PB2 and PA genes control the expression of the temperature-sensitive phenotype of cold-adapted B/USSR/60/69 influenza master donor virus

Development of Cross-Reactive Live Attenuated Influenza Vaccine Candidates against Both Lineages of Influenza B Virus

BACKGROUND

Influenza viruses continue to cause a significant social and economic burden globally. Vaccination is recognized as the most effective measure to control influenza. Live attenuated influenza vaccines (LAIVs) are an effective means of preventing influenza, especially among children. A reverse genetics (RG) system is required to rapidly update the antigenic composition of vaccines, as well as to design LAIVs with a broader spectrum of protection. Such a system has been developed for the Russian LAIVs only for type A strains, but not for influenza B viruses (IBV).

METHODS

All genes of the B/USSR/60/69 master donor virus (B60) were cloned into RG plasmids, and the engineered B60, as well as a panel of IBV LAIV reassortants were rescued from plasmid DNAs encoding all viral genes. The engineered viruses were evaluated in vitro and in a mouse model.

RESULTS

The B60 RG system was successfully developed, which made it possible to rescue LAIV reassortants with the desired antigenic composition, including hybrid strains with hemagglutinin and neuraminidase genes belonging to the viruses from different IBV lineages. The LAIV candidate carrying the HA of the B/Victoria-lineage virus and NA from the B/Yamagata-lineage virus demonstrated optimal characteristics in terms of safety, immunogenicity and cross-protection, prompting its further assessment as a broadly protective component of trivalent LAIV.

CONCLUSIONS

The new RG system for B60 MDV allowed the rapid generation of type B LAIV reassortants with desired genome compositions. The generation of hybrid LAIV reassortants with HA and NA genes belonging to the opposite IBV lineages is a promising approach for the development of IBV vaccines with broad cross-protection.

Clade 2.3.4.4 H5 chimeric cold-adapted attenuated influenza vaccines induced cross-reactive protection in mice and ferrets

IMPORTANCE

Clade 2.3.4.4 H5Nx avian influenza viruses (AIVs) have circulated globally and caused substantial economic loss. Increasing numbers of humans have been infected with Clade 2.3.4.4 H5N6 AIVs in recent years. Only a few human influenza vaccines have been licensed to date. However, the licensed live attenuated influenza virus vaccine exhibited the potential of being recombinant with the wild-type influenza A virus (IAV). Therefore, we developed a chimeric cold-adapted attenuated influenza vaccine based on the Clade 2.3.4.4 H5 AIVs. These H5 vaccines demonstrate the advantage of being non-recombinant with circulated IAVs in the future influenza vaccine study. The findings of our current study reveal that these H5 vaccines can induce cross-reactive protective efficacy in mice and ferrets. Our H5 vaccines may provide a novel option for developing human-infected Clade 2.3.4.4 H5 AIV vaccines.

DEVELOPMENT OF REASSORTANT INFLUENZA VACCINES: CLASSICAL REASSORTMENT OR REVERSE GENETICS?

An important feature of influenza vaccines, which distinguishes them from other immunobiological preparations, is that they have no fixed composition. Due to the constant influenza virus antigenic variability, production facilities require timely supply with relevant vaccine strains undoable due to the lack of proper method for the convenient, rapid and uninterrupted development of vaccine strains. Among the licensed influenza vaccines, classical inactivated and live influenza vaccines hold a special place. They are based on reassortant vaccine strains obtained by crossing currently circulating influenza virus with the so-called donor strain (cold-adapted attenuation donor for live influenza vaccines or high yield donor for inactivated vaccines). Vaccine strains for licensed live attenuated influenza vaccines are reassortants with the so-called 6:2 genome formula two genes encoding hemagglutinin and neuraminidase (HA and NA) belong to the current epidemic virus, and six genes encoding internal proteins (PB2, PB1, PA, NP, M and NS) to cold-adapted master donor virus. There is a very limited number of donors of attenuation. In Russia, there are cold-adapted viruses A/Leningrad/134/17/57 (H2N2) and B/USSR/60/69; in the USA (MedImmune) there are viruses A/Ann Arbor/6/60ca (H2N2) and B/Ann Arbor/1/66ca. MedImmune produces vaccine strains using reverse genetics technique. For other countries, this approach for obtaining vaccines is limited due to the need to purchase a license from the patent holders. In Russia, genetic manipulations with strains for the seasonal live influenza vaccine are not yet allowed; reassortants for the Russian live influenza vaccine are created only by classical reassortment in embryonated chicken eggs. Vaccine candidates for the inactivated influenza vaccine are prepared by the classical reassortment method, the requirements for them are more flexible and allow to use diverse genes combinations from wild type virus and master donor virus. High-yielding viruses such as A/PR/8/34 (H1N1), A/Texas/1/77 (H3N2), B/Lee/40 and some others are used as donors of internal genes. Unfortunately, the classical reassortment method does not always allow to promptly obtain a reassortant virus with a 6:2 genome formula. This is hindered by a number of reasons, ranging from the unique properties of a certain epidemic virus ending up with the constellation of genes. The reverse genetics method based on plasmids is an alternative approach to create reassortant vaccine strains allowing to reliably and quickly obtain reassortant viruses of a set 6:2 genome formula. However, this method also has certain weaknesses. This review discusses the advantages and disadvantages of development of conventional influenza vaccine candidates by reverse genetics and classical reassortment in developing chick embryos.

Current Opinion in LAIV: A Matter of Parent Virus Choice

Influenza is still a frequent seasonal infection of the upper respiratory tract, which may have deadly consequences, especially for the elderly. This is in spite of the availability of vaccines suggested for persons above 65 years of age. Two types of conventional influenza vaccines are currently licensed for use-live attenuated and inactivated vaccines. Depending on local regulatory requirements, live attenuated vaccines are produced by the reverse genetics technique or by classical reassortment in embryonated chicken eggs. Sometimes, the efficiency of classical reassortment is complicated by certain properties of the wild-type parent virus. Cases of low efficacy of vaccines have been noted, which, among other reasons, may be associated with suboptimal properties of the wild-type parent virus that are not considered when recommendations for influenza vaccine composition are made. Unfortunately, knowledge surrounding the roles of properties of the circulating influenza virus and its impact on the efficacy of the reassortment process, vaccination efficiency, the infectivity of the vaccine candidates, etc., is now scattered in different publications. This review summarizes the main features of the influenza virus that may dramatically affect different aspects of the preparation of egg-derived live attenuated vaccine candidates and their effectiveness. The author expresses her personal view, which may not coincide with the opinion of other experts in the field of influenza vaccines.

Recent Progress in Recombinant Influenza Vaccine Development Toward Heterosubtypic Immune Response

Flu, a viral infection caused by the influenza virus, is still a global public health concern with potential to cause seasonal epidemics and pandemics. Vaccination is considered the most effective protective strategy against the infection. However, given the high plasticity of the virus and the suboptimal immunogenicity of existing influenza vaccines, scientists are moving toward the development of universal vaccines. An important property of universal vaccines is their ability to induce heterosubtypic immunity, i.e., a wide immune response coverage toward different influenza subtypes. With the increasing number of studies and mounting evidence on the safety and efficacy of recombinant influenza vaccines (RIVs), they have been proposed as promising platforms for the development of universal vaccines. This review highlights the current progress and advances in the development of RIVs in the context of heterosubtypic immunity induction toward universal vaccine production. In particular, this review discussed existing knowledge on influenza and vaccine development, current hemagglutinin-based RIVs in the market and in the pipeline, other potential vaccine targets for RIVs (neuraminidase, matrix 1 and 2, nucleoprotein, polymerase acidic, and basic 1 and 2 antigens), and deantigenization process. This review also provided discussion points and future perspectives in looking at RIVs as potential universal vaccine candidates for influenza.

Understanding the Variability of Certain Biological Properties of H1N1pdm09 Influenza Viruses

The influenza virus continually evolves because of the high mutation rate, resulting in dramatic changes in its pathogenicity and other biological properties. This study aimed to evaluate the evolution of certain essential properties, understand the connections between them, and find the molecular basis for the manifestation of these properties. To that end, 21 A(H1N1)pdm09 influenza viruses were tested for their pathogenicity and toxicity in a mouse model with a ts/non-ts phenotype manifestation and HA thermal stability. The results demonstrated that, for a strain to have high pathogenicity, it must express a toxic effect, have a non-ts phenotype, and have a thermally stable HA. The ancestor A/California/07/2009 (H1N1)pdm influenza virus expressed the non-ts phenotype, after which the cycling trend of the ts/non-ts phenotype was observed in new strains of A(H1N1)pdm09 influenza viruses, indicating that the ratio of the ts phenotype will increase in the coming years. Of the 21 tested viruses, A/South Africa/3626/2013 had the high pathogenicity in the mouse model. Sequence alignment analysis showed that this virus has three unique mutations in the polymerase complex, two of which are in the PB2 gene and one that is in the PB1 gene. Further study of these mutations might explain the distinguishing pathogenicity.

Safety, Immunogenicity, and Protective Efficacy of an H5N1 Chimeric Cold-Adapted Attenuated Virus Vaccine in a Mouse Model

H5N1 influenza virus is a threat to public health worldwide. The virus can cause severe morbidity and mortality in humans. We constructed an H5N1 influenza candidate virus vaccine from the A/chicken/Guizhou/1153/2016 strain that was recommended by the World Health Organization. In this study, we designed an H5N1 chimeric influenza A/B vaccine based on a cold-adapted (ca) influenza B virus B/Vienna/1/99 backbone. We modified the ectodomain of H5N1 hemagglutinin (HA) protein, while retaining the packaging signals of influenza B virus, and then rescued a chimeric cold-adapted H5N1 candidate influenza vaccine through a reverse genetic system. The chimeric H5N1 vaccine replicated well in eggs and the Madin-Darby Canine Kidney cells. It maintained a temperature-sensitive and cold-adapted phenotype. The H5N1 vaccine was attenuated in mice. Hemagglutination inhibition (HAI) antibodies, micro-neutralizing (MN) antibodies, and IgG antibodies were induced in immunized mice, and the mucosal IgA antibody responses were detected in their lung lavage fluids. The IFN-γ-secretion and IL-4-secretion by the mouse splenocytes were induced after stimulation with the specific H5N1 HA protein. The chimeric H5N1 candidate vaccine protected mice against lethal challenge with a wild-type highly pathogenic avian H5N1 influenza virus. The chimeric H5 candidate vaccine is thus a potentially safe, attenuated, and reassortment-incompetent vaccine with circulating A viruses.

Immune Responses Elicited by Live Attenuated Influenza Vaccines as Correlates of Universal Protection against Influenza Viruses

Influenza virus infection remains a major public health challenge, causing significant morbidity and mortality by annual epidemics and intermittent pandemics. Although current seasonal influenza vaccines provide efficient protection, antigenic changes of the viruses often significantly compromise the protection efficacy of vaccines, rendering most populations vulnerable to the viral infection. Considerable efforts have been made to develop a universal influenza vaccine (UIV) able to confer long-lasting and broad protection. Recent studies have characterized multiple immune correlates required for providing broad protection against influenza viruses, including neutralizing antibodies, non-neutralizing antibodies, antibody effector functions, T cell responses, and mucosal immunity. To induce broadly protective immune responses by vaccination, various strategies using live attenuated influenza vaccines (LAIVs) and novel vaccine platforms are under investigation. Despite superior cross-protection ability, very little attention has been paid to LAIVs for the development of UIV. This review focuses on immune responses induced by LAIVs, with special emphasis placed on the breadth and the potency of individual immune correlates. The promising prospect of LAIVs to serve as an attractive and reliable vaccine platforms for a UIV is also discussed. Several important issues that should be addressed with respect to the use of LAIVs as UIV are also reviewed.

Genetic Basis of Attenuation of Cold-Adapted Influenza Strain B/Leningrad/14/17/55 - Backup Master Donor Virus for Influenza Type B Live Attenuated Vaccines

The reassortant vaccine strain of live attenuated influenza vaccine inherits temperature sensitivity and areactogenicity from cold-adapted attenuated master donor virus. In Russia, B/ USSR/60/69 master donor virus (B60) is currently in use for the preparation of live attenuated type B influenza vaccine candidates. Trivalent live attenuated influenza vaccine based on A/ Leningrad/134/17/57 and B60 are licensed for the use in Russia for single dose vaccination of adults and children over 3 years. B/Leningrad/14/17/55 (B14) cold-adapted virus is a backup master donor virus for live attenuated type B influenza vaccine. According to our preliminary estimates, it is more attenuated than B60, which can allow expanding applicability of this vaccine for children under 3 years of age. In this paper, the role of B14 genes in its attenuation was assessed. Representative collection of reassortants of B14 with epidemic influenza B viruses was obtained, a phenotypic analysis of reassortants was performed, and their pathogenicity for animals was assessed. The leading role of PB2 and PA genes in attenuation of B14 master donor virus was proven.

The human antibody response to influenza A virus infection and vaccination

The adaptive immune response to influenza virus infection is multifaceted and complex, involving antibody and cellular responses at both systemic and mucosal levels. Immune responses to natural infection with influenza virus in humans are relatively broad and long-lived, but influenza viruses can escape from these responses over time owing to their high mutation rates and antigenic flexibility. Vaccines are the best available countermeasure against infection, but vaccine effectiveness is low compared with other viral vaccines, and the induced immune response is narrow and short-lived. Furthermore, inactivated influenza virus vaccines focus on the induction of systemic IgG responses but do not effectively induce mucosal IgA responses. Here, I review the differences between natural infection and vaccination in terms of the antibody responses they induce and how these responses protect against future infection. A better understanding of how natural infection induces broad and long-lived immune responses will be key to developing next-generation influenza virus vaccines.

Sequential Immunization with Universal Live Attenuated Influenza Vaccine Candidates Protects Ferrets against a High-Dose Heterologous Virus Challenge

The development of universal influenza vaccines has been a priority for more than 20 years. We conducted a preclinical study in ferrets of two sets of live attenuated influenza vaccines (LAIVs) expressing chimeric hemagglutinin (cHA). These vaccines contained the HA stalk domain from H1N1pdm09 virus but had antigenically unrelated globular head domains from avian influenza viruses H5N1, H8N4 and H9N2. The viral nucleoproteins (NPs) in the two sets of universal LAIV candidates were from different sources: one LAIV set contained NP from A/Leningrad/17 master donor virus (MDV), while in the other set this gene was from wild-type (WT) H1N1pdm09 virus, in order to better match the CD8 T-cell epitopes of currently circulating influenza A viruses. To avoid any difference in protective effect of the various anti-neuraminidase (NA) antibodies, all LAIVs were engineered to contain the NA gene of Len/17 MDV. Naïve ferrets were sequentially immunized with three doses of (i) classical LAIVs containing non-chimeric HA and NP from MDV (LAIVs (NP-MDV)); (ii) cHA-based LAIVs containing NP from MDV (cHA LAIVs (NP-MDV)); and (iii) cHA-based LAIVs containing NP from H1N1pdm09 virus (cHA LAIVs (NP-WT)). All vaccination regimens were safe, producing no significant increase in body temperature or weight loss, in comparison with the placebo group. The two groups of cHA-based vaccines induced a broadly reactive HA stalk-directed antibody, while classical LAIVs did not. A high-dose challenge with H1N1pdm09 virus induced significant pathology in the control, non-immunized ferrets, including high virus titers in respiratory tissues, clinical signs of disease and histopathological changes in nasal turbinates and lung tissues. All three vaccination regimens protected animals from clinical manifestations of disease: immunized ferrets did not lose weight or show clinical symptoms, and their fever was significantly lower than in the control group. Further analysis of virological and pathological data revealed the following hierarchy in the cross-protective efficacy of the vaccines: cHA LAIVs (NP-WT) > cHA LAIVs (NP-MDV) > LAIVs (NP-MDV). This ferret study showed that prototype universal cHA-based LAIVs are highly promising candidates for further clinical development.

Experimental Study of Genetic Constellation of Cold-Adapted Master Donor Viruses for Live Attenuated Influenza Vaccine Type B

We studied the constellation of genes encoding polymerase complex proteins of master donor viruses for Russian live attenuated influenza vaccine type B. Reassortants of the reserve attenuation donor B/Leningrad/14/17/55 with B/USSR/60/69 master donor virus currently used for manufacturing seasonal influenza vaccine were prepared and examined. Most reassortants obtained by the classical reassortment method inherited all genes from the B/Leningrad/14/17/55 virus except the gene encoding PB1 subunit of the polymerase complex. One reassortant was selected for further evaluation of the role of PB1 gene. Greater attenuation of the strain for experimental animals (mice) in comparison with the original strains was demonstrated. This indicates high degree of constellation of genes of cold-adapted master donor viruses and the important compensating role of amino acid substitutions in the PB1 protein of B/Leningrad/14/17/55 donor virus in preventing viral hyperattenuation.

Temperature Sensitive Mutations in Influenza A Viral Ribonucleoprotein Complex Responsible for the Attenuation of the Live Attenuated Influenza Vaccine

Live attenuated influenza vaccines (LAIV) have prevented morbidity and mortality associated with influenza viral infections for many years and represent the best therapeutic option to protect against influenza viral infections in humans. However, the development of LAIV has traditionally relied on empirical methods, such as the adaptation of viruses to replicate at low temperatures. These approaches require an extensive investment of time and resources before identifying potential vaccine candidates that can be safely implemented as LAIV to protect humans. In addition, the mechanism of attenuation of these vaccines is poorly understood in some cases. Importantly, LAIV are more efficacious than inactivated vaccines because their ability to mount efficient innate and adaptive humoral and cellular immune responses. Therefore, the design of potential LAIV based on known properties of viral proteins appears to be a highly appropriate option for the treatment of influenza viral infections. For that, the viral RNA synthesis machinery has been a research focus to identify key amino acid substitutions that can lead to viral attenuation and their use in safe, immunogenic, and protective LAIV. In this review, we discuss the potential to manipulate the influenza viral RNA-dependent RNA polymerase (RdRp) complex to generate attenuated forms of the virus that can be used as LAIV for the treatment of influenza viral infections, one of the current and most effective prophylactic options for the control of influenza in humans.

Broadly protective anti-hemagglutinin stalk antibodies induced by live attenuated influenza vaccine expressing chimeric hemagglutinin

The development of influenza vaccines that can provide broad protection against all drifted seasonal virus variants, zoonotic infections and emerging pandemic strains, has been a priority for two decades. Here we propose a strategy of inducing broadly-reactive anti-stalk antibody by sequential immunizations with live attenuated influenza vaccines (LAIVs) expressing chimeric HAs (cHAs). These vaccines are designed to contain identical hemagglutinin stalk domains from H1N1 virus but antigenically unrelated globular head domains from avian influenza virus subtypes H5, H8 and H9. Mouse experiments demonstrated enhanced cross-protection of cHA-containing LAIVs compared to the relevant vaccine viruses expressing natural HAs, and this enhanced protection was driven by stalk-HA-reactive IgG antibodies. The establishment of fully functional cross-protective immunity after two doses of cHA LAIV vaccination in naïve animals suggests that a similar effect might be expected after a single cHA LAIV dose in primed individuals, or after two to three doses in naïve children.

Development of an Alternative Modified Live Influenza B Virus Vaccine

Influenza B virus (IBV) is considered a major human pathogen, responsible for seasonal epidemics of acute respiratory illness. Two antigenically distinct IBV hemagglutinin (HA) lineages cocirculate worldwide with little cross-reactivity. Live attenuated influenza virus (LAIV) vaccines have been shown to provide better cross-protective immune responses than inactivated vaccines by eliciting local mucosal immunity and systemic B cell- and T cell-mediated memory responses. We have shown previously that incorporation of temperature-sensitive (ts) mutations into the PB1 and PB2 subunits along with a modified HA epitope tag in the C terminus of PB1 resulted in influenza A viruses (IAV) that are safe and effective as modified live attenuated (att) virus vaccines (IAV att). We explored whether analogous mutations in the IBV polymerase subunits would result in a stable virus with an att phenotype. The PB1 subunit of the influenza B/Brisbane/60/2008 strain was used to incorporate ts mutations and a C-terminal HA tag. Such modifications resulted in a B/Bris att strain with ts characteristics in vitro and an att phenotype in vivo Vaccination studies in mice showed that a single dose of the B/Bris att candidate stimulated sterilizing immunity against lethal homologous challenge and complete protection against heterologous challenge. These studies show the potential of an alternative LAIV platform for the development of IBV vaccines.IMPORTANCE A number of issues with regard to the effectiveness of the LAIV vaccine licensed in the United States (FluMist) have arisen over the past three seasons (2013-2014, 2014-2015, and 2015-2016). While the reasons for the limited robustness of the vaccine-elicited immune response remain controversial, this problem highlights the critical importance of continued investment in LAIV development and creates an opportunity to improve current strategies so as to develop more efficacious vaccines. Our laboratory has developed an alternative strategy, the incorporation of 2 amino acid mutations and a modified HA tag at the C terminus of PB1, which is sufficient to attenuate the IBV. As a LAIV, this novel vaccine provides complete protection against IBV strains. The availability of attenuated IAV and IBV backbones based on contemporary strains offers alternative platforms for the development of LAIVs that may overcome current limitations.

Evaluation of a candidate live attenuated influenza vaccine prepared in Changchun BCHT (China) for safety and efficacy in ferrets

We evaluated the safety and efficacy of a live attenuated influenza vaccine (LAIV) product in ferrets. The BCHT LAIV product was significantly less virulent than wild-type H1N1 virus, when evaluated by comparing virus shedding and histopathologic lesions. The data indicated strong evidence for an attenuated phenotype of LAIV. Furthermore, the vaccine induced robust humoral immune responses in seronegative ferrets, and protected ferrets against development of fever, weight loss and turbinate inflammatory lesions after challenging with H3N2 wide-type influenza virus. Thus, the BCHT LAIV product was safe in healthy seronegative ferrets and protected ferrets against infection of H3N2 influenza virus.

Genetic analysis of attenuation markers of cold-adapted X-31 influenza live vaccine donor strain

Cold-adapted live attenuated influenza vaccines (CAIVs) have been considered as a safe prophylactic measure to prevent influenza virus infections. The safety of a CAIV depends largely on genetic markers that confer specific attenuation phenotypes. Previous studies with other CAIVs reported that polymerase genes were primarily responsible for the attenuation. Here, we analyzed the genetic mutations and their phenotypic contribution in the X-31 ca strain, a recently developed alternative CAIV donor strain. During the cold-adaptation of its parental X-31 virus, various numbers of sequence changes were accumulated in all six internal genes. Phenotypic analysis with single-gene and multiple-gene reassortant viruses suggests that NP gene makes the largest contribution to the cold-adapted (ca) and temperature-sensitive (ts) characters, while the remaining other internal genes also impart attenuation characters with varying degrees. A balanced contribution of all internal genes to the attenuation suggests that X-31 ca could serve as an ideal master donor strain for CAIVs preventing influenza epidemics and pandemics.

Genetic stability of live attenuated vaccines against potentially pandemic influenza viruses

BACKGROUND

Ensuring genetic stability is a prerequisite for live attenuated influenza vaccine (LAIV). This study describes the results of virus shedding and clinical isolates' testing of Phase I clinical trials of Russian LAIVs against potentially pandemic influenza viruses in healthy adults.

METHODS

Three live attenuated vaccines against potentially pandemic influenza viruses, H2N2 LAIV, H5N2 LAIV and H7N3 LAIV, generated by classical reassortment in eggs, were studied. For each vaccine tested, subjects were randomly distributed into two groups to receive two doses of either LAIV or placebo at a 3:1 vaccine/placebo ratio. Nasal swabs were examined for vaccine virus shedding by culturing in eggs and by PCR. Vaccine isolates were tested for temperature sensitivity and cold-adaptation (ts/ca phenotypes) and for nucleotide sequence.

RESULTS

The majority of nasal wash positive specimens were detected on the first day following vaccination. PCR method demonstrated higher sensitivity than routine virus isolation in eggs. None of the placebo recipients had detectable vaccine virus replication. All viruses isolated from the immunized subjects retained the ts/ca phenotypic characteristics of the master donor virus (MDV) and were shown to preserve all attenuating mutations described for the MDV. These data suggest high level of vaccine virus genetic stability after replication in humans. During manufacture process, no additional mutations occurred in the genome of H2N2 LAIV. In contrast, one amino acid change in the HA of H7N3 LAIV and two additional mutations in the HA of H5N2 LAIV manufactured vaccine lot were detected, however, they did not affect their ts/ca phenotypes.

CONCLUSIONS

Our clinical trials revealed phenotypic and genetic stability of the LAIV viruses recovered from the immunized volunteers. In addition, no vaccine virus was detected in the placebo groups indicating the lack of person-to-person transmission. LAIV TRIAL REGISTRATION at ClinicalTrials.gov: H7N3-NCT01511419; H5N2-NCT01719783; H2N2-NCT01982331.

Clinical testing of pre-pandemic live attenuated A/H5N2 influenza candidate vaccine in adult volunteers: results from a placebo-controlled, randomized double-blind phase I study

BACKGROUND

This study describes a double-blinded randomized placebo-controlled phase I clinical trial of A/H5N2 live attenuated influenza vaccine in healthy volunteers.

METHODS

Two doses of vaccine or placebo were administered intranasally to 30 and 10 subjects, respectively. Nasal swabs were examined for vaccine shedding and local antibody responses; serum samples were tested for binding, hemagglutinating and neutralizing antibodies and peripheral blood mononuclear cells were tested for cell-mediated immune responses.

RESULTS

The vaccine was well tolerated and not associated with increased rates of adverse events or the occurrence of serious adverse events. Influenza virus was detected in nasal swabs on the first day in the majority of volunteers (93%), while 17% of volunteers tested positive on the second, none on the third day or later following the first vaccination; lower frequency of shedding was observed after the second vaccination. The vaccine was immunogenic as assessed four weeks after the second dose, with 37.9% and 48.3% of subjects seroconverting by hemagglutination inhibition and neutralization assays, respectively. An immune response was observed in 96.6% subjects that received A/H5N2 LAIV in at least one of the assays conducted. None of the placebo recipients exhibited a response in any of the assays.

CONCLUSION

The A/H5N2 vaccine was safe, well tolerated, and immunogenic in healthy adults.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01719783.

Equine and Canine Influenza H3N8 Viruses Show Minimal Biological Differences Despite Phylogenetic Divergence

The A/H3N8 canine influenza virus (CIV) emerged from A/H3N8 equine influenza virus (EIV) around the year 2000 through the transfer of a single virus from horses to dogs. We defined and compared the biological properties of EIV and CIV by examining their genetic variation, infection, and growth in different cell cultures, receptor specificity, hemagglutinin (HA) cleavage, and infection and growth in horse and dog tracheal explant cultures. Comparison of sequences of viruses from horses and dogs revealed mutations that may be linked to host adaptation and tropism. We prepared infectious clones of representative EIV and CIV strains that were similar to the consensus sequences of viruses from each host. The rescued viruses, including HA and neuraminidase (NA) double reassortants, exhibited similar degrees of long-term growth in MDCK cells. Different host cells showed various levels of susceptibility to infection, but no differences in infectivity were seen when comparing viruses. All viruses preferred α2-3- over α2-6-linked sialic acids for infections, and glycan microarray analysis showed that EIV and CIV HA-Fc fusion proteins bound only to α2-3-linked sialic acids. Cleavage assays showed that EIV and CIV HA proteins required trypsin for efficient cleavage, and no differences in cleavage efficiency were seen. Inoculation of the viruses into tracheal explants revealed similar levels of infection and replication by each virus in dog trachea, although EIV was more infectious in horse trachea than CIV.

IMPORTANCE

Influenza A viruses can cross species barriers and cause severe disease in their new hosts. Infections with highly pathogenic avian H5N1 virus and, more recently, avian H7N9 virus have resulted in high rates of lethality in humans. Unfortunately, our current understanding of how influenza viruses jump species barriers is limited. Our aim was to provide an overview and biological characterization of H3N8 equine and canine influenza viruses using various experimental approaches, since the canine virus emerged from horses approximately 15 years ago. We showed that although there were numerous genetic differences between the equine and canine viruses, this variation did not result in dramatic biological differences between the viruses from the two hosts, and the viruses appeared phenotypically equivalent in most assays we conducted. These findings suggest that the cross-species transmission and adaptation of influenza viruses may be mediated by subtle changes in virus biology.

Influenza vaccines: from whole virus preparations to recombinant protein technology

Vaccination against influenza represents our most effective form of prevention. Historical approaches toward vaccine creation and production have yielded highly effective vaccines that are safe and immunogenic. Despite their effectiveness, these historical approaches do not allow for the incorporation of changes into the vaccine in a timely manner. In 2013, a recombinant protein-based vaccine that induces immunity toward the influenza virus hemagglutinin was approved for use in the USA. This vaccine represents the first approved vaccine formulation that does not require an influenza virus intermediate for production. This review presents a brief history of influenza vaccines, with insight into the potential future application of vaccines generated using recombinant technology.

Safety and immunogenicity in man of a cell culture derived trivalent live attenuated seasonal influenza vaccine: a Phase I dose escalating study in healthy volunteers

Live attenuated influenza vaccine (LAIV) offers the promise of inducing a variety of immune responses thereby conferring protection to circulating field strains. LAIVs are based on cold adapted and temperature sensitive phenotypes of master donor viruses (MDVs) containing the surface glycoprotein genes of seasonal influenza strains. Two types of MDV lineages have been described, the Ann Arbor lineages and the A/Leningrad/17 and B/USSR/60 lineages. Here the safety and immunogenicity of a Madin Darby Canine Kidney - cell culture based, intranasal LAIV derived from A/Leningrad/17 and B/USSR, was evaluated in healthy influenza non-naive volunteers 18-50 years of age. In a double-blind, randomized, placebo-controlled design, single escalating doses of 1×10(5), 1×10(6), or 1×10(7) tissue culture infectious dose 50% (TCID50) of vaccine containing each of the three influenza virus re-assortants recommended by the World Health Organization for the 2008-2009 season were administered intranasally. A statistically significant geometric mean increase in hemagglutination inhibition titer was reached for influenza strain A/H3N2 after immunization with all doses of LAIV. For the A/H1N1 and B strains, the GMI in HI titer did not increase for any of the doses. Virus neutralization antibody titers showed a similar response pattern. A dose-response effect could not be demonstrated for any of the strains, neither for the HI antibody nor for the VN antibody responses. No influenza like symptoms, no nasal congestions, no rhinorrhea, or other influenza related upper respiratory tract symptoms were observed. In addition, no difference in the incidence or nature of adverse events was found between vaccine and placebo treated subjects. Overall, the results indicated that the LAIV for nasal administration is immunogenic (i.e. able to provoke an immune response) and safe both from the perspective of the attenuated virus and the MDCK cell line from which it was derived, and it warrants further development.

Protective efficacy in mice of monovalent and trivalent live attenuated influenza vaccines in the background of cold-adapted A/X-31 and B/Lee/40 donor strains

Influenza virus continues to take a heavy toll on human health and vaccination remains the mainstay of efforts to reduce the clinical impact imposed by viral infections. Proven successful for establishing live attenuated vaccine donor strains, cold-adapted live attenuated influenza vaccines (CAIVs) have become an attractive modality for controlling the virus infection. Previously, we developed the cold-adapted strains A/X-31 and B/Lee/40 as novel donor strains of CAIVs against influenza A and B viruses. In this study, we investigated the protective immune responses of both mono- and trivalent vaccine formulations in the mouse model. Two type A vaccines and one type B vaccine against A/New Caledonia/20/99 (H1N1), A/Panama/2007/99 (H3N2), and B/Shangdong/7/97 in the background of the A/X-31 ca or B/Lee/40 ca were generated by a reassortment procedure and evaluated for their immunogenicity and protective efficacy. Each monovalent vaccine elicited high levels of serum antibodies and conferred complete protection against homologous wild type virus infection. As compared to the monovalent vaccines, trivalent formulation induced higher levels of type A-specific serum antibodies and slightly lower levels of type B-specific antibodies, suggesting an immunological synergism within type A viruses and an interference in the replication of type B virus. Relatively lower type B-specific immunogenicity in trivalent vaccine formulation could be effectively implemented by increasing the vaccine dose of influenza B virus. These results of immunogenicity, protection efficacy, and immunological synergism between type A vaccines provide an experimental basis for optimal composition of trivalent vaccines for subsequent developments of multivalent CAIVs against seasonal and pandemic influenza viruses.

The new temperature-sensitive mutation PA-F35S for developing recombinant avian live attenuated H5N1 influenza vaccine

BACKGROUND

H5N1 highly pathogenic avian influenza virus (HPAIV) is continuously circulating in many Asian countries and threatening poultry industry and human population. Vaccination is the best strategy to control H5N1 HPAIV infection in poultry and transmission to human population. The aim of this study is to identify new temperature-sensitive (ts) mutations for developing recombinant avian live attenuated H5N1 influenza vaccine.

FINDINGS

A "6 + 2" recombinant virus C4/W1 that contained NA gene and modified HA gene from virus A/chicken/Hubei/327/2004 (H5N1) (C4), and six internal genes from virus A/duck/Hubei/W1/2004 (H9N2) (W1) was generated using reverse genetics and subsequently passaged in chicken eggs at progressively lower temperatures (32°C, 28°C and 25°C). The resulting virus acquired ts phenotype and one of its amino acid mutations, PA (F35S), was identified as ts mutation. Furthermore, when used as live attenuated vaccine, the recombinant virus with this ts mutation PA (F35S) provided efficient protection for chickens against H5N1 HPAIV infection.

CONCLUSIONS

These findings highlight the potential of the new ts mutation PA (F35S) in developing recombinant avian live attenuated H5N1 influenza vaccine.

Artificial hybrids of influenza A virus RNA polymerase reveal PA subunit modulates its thermal sensitivity

BACKGROUND

Influenza A virus can infect a variety of different hosts and therefore has to adapt to different host temperatures for its efficient viral replication. Influenza virus codes for an RNA polymerase of 3 subunits: PB1, PB2 and PA. It is well known that the PB2 subunit is involved in temperature sensitivity, such as cold adaptation. On the other hand the role of the PA subunit in thermal sensitivity is still poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

To test which polymerase subunit(s) were involved in thermal stress we reconstituted artificial hybrids of influenza RNA polymerase in ribonucleoprotein (RNP) complexes and measured steady-state levels of mRNA, cRNA and vRNA at different temperatures. The PA subunit was involved in modulating RNP activity under thermal stress. Residue 114 of the PA subunit was an important determinant of this activity.

CONCLUSIONS/SIGNIFICANCE

These findings suggested that influenza A virus may acquire an RNA polymerase adapted to different body temperatures of the host by reassortment of the RNA polymerase genes.