Assessment of the antigenic evolution of a clade 6B.1 human H1N1pdm influenza virus revealed differences between ferret and human convalescent sera.

BACKGROUND: Influenza viruses continually acquire mutations in the antigenic epitopes of their major viral antigen, the surface glycoprotein haemagglutinin (HA), allowing evasion from immunity in humans induced upon prior influenza virus infections or vaccinations. Consequently, the influenza strains used for vaccine production must be updated frequently. METHODS: To better understand the antigenic evolution of influenza viruses, we introduced random mutations into the HA head region (where the immunodominant epitopes are located) of a pandemic H1N1 (H1N1pdm) virus from 2015 and incubated it with various human sera collected in 2015-2016. Mutants not neutralized by the human sera were sequenced and further characterized for their haemagglutination inhibition (HI) titers with human sera and with ferret sera raised to H1N1pdm viruses from 2009 to 2015. FINDINGS: The largest antigenic changes were conferred by mutations at HA amino acid position 187; interestingly, these antigenic changes were recognized by human, but not by ferret serum. H1N1pdm viruses with amino acid changes at position 187 were very rare until the end of 2018, but have become more frequent since; in fact, the D187A amino acid change is one of the defining changes of clade 6B.1A.5a.1 viruses, which emerged in 2019. INTERPRETATION: Our findings indicate that amino acid substitutions in H1N1pdm epitopes may be recognized by human sera, but not by homologous ferret sera. FUNDING: This project was supported by funding from the NIAID-funded Center for Research on Influenza Pathogenesis (CRIP, HHSN272201400008C).

Influence of Physicochemical Properties of Lipopeptide Adjuvants on the Immune Response: A Rationale for Engineering a Potent Vaccine.

Adjuvant development and understanding the physicochemical properties of particles and interpreting the subsequent immunological responses is a challenge faced by many researchers in the vaccine field. We synthesized and investigated the physicochemical properties and immunogenicity of a library of multiple epitope self-adjuvant lipopeptides in a novel asymmetric arrangement. Vaccine candidates were synthesized using a combination of solid-phase peptide synthesis and copper-mediated click chemistry. In vivo studies showed that vaccine constructs containing a single OVA CD8+ T-cell epitope and two N-terminally located C16 lipid moieties were more effective at generating robust cellular immune responses compared to the same molecule containing multiple copies of the OVA CD8+ T-cell epitope with or without the C16 moieties. Furthermore, attachment of the two C16 lipids to the N-terminus provoked formation of long ß-sheet fibrils and was shown to induce a higher CD8+ donor T-cell frequency and IFN-γ secretion, compared to vaccine constructs with an internal lipid placement. A regression analysis indicated that particle secondary structure had a significant impact on CD8+ donor T-cell frequency and cytolytic activity. In addition, IFN-γ production was influenced significantly by particle shape. The findings of this research will impact the future design of a vaccine intended to elicit cellular immune responses.