Synthetically engineered IgG1 antibody Fc fragments presenting influenza A virus receptor sialic acid inhibit viral haemagglutination activity, but enhance virus replication in cultured A549 cells (preprint)

Many clinically important viruses, including influenza A, SARS-CoV-1, adenoviruses, and DNA tumour viruses such as Kaposi’s sarcoma herpesvirus use multivalent binding to sialic acid (SA) to infect cells, or to modulate immune responses through interactions with sialylated attachment factors that facilitate virus infectivity and/or host survival. Molecular scaffolds rich in SA that bind virions with high avidity may therefore be useful as anti-infective medicines. We generated a panel of 12 of these molecules using fragment-crystallisable scaffolds in CHO-S cells that are rich in SA. The viral surface protein of influenza A virus (IAV), haemagglutinin, binds SA for cell entry, and so we tested the activity of these compounds against this virus. Two of the sialylated Fc-molecules reduced IAV haemagglutination activity by up to 64-fold. However, the same molecules enhanced virus infectivity of A549 cultured cells. To explain the increased viral titres, we postulated that sialylated Fcs may be anti-inflammatory. However, sialylated Fc multimers were instead pro-inflammatory; they induced chemokine/cytokine responses from differentiated human THP-1 derived macrophages, including raised IL-8 and MIP-1α/β, that mimicked responses driven by universal type I interferon. Steric targeting of SA to block virus entry may therefore have unexpected effects in target cells that currently preclude their use for medical intervention.

Engineering a Vaccine Platform using Rotavirus A to Express SARS-CoV-2 Spike Epitopes (preprint)

Human rotavirus (RV) vaccines used worldwide have been developed using live attenuated platforms. The recent development of a reverse genetics system for RVs has delivered the possibility of engineering chimeric viruses expressing heterologous peptides from other virus species to generate polyvalent vaccines. We tested the feasibility of this using two approaches. Firstly, we inserted short SARS-CoV-2 spike peptides into the hypervariable region of the simian SA11 RV strain viral protein (VP) 4. Secondly, we fused the receptor binding domain (RBD) of the SARS-CoV-2 spike protein, or the shorter receptor binding motif (RBM) nested within the RBD, to the C-terminus of non-structural protein (NSP) 3 of the bovine RF strain RV, with or without an intervening T2A peptide. Mutating the hypervariable region of SA11 VP4 impeded viral replication, and for these mutants no cross-reactivity with spike antibodies was detected. To rescue NSP3 mutants, we established a plasmid-based reverse genetics system for the bovine RF strain. Except for the RBD mutant, all NSP3 mutants delivered endpoint titres and replication kinetics comparable to that of the WT virus. In ELISAs, cell lysates of an NSP3 mutant expressing the RBD peptide showed cross reactivity with a SARS-CoV-2 RBD antibody. 3D bovine gut enteroids were susceptible to infection by all NSP3 mutants but only RBM mutant showed cross reactivity with SARS-CoV-2 RBD antibody. The tolerability of large peptide insertions in the NSP3 segment highlights the potential for this approach in the development of vaccine vectors targeting multiple enteric pathogens simultaneously. IMPORTANCEWe explored the use of rotaviruses (RVs) to express heterologous peptides, using SARS-CoV-2 as an exemplar. Small SARS-CoV-2 peptide insertion (<34 amino acids) into the hypervariable region of the viral protein 4 (VP4) of RV SA11 strain resulted in reduced viral titre and replication, thus limiting its use as a potential vaccine expression platform. To test RF strain for its tolerance for peptide insertions, we constructed a reverse genetics system. NSP3 was C-terminally tagged with SARS-CoV-2 spike peptides of up to 193 amino acids. With a T2A-separated 193 amino acid tag on NSP3, there was little effect on the viral rescue efficiency, titre and replication. Tagged NSP3 elicited cross-reactivity with SARS-CoV-2 spike antibodies in ELISA. This is the first report describing epitope tagging of VP4, and of a reverse genetics system for the RF strain. We highlight the potential for development of RV vaccine vectors targeting multiple enteric pathogens simultaneously.