Intramuscularly administered vaccines stimulate robust serum neutralizing antibodies, yet they are often less competent in eliciting sustainable “sterilizing immunity” at the mucosal level. Our study uncovers a strong temporary neutralizing mucosal component of immunity, emanating from intramuscular administration of an mRNA vaccine. We show that saliva of BNT162b2 vaccinees contains temporary IgA targeting the receptor-binding domain (RBD) of severe acute respiratory syndrome coronavirus-2 spike protein and demonstrate that these IgAs mediate neutralization. RBD-targeting IgAs were found to associate with the secretory component, indicating their bona fide transcytotic origin and their polymeric multivalent nature. The mechanistic understanding of the high neutralizing activity provided by mucosal IgA, acting at the first line of defense, will advance vaccination design and surveillance principles and may point to novel treatment approaches and new routes of vaccine administration and boosting.

Intramuscularly administered vaccines stimulate robust serum neutralizing antibodies, yet they are often less competent in eliciting sustainable 'sterilizing immunity' at the mucosal level. Our study uncovers, strong neutralizing mucosal component (NT50 ≤ 50pM), emanating from intramuscular administration of an mRNA vaccine. We show that saliva of BNT162b2 vaccinees contains temporary IgA targeting the Receptor-Binding-Domain (RBD) of SARS-CoV-2 spike protein and demonstrate that these IgAs are key mediators of potent neutralization. RBD-targeting IgAs were found to associate with the Secretory Component, indicating their bona-fide transcytotic origin and their dimeric tetravalent nature. The mechanistic understanding of the exceptionally high neutralizing activity provided by mucosal IgA, acting at the first line of defence, will advance vaccination design and surveillance principles, pointing to novel treatment approaches, and to new routes of vaccine administration and boosting.

No abstract

Negeviruses (NVs) are a recently discovered taxon of enveloped, positive sense, single-stranded RNA viruses, infecting blood-sucking insects. While classical arthropod-borne (arbo)viruses like dengue and Chikungunya infect both insects and vertebrates, NVs are restricted to insects and do not have any known vertebrate host and are thus classified as insect-restricted viruses. Previous works have predicted a structure consisting of three ORFs, the first with homologous regions to RNA-dependent RNA polymerase, helicase, and methyl transferases in plant viruses. On the contrary, ORF2 and ORF3 do not have homologs and are predicted to encode membrane glycoproteins. Their structures, functions, and significance remain vague. We focus on the characterization of the viral proteins, structural organization of the virion, and the principles of their interaction with the host cell. We purified the virion particles of Negev virus produced in mosquito cells and identified its structural components. In addition, we cloned and overexpressed ORF2 and ORF3 of Negeviruses. Furthermore, we defined and successfully produced and purified recombinant ORF2. Subsequent characterization using gel filtration, ion exchange, and MALS techniques revealed that the ORF2 of Negeviruses exhibit different higher order assembly patterns: dimerization and multimerization in a concentration- and pH-dependent manner that correspond to their biological role. We combine biochemical, structural and cell biology techniques to unravel mechanisms of Negev virus interaction with the host cell.