Sequential Immunizations with heterosubtypic virus-like particles elicit cross protection against divergent influenza A viruses in mice

Vaccine design via antigen reorientation

A major challenge in creating universal influenza vaccines is to focus immune responses away from the immunodominant, variable head region of hemagglutinin (HA-head) and toward the evolutionarily conserved stem region (HA-stem). Here we introduce an approach to control antigen orientation via site-specific insertion of aspartate residues that facilitates antigen binding to alum. We demonstrate the generalizability of this approach with antigens from Ebola, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza viruses and observe enhanced neutralizing antibody responses in all cases. We then reorient an H2 HA in an 'upside-down' configuration to increase the exposure and immunogenicity of HA-stem. The reoriented H2 HA (reoH2HA) on alum induced stem-directed antibodies that cross-react with both group 1 and group 2 influenza A subtypes. Electron microscopy polyclonal epitope mapping (EMPEM) revealed that reoH2HA (group 1) elicits cross-reactive antibodies targeting group 2 HA-stems. Our results highlight antigen reorientation as a generalizable approach for designing epitope-focused vaccines.

Bringing immunofocusing into focus

Immunofocusing is a strategy to create immunogens that redirect humoral immune responses towards a targeted epitope and away from non-desirable epitopes. Immunofocusing methods often aim to develop "universal" vaccines that provide broad protection against highly variant viruses such as influenza virus, human immunodeficiency virus (HIV-1), and most recently, severe acute respiratory syndrome coronavirus (SARS-CoV-2). We use existing examples to illustrate five main immunofocusing strategies-cross-strain boosting, mosaic display, protein dissection, epitope scaffolding, and epitope masking. We also discuss obstacles for immunofocusing like immune imprinting. A thorough understanding, advancement, and application of the methods we outline here will enable the design of high-resolution vaccines that protect against future viral outbreaks.

Influenza vaccine: a review on current scenario and future prospects

Vaccination is a crucial tool in preventing influenza, but it requires annual updates in vaccine composition due to the ever-changing nature of the flu virus. While healthcare and economic burdens have reduced, the virus remains a challenge. Research conducted over the past decade has revealed pathways for improvement through both basic and clinical studies. Viral surveillance plays a vital role in the better selection of candidate viruses for vaccines and the early detection of drug-resistant strains.This page offers a description of future vaccine developments and an overview of current vaccine options. In the coming years, we anticipate significant changes in vaccine production, moving away from traditional egg-based methods towards innovative technologies such as DNA and RNA vaccines. These newer approaches offer significant advantages over traditional egg-based and cell culture-based influenza vaccine manufacturing.

Designing epitope-focused vaccines via antigen reorientation

A major challenge in vaccine development, especially against rapidly evolving viruses, is the ability to focus the immune response toward evolutionarily conserved antigenic regions to confer broad protection. For example, while many broadly neutralizing antibodies against influenza have been found to target the highly conserved stem region of hemagglutinin (HA-stem), the immune response to seasonal influenza vaccines is predominantly directed to the immunodominant but variable head region (HA-head), leading to narrow-spectrum efficacy. Here, we first introduce an approach to controlling antigen orientation based on the site-specific insertion of short stretches of aspartate residues (oligoD) that facilitates antigen-binding to alum adjuvants. We demonstrate the generalizability of this approach to antigens from the Ebola virus, SARS-CoV-2, and influenza and observe enhanced antibody responses following immunization in all cases. Next, we use this approach to reorient HA in an "upside down" configuration, which we envision increases HA-stem exposure, therefore also improving its immunogenicity compared to HA-head. When applied to HA of H2N2 A/Japan/305/1957, the reoriented H2 HA (reoH2HA) on alum induced a stem-directed antibody response that cross-reacted with both group 1 and 2 influenza A HAs. Our results demonstrate the possibility and benefits of antigen reorientation via oligoD insertion, which represents a generalizable immunofocusing approach readily applicable for designing epitope-focused vaccine candidates.

Designing epitope-focused vaccines via antigen reorientation

A major challenge in vaccine development, especially against rapidly evolving viruses, is the ability to focus the immune response toward evolutionarily conserved antigenic regions to confer broad protection. For example, while many broadly neutralizing antibodies against influenza have been found to target the highly conserved stem region of hemagglutinin (HA-stem), the immune response to seasonal influenza vaccines is predominantly directed to the immunodominant but variable head region (HA-head), leading to narrow-spectrum efficacy. Here, we first introduce an approach to controlling antigen orientation based on the site-specific insertion of short stretches of aspartate residues (oligoD) that facilitates antigen-binding to alum adjuvants. We demonstrate the generalizability of this approach to antigens from the Ebola virus, SARS-CoV-2, and influenza and observe enhanced antibody responses following immunization in all cases. Next, we use this approach to reorient HA in an "upside down" configuration, which we envision increases HA-stem exposure, therefore also improving its immunogenicity compared to HA-head. When applied to HA of H2N2 A/Japan/305/1957, the reoriented H2 HA (reoH2HA) on alum induced a stem-directed antibody response that cross-reacted with both group 1 and 2 influenza A HAs. Our results demonstrate the possibility and benefits of antigen reorientation via oligoD insertion, which represents a generalizable immunofocusing approach readily applicable for designing epitope-focused vaccine candidates.

GRAPHICAL ABSTRACT

Seasonal influenza vaccines induce a biased antibody response against the variable head of hemagglutinin, whereas conserved epitopes on the stem are a target for universal vaccines. Here we show that reorienting HA in an "upside-down" configuration sterically occludes the head and redirects the antibody response to the more exposed stem, thereby inducing broad cross-reactivity against hemagglutinins from diverse influenza strains.

Progress towards the Development of a Universal Influenza Vaccine

Influenza viruses are responsible for millions of cases globally and significantly threaten public health. Since pandemic and zoonotic influenza viruses have emerged in the last 20 years and some of the viruses have resulted in high mortality in humans, a universal influenza vaccine is needed to provide comprehensive protection against a wide range of influenza viruses. Current seasonal influenza vaccines provide strain-specific protection and are less effective against mismatched strains. The rapid antigenic drift and shift in influenza viruses resulted in time-consuming surveillance and uncertainty in the vaccine protection efficacy. Most recent universal influenza vaccine studies target the conserved antigen domains of the viral surface glycoproteins and internal proteins to provide broader protection. Following the development of advanced vaccine technologies, several innovative strategies and vaccine platforms are being explored to generate robust cross-protective immunity. This review provides the latest progress in the development of universal influenza vaccines.

An Overview of Influenza Viruses and Vaccines

Influenza remains one of the major public health concerns because it causes annual epidemics and can potentially instigate a global pandemic. Numerous countermeasures, including vaccines and antiviral treatments, are in use against seasonal influenza infection; however, their effectiveness has always been discussed due to the ongoing resistance to antivirals and relatively low and unpredictable efficiency of influenza vaccines compared to other vaccines. The growing interest in vaccines as a promising approach to prevent and control influenza may provide alternative vaccine development options with potentially increased efficiency. In addition to currently available inactivated, live-attenuated, and recombinant influenza vaccines on the market, novel platforms such as virus-like particles (VLPs) and nanoparticles, and new vaccine formulations are presently being explored. These platforms provide the opportunity to design influenza vaccines with improved properties to maximize quality, efficacy, and safety. The influenza vaccine manufacturing process is also moving forward with advancements relating to egg- and cell-based production, purification processes, and studies into the physicochemical attributes and vaccine degradation pathways. These will contribute to the design of more stable, optimized vaccine formulations guided by contemporary analytical testing methods and via the implementation of the latest advances in the field.

B Cell Responses against Influenza Viruses: Short-Lived Humoral Immunity against a Life-Long Threat

Antibodies are critical for providing protection against influenza virus infections. However, protective humoral immunity against influenza viruses is limited by the antigenic drift and shift of the major surface glycoproteins, hemagglutinin and neuraminidase. Importantly, people are exposed to influenza viruses throughout their life and tend to reuse memory B cells from prior exposure to generate antibodies against new variants. Despite this, people tend to recall memory B cells against constantly evolving variable epitopes or non-protective antigens, as opposed to recalling them against broadly neutralizing epitopes of hemagglutinin. In this review, we discuss the factors that impact the generation and recall of memory B cells against distinct viral antigens, as well as the immunological limitations preventing broadly neutralizing antibody responses. Lastly, we discuss how next-generation vaccine platforms can potentially overcome these obstacles to generate robust and long-lived protection against influenza A viruses.

Nanoparticles in influenza subunit vaccine development: Immunogenicity enhancement

The threat of novel influenza infections has sparked research efforts to develop subunit vaccines that can induce a more broadly protective immunity by targeting selected regions of the virus. In general, subunit vaccines are safer but may be less immunogenic than whole cell inactivated or live attenuated vaccines. Hence, novel adjuvants that boost immunogenicity are increasingly needed as we move toward the era of modern vaccines. In addition, targeting, delivery, and display of the selected antigens on the surface of professional antigen-presenting cells are also important in vaccine design and development. The use of nanosized particles can be one of the strategies to enhance immunogenicity as they can be efficiently recognized by antigen-presenting cells. They can act as both immunopotentiators and delivery system for the selected antigens. This review will discuss on the applications, advantages, limitations, and types of nanoparticles (NPs) used in the preparation of influenza subunit vaccine candidates to enhance humoral and cellular immune responses.

Vaccine Efficacy Induced by 2009 Pandemic H1N1 Virus-Like Particles Differs from that Induced by Split Influenza Virus

Influenza virus-like particles (VLPs) vaccines are highly immunogenic, showing strong protective efficacy against homologous virus infection compared to split vaccine. However, a comparative efficacy study against heterosubtypic virus infection between VLPs and split vaccine has yet to been reported. In this study, we generated VLPs vaccine containing hemagglutinin (HA) and matrix protein (M1) of the 2009 pandemic H1N1, and investigated the protective efficacies induced by VLPs vaccine and commercial monovalent H1N1 pandemic split vaccine from Sanofi-Pasteur. Mice were intramuscularly immunized with either VLPs vaccine or split vaccine and subsequently challenge-infected with homologous virus (A/California/04/2009, H1N1) or heterosubtypic virus (A/Philippines/82, H3N2) after 4.5 months. VLPs vaccination demonstrated a higher level of protective efficacy against homologous viruses compared to split vaccine, as lessened lung viral loads and minuscule levels of proinflammatory lung cytokines IFN-gamma and IL-6 were observed. Protective efficacies were close to non-existent in VLP-immunized mice challenged with heterosubtypic viruses (H3N2). In contrast, split vaccine showed lower vaccine efficacy against homologous virus than VLP vaccine, but conferred better protection against heterosubtypic viruses through lung viral loads reduction and heightened survival rate. These results indicate that influenza VLPs provide better protective efficacy against homologous virus challenge infection, whereas split vaccine shows better protective efficacy against heterosubtypic virus challenge. Findings from the current study contribute to the rational design of vaccines conferring a broad range of protection.

Development of Universal Influenza Vaccines Targeting Conserved Viral Proteins

Vaccination is still the most efficient way to prevent an infection with influenza viruses. Nevertheless, existing commercial vaccines face serious limitations such as availability during epidemic outbreaks and their efficacy. Existing seasonal influenza vaccines mostly induce antibody responses to the surface proteins of influenza viruses, which frequently change due to antigenic shift and or drift, thus allowing influenza viruses to avoid neutralizing antibodies. Hence, influenza vaccines need a yearly formulation to protect against new seasonal viruses. A broadly protective or universal influenza vaccine must induce effective humoral as well as cellular immunity against conserved influenza antigens, offer good protection against influenza pandemics, be safe, and have a fast production platform. Nanotechnology has great potential to improve vaccine delivery, immunogenicity, and host immune responses. As new strains of human epidemic influenza virus strains could originate from poultry and swine viruses, development of a new universal influenza vaccine will require the immune responses to be directed against viruses from different hosts. This review discusses how the new vaccine platforms and nanoparticles can be beneficial in the development of a broadly protective, universal influenza vaccine.

Subunit vaccines based on recombinant yeast protect against influenza A virus in a one-shot vaccination scheme

Here we report on new subunit vaccines based on recombinant yeast of the type Kluyveromyces lactis (K. lactis), which protect mice from a lethal influenza A virus infection. Applying a genetic system that enables the rapid generation of transgenic yeast, we have developed K. lactis strains that express the influenza A virus hemagglutinin, HA, either individually or in combination with the viral M1 matrix protein. Subcutaneous application of the inactivated, but otherwise non-processed yeast material shows a complete protection of BALB/c mice in prime/boost and even one-shot/single dose vaccination schemes against a subsequent, lethal challenge with the cognate influenza virus. The yeast vaccines induce titers of neutralizing antibodies that are readily comparable to those induced by an inactivated virus vaccine. These data suggest that HA and M1 are produced with a high antigenicity in the yeast cells. Based on these findings, multivalent, DIVA-capable, yeast-based subunit vaccines may be developed as promising alternatives to conventional virus-based anti-flu vaccines for veterinary applications.

Development of broadly neutralizing antibodies in HIV-1 infected elite neutralizers

Broadly neutralizing antibodies (bNAbs), able to prevent viral entry by diverse global viruses, are a major focus of HIV vaccine design, with data from animal studies confirming their ability to prevent HIV infection. However, traditional vaccine approaches have failed to elicit these types of antibodies. During chronic HIV infection, a subset of individuals develops bNAbs, some of which are extremely broad and potent. This review describes the immunological and virological factors leading to the development of bNAbs in such "elite neutralizers". The features, targets and developmental pathways of bNAbs from their precursors have been defined through extraordinarily detailed within-donor studies. These have enabled the identification of epitope-specific commonalities in bNAb precursors, their intermediates and Env escape patterns, providing a template for vaccine discovery. The unusual features of bNAbs, such as high levels of somatic hypermutation, and precursors with unusually short or long antigen-binding loops, present significant challenges in vaccine design. However, the use of new technologies has led to the isolation of more than 200 bNAbs, including some with genetic profiles more representative of the normal immunoglobulin repertoire, suggesting alternate and shorter pathways to breadth. The insights from these studies have been harnessed for the development of optimized immunogens, novel vaccine regimens and improved delivery schedules, which are providing encouraging data that an HIV vaccine may soon be a realistic possibility.