Refining the approach to vaccines against influenza A viruses with pandemic potential

Non-neutralizing antibody responses following A(H1N1)pdm09 influenza vaccination with or without AS03 adjuvant system

Background

Non‐neutralizing antibodies inducing complement‐dependent lysis (CDL) and antibody‐dependent cell‐mediated cytotoxicity (ADCC) activity may contribute to protection against influenza infection. We investigated CDL and ADCC responses in healthy adults randomized to receive either non‐adjuvanted or AS03‐adjuvanted monovalent A(H1N1)pdm09 vaccine (containing 15 µg/3.75 μg of hemagglutinin, respectively) on a 2‐dose schedule 21 days apart.

Methods

We conducted an exploratory analysis of a subset of 106 subjects having no prior history of A(H1N1)pdm09 infection or seasonal influenza vaccination enrolled in a previously reported study (NCT00985673). Antibody responses against the homologous A/California/7/2009 (H1N1) vaccine strain and a related A/Brisbane/59/2007 (H1N1) seasonal influenza strain were analyzed up to Day 42.

Results

Baseline seropositivity determined with hemagglutination inhibition (HI), CDL and ADCC antibody titers against viral strains was high; A/California/7/2009 (HI [40.4‐48.1%]; CDL [34.6‐36.0%]; ADCC [92.1‐92.3%]); A/Brisbane/59/2007 (HI [73.1‐88.9%]; CDL [38.0‐42.0%]; ADCC [86.8‐97.0%]). CDL seropositivity increased following vaccination with both adjuvanted and non‐adjuvanted formulations (A/California/7/2009 [95.9‐100%]; A/Brisbane/59/2007 [75.5‐79.6%]). At Day 21, increases in CDL and ADCC antibody geometric mean titers against both strains were observed for both formulations. After 2 doses of AS03‐adjuvanted vaccine, vaccine responses of 95.8% (≥9‐fold increase from baseline in CDL titers) and 34.3% (≥16‐fold increase from baseline in ADCC titers) were seen against A/California/7/2009; and 22.4% and 42.9%, respectively, against A/Brisbane/59/2007. Vaccine responses after 2 doses of the non‐adjuvanted vaccine were broadly similar.

Conclusions

Broadly comparable non‐neutralizing immune responses were observed following vaccination with non‐adjuvanted and AS03‐adjuvanted A(H1N1)pdm09 formulations; including activity against a related vaccine strain.

Could Environment Affect the Mutation of H1N1 Influenza Virus?

H1N1 subtype influenza A viruses are the most common type of influenza A virus to infect humans. The two major outbreaks of the virus in 1918 and 2009 had a great impact both on human health and social development. Though data on their complete genome sequences have recently been obtained, the evolution and mutation of A/H1N1 viruses remain unknown to this day. Among many drivers, the impact of environmental factors on mutation is a novel hypothesis worth studying. Here, a geographically disaggregated method was used to explore the relationship between environmental factors and mutation of A/H1N1 viruses from 2000-2019. All of the 11,721 geo-located cases were examined and the data was analysed of six environmental elements according to the time and location (latitude and longitude) of those cases. The main mutation value was obtained by comparing the sequence of the influenza virus strain with the earliest reported sequence. It was found that environmental factors systematically affect the mutation of A/H1N1 viruses. Minimum temperature displayed a nonlinear, rising association with mutation, with a maximum ~15 °C. The effects of precipitation and social development index (nighttime light) were more complex, while population density was linearly and positively correlated with mutation of A/H1N1 viruses. Our results provide novel insight into understanding the complex relationships between mutation of A/H1N1 viruses and environmental factors.

Influenza in temperate and tropical Asia: a review of epidemiology and vaccinology

The impact of seasonal influenza has been under-appreciated in Asia and surveillance data lags in most other regions. The variety of influenza circulation patterns in Asia – largely due to the range of climates – has also only recently been recognized and its effect on the burden of disease is not fully understood. Recent reports that clinical protection wanes in the weeks after influenza vaccination emphasize the importance of optimally timing vaccination to local epidemiology. It also raises questions as to whether influenza vaccines should be administered more frequently than annually and what may be the benefits in Asia of access to new vaccines with enhanced immunogenicity and effectiveness. This review will summarize influenza surveillance data from Asian countries over 2011–2018, and consider the implications for vaccination strategies in different parts of Asia.

Synthetic biology and healthcare

Through the application of the engineering paradigm of ‘design–build–test–learn’ allied to recent advances in DNA sequencing, bioinformatics and, critically, the falling cost of DNA synthesis, Synthetic Biology promises to make existing therapies more accessible and be at the centre of the development of new types of advanced therapies. As existing pharmaceutical companies integrate Synthetic Biology tools into their normal ways of working, existing products are being produced by cheaper and more sustainable methods. Vaccine design and production is becoming driven by the molecular design allied to rapidly scalable production methods to combat the threat of pandemics and the ability of pathogens to escape the immune system by mutation. Advanced therapies, such as chimeric antigen receptor T cell therapy, are able to capitalise on the tools of Synthetic Biology to design new proteins and molecular ‘kill switches’ as well as design scalable and effective vectors for cellular transduction. This review highlights how Synthetic Biology is having an impact across the various therapeutic modalities from existing products to new therapies.

The Critical Interspecies Transmission Barrier at the Animal⁻Human Interface

Influenza A viruses (IAVs) infect humans and a wide range of animal species in nature, and waterfowl and shorebirds are their reservoir hosts. Of the 18 haemagglutinin (HA) and 11 neuraminidase (NA) subtypes of IAV, 16 HA and 9 NA subtypes infect aquatic birds. However, among the diverse pool of IAVs in nature, only a limited number of animal IAVs cross the species barrier to infect humans and a small subset of those have spread efficiently from person to person to cause an influenza pandemic. The ability to infect a different species, replicate in the new host and transmit are three distinct steps in this process. Viral and host factors that are critical determinants of the ability of an avian IAV to infect and spread in humans are discussed.

Sowing the Seeds of a Pandemic? Mammalian Pathogenicity and Transmissibility of H1 Variant Influenza Viruses from the Swine Reservoir

Emergence of genetically and antigenically diverse strains of influenza to which the human population has no or limited immunity necessitates continuous risk assessments to determine the likelihood of these viruses acquiring adaptations that facilitate sustained human-to-human transmission. As the North American swine H1 virus population has diversified over the last century by means of both antigenic drift and shift, in vivo assessments to study multifactorial traits like mammalian pathogenicity and transmissibility of these emerging influenza viruses are critical. In this review, we examine genetic, molecular, and pathogenicity and transmissibility data from a panel of contemporary North American H1 subtype swine-origin viruses isolated from humans, as compared to H1N1 seasonal and pandemic viruses, including the reconstructed 1918 virus. We present side-by-side analyses of experiments performed in the mouse and ferret models using consistent experimental protocols to facilitate enhanced interpretation of in vivo data. Contextualizing these analyses in a broader context permits a greater appreciation of the role that in vivo risk assessment experiments play in pandemic preparedness. Collectively, we find that despite strain-specific heterogeneity among swine-origin H1 viruses, contemporary swine viruses isolated from humans possess many attributes shared by prior pandemic strains, warranting heightened surveillance and evaluation of these zoonotic viruses.

Antigenically Diverse Swine Origin H1N1 Variant Influenza Viruses Exhibit Differential Ferret Pathogenesis and Transmission Phenotypes

Influenza A(H1) viruses circulating in swine represent an emerging virus threat, as zoonotic infections occur sporadically following exposure to swine. A fatal infection caused by an H1N1 variant (H1N1v) virus was detected in a patient with reported exposure to swine and who presented with pneumonia, respiratory failure, and cardiac arrest. To understand the genetic and phenotypic characteristics of the virus, genome sequence analysis, antigenic characterization, and ferret pathogenesis and transmissibility experiments were performed. Antigenic analysis of the virus isolated from the fatal case, A/Ohio/09/2015, demonstrated significant antigenic drift away from the classical swine H1N1 variant viruses and H1N1 pandemic 2009 viruses. A substitution in the H1 hemagglutinin (G155E) was identified that likely impacted antigenicity, and reverse genetics was employed to understand the molecular mechanism of antibody escape. Reversion of the substitution to 155G, in a reverse genetics A/Ohio/09/2015 virus, showed that this residue was central to the loss of hemagglutination inhibition by ferret antisera raised against a prototypical H1N1 pandemic 2009 virus (A/California/07/2009), as well as gamma lineage classical swine H1N1 viruses, demonstrating the importance of this residue for antibody recognition of this H1 lineage. When analyzed in the ferret model, A/Ohio/09/2015 and another H1N1v virus, A/Iowa/39/2015, as well as A/California/07/2009, replicated efficiently in the respiratory tract of ferrets. The two H1N1v viruses transmitted efficiently among cohoused ferrets, but respiratory droplet transmission studies showed that A/California/07/2009 transmitted through the air more efficiently. Preexisting immunity to A/California/07/2009 did not fully protect ferrets from challenge with A/Ohio/09/2015.IMPORTANCE Human infections with classical swine influenza A(H1N1) viruses that circulate in pigs continue to occur in the United States following exposure to swine. To understand the genetic and virologic characteristics of a virus (A/Ohio/09/2015) associated with a fatal infection and a virus associated with a nonfatal infection (A/Iowa/39/2015), we performed genome sequence analysis, antigenic testing, and pathogenicity and transmission studies in a ferret model. Reverse genetics was employed to identify a single antigenic site substitution (HA G155E) responsible for antigenic variation of A/Ohio/09/2015 compared to related classical swine influenza A(H1N1) viruses. Ferrets with preexisting immunity to the pandemic A(H1N1) virus were challenged with A/Ohio/09/2015, demonstrating decreased protection. These data illustrate the potential for currently circulating swine influenza viruses to infect and cause illness in humans with preexisting immunity to H1N1 pandemic 2009 viruses and a need for ongoing risk assessment and development of candidate vaccine viruses for improved pandemic preparedness.

Development of Clade-Specific and Broadly Reactive Live Attenuated Influenza Virus Vaccines against Rapidly Evolving H5 Subtype Viruses

We have developed pandemic live attenuated influenza vaccines (pLAIVs) against clade 1 H5N1 viruses on an Ann Arbor cold-adapted (ca) backbone that induced long-term immune memory. In 2015, many human infections caused by a new clade (clade 2.2.1.1) of goose/Guangdong (gs/GD) lineage H5N1 viruses were reported in Egypt, which prompted updating of the H5N1 pLAIV. We explored two strategies to generate suitable pLAIVs. The first approach was to modify the hemagglutinin gene of a highly pathogenic wild-type (wt) clade 2.2.1.1 virus, A/Egypt/N03434/2009 (Egy/09) (H5N1), with its unmodified neuraminidase (NA) gene; this virus was designated Egy/09 ca The second approach was to select a low-pathogenicity avian influenza H5 virus that elicited antibodies that cross-reacted with a broad range of H5 viruses, including the Egypt H5N1 viruses, and contained a novel NA subtype for humans. We selected the low-pathogenicity A/duck/Hokkaido/69/2000 (H5N3) (dk/Hok/00) virus for this purpose. Both candidate vaccines were attenuated and immunogenic in ferrets, inducing antibodies that neutralized homologous and heterologous H5 viruses with different degrees of cross-reactivity; Egy/09 ca vaccine antisera were more specific for the gs/GD lineage viruses but did not neutralize recent North American isolates (clade 2.3.4.4), whereas antisera from dk/Hok/69 ca-vaccinated ferrets cross-reacted with clade 2.3.4.4 and 2.2.1 viruses but not clade 1 or 2.1 viruses. When vaccinated ferrets were challenged with homologous and heterologous H5 viruses, challenge virus replication was reduced in the respiratory tract. Thus, the two H5 pLAIV candidates are suitable for clinical development to protect humans from infection with different clades of H5 viruses.IMPORTANCE In response to the continuing evolution of H5N1 avian influenza viruses and human infections, new candidate H5 live attenuated vaccines were developed by using two different approaches: one targeted a specific circulating strain in Egypt, and the other was based on a virus that elicits broadly cross-reactive antibodies against a wide range of H5 viruses. Both candidate vaccines were immunogenic and exhibited protective efficacy in ferrets. Our study permits a comparison of the two approaches, and the data support the further development of both vaccine viruses to optimally prepare for the further spread of clade 2.2.1 or 2.3.4.4 viruses.

Evaluating influenza vaccines: progress and perspectives

Severe influenza infections are responsible for 3–5 million cases worldwide and 250,000–500,000 deaths per year. Although vaccination is the primary and most effective means of inducing protection against influenza viruses, it also presents limitations. This review outlines the promising steps that have been taken toward the development of a broadly protective influenza virus vaccine through the use of new technologies. The future challenge is to develop a broadly protective vaccine that is able to induce long-term protection against antigenically variant influenza viruses, regardless of antigenic shift and drift, and thus to protect against seasonal and pandemic influenza viruses.