Ferret model to mimic the sequential exposure of humans to historical H3N2 influenza viruses

Development of broadly protective influenza B vaccines

Influenza B viruses pose a significant threat to global public health, leading to severe respiratory infections in humans and, in some cases, death. During the last 50 years, influenza B viruses of two antigenically distinct lineages (termed 'Victoria' and 'Yamagata') have circulated in humans, necessitating two different influenza B vaccine strains. In this study, we devised a novel vaccine strategy involving reciprocal amino acid substitutions at sites where Victoria- and Yamagata-lineage viruses differ, leading to the generation of 'hybrid' vaccine viruses with the potential to protect against both lineages. Based on antigenic characterization, we selected two candidates and assessed their protective efficacy in a ferret model. Notably, both recombinant HA proteins conferred enhanced protection against heterologous challenges compared to their respective wild-type antigens. These findings show the potential of our novel strategy to develop cross-lineage protective influenza B virus vaccines.

Intranasal administration of octavalent next-generation influenza vaccine elicits protective immune responses against seasonal and pre-pandemic viruses

Development of next-generation influenza virus vaccines is crucial to improve protection against circulating and emerging viruses. Current vaccine formulations have to be updated annually due to mutations in seasonal strains and do not offer protection against strains with pandemic potential. Computationally optimized broadly reactive antigen (COBRA) methodology has been utilized by our group to generate broadly reactive immunogens for individual influenza subtypes, which elicit protective immune responses against a broad range of strains over numerous seasons. Octavalent mixtures of COBRA hemagglutinin (HA) (H1, H2, H3, H5, H7, and influenza B virus) plus neuraminidase (NA) (N1 and N2) recombinant proteins mixed with c-di-AMP adjuvant were administered intranasally to naive or pre-immune ferrets in prime-boost fashion. Four weeks after final vaccination, collected sera were analyzed for breadth of antibody response, and the animals were challenged with seasonal or pre-pandemic strains. The octavalent COBRA vaccine elicited antibodies that recognized a broad panel of strains representing different subtypes, and these vaccinated animals were protected against influenza virus challenges. Overall, this study demonstrated that the mixture of eight COBRA HA/NA proteins mixed with an intranasal adjuvant is a promising candidate for a universal influenza vaccine.

IMPORTANCE

Influenza is a respiratory virus which infects around a billion people globally every year, with millions experiencing severe illness. Commercial vaccine efficacy varies year to year and can be low due to mismatch of circulating virus strains. Thus, the formulation of current vaccines has to be adapted accordingly every year. The development of a broadly reactive influenza vaccine would lessen the global economic and public health burden caused by the different types of influenza viruses. The significance of our research is producing a promising universal vaccine candidate which provides protection against a wider range of virus strains over a wider range of time.

Tonsil explants as a human in vitro model to study vaccine responses

Introduction

Vaccination is one of the most effective infection prevention strategies. Viruses with high mutation rates -such as influenza- escape vaccine-induced immunity and represent significant challenges to vaccine design. Influenza vaccine strain selection is based on circulating strains and immunogenicity testing in animal models with limited predictive outcomes for vaccine effectiveness in humans.

Methods

We developed a human in vitro vaccination model using human tonsil tissue explants cultured in 3D perfusion bioreactors to be utilized as a platform to test and improve vaccines.

Results

Tonsils cultured in bioreactors showed higher viability, metabolic activity, and more robust immune responses than those in static cultures. The in vitro vaccination system responded to various premanufactured vaccines, protein antigens, and antigen combinations. In particular, a multivalent in vitro immunization with three phylogenetically distant H3N2 influenza strains showed evidence for broader B cell activation and induced higher antibody cross-reactivity than combinations with more related strains. Moreover, we demonstrate the capacity of our in vitro model to generate de novo humoral immune responses to a model antigen.

Discussion

Perfusion-cultured tonsil tissue may be a valuable human in vitro model for immunology research with potential application in vaccine candidate selection.

Single immunization with an influenza hemagglutinin nanoparticle-based vaccine elicits durable protective immunity

Vaccination is the most effective strategy to combat influenza. Ideally, potent and persistent vaccine effects would be induced with a single vaccine dose. Here, we designed a virus-like particle (VLP)-based vaccine presenting multiple copies of the influenza hemagglutinin (HA) from A/Puerto Rico/8/1934 (PR8HA-VLP) and examined its immunogenicity and protective efficacy in ferrets. Serum-neutralizing antibodies were effectively induced against the homologous virus at 3-week post-vaccination with a single dose of PR8HA-VLP with or without adjuvants. When the single-immunized ferrets were challenged with the homologous virus, virus replication in the nasal mucosa was significantly reduced. Long-term monitoring of serum titers revealed that after adjuvanted vaccination with PR8HA-VLP, neutralizing antibodies were retained at similar levels 20- to 183-week post-vaccination, although a 4- to 8-fold titer decline was observed from 3- to 20-week post-vaccination. Boost immunization at 183 weeks after the first immunization elicited higher neutralizing antibody titers than those at 3 weeks after the initial immunization in most of the animals. These results confirm that nanoparticle-based vaccines are a promising approach to effectively elicit durable multiyear neutralizing antibody responses against influenza viruses.

Infection with Seasonal H1N1 Influenza Results in Comparable Disease Kinetics and Host Immune Responses in Ferrets and Golden Syrian Hamsters

Animal models of influenza are important in preclinical research for the study of influenza infection and the assessment of vaccines, drugs and therapeutics. Here, we show that Golden Syrian hamsters (Mesocricetus auratus) inoculated via the intranasal route with high dose of influenza H1N1 display comparable disease kinetics and immune responses to the 'gold standard' ferret (Mustela furo) model. We demonstrate that both the hamster and ferret models have measurable disease endpoints of weight loss, temperature change, viral shedding from the upper respiratory tract and increased lung pathology. We also characterised both the humoral and cellular immune responses to infection in both models. The comparability of these data supports the Golden Syrian hamster model being useful in preclinical evaluation studies to explore the efficacy of countermeasures against influenza.

Mapping the Antibody Repertoires in Ferrets with Repeated Influenza A/H3 Infections: Is Original Antigenic Sin Really "Sinful"?

The influenza-specific antibody repertoire is continuously reshaped by infection and vaccination. The host immune response to contemporary viruses can be redirected to preferentially boost antibodies specific for viruses encountered early in life, a phenomenon called original antigenic sin (OAS) that is suggested to be responsible for diminished vaccine effectiveness after repeated seasonal vaccination. Using a new computational tool called Neutralization Landscapes, we tracked the progression of hemagglutination inhibition antibodies within ferret antisera elicited by repeated influenza A/H3 infections and deciphered the influence of prior exposures on the de novo antibody response to evolved viruses. The results indicate that a broadly neutralizing antibody signature can nevertheless be induced by repeated exposures despite OAS induction. Our study offers a new way to visualize how immune history shapes individual antibodies within a repertoire, which may help to inform future universal influenza vaccine design.