comparable neutralization potency against authentic virus by competing with human angiotensin converting enzyme-2 (ACE2) receptor for RBD binding. While reducing viral loads in lungs significantly, prophylactic intranasal B8-dIgA led to high amount of infectious viruses and extended damage in NT than controls. Mechanistically, while B8-dIgA failed inhibition of SARS-CoV-2 cell-to-cell transmission, virus might hijack B8-dIgA through dendritic cell-mediated trans-infection of NT epithelia with robust nasal infection. Cryo-EM further revealed B8 as a class II antibody binding trimeric RBDs in 3-up or 2-up/1-down conformation. Neutralizing dIgA, therefore, may engage an unexpected mode for SARS-CoV-2 nasal infection and injury.