Recombinant cold-adapted attenuated influenza A vaccines for use in children: reactogenicity and antigenic activity of cold-adapted recombinants and analysis of isolates from the vaccinees

Safety, immunogenicity and infectivity of new live attenuated influenza vaccines

Live attenuated influenza vaccines (LAIVs) are believed to be immunologically superior to inactivated influenza vaccines, because they can induce a variety of adaptive immune responses, including serum antibodies, mucosal and cell-mediated immunity. In addition to the licensed cold-adapted LAIV backbones, a number of alternative LAIV approaches are currently being developed and evaluated in preclinical and clinical studies. This review summarizes recent progress in the development and evaluation of LAIVs, with special attention to their safety, immunogenicity and infectivity for humans, and discusses their perspectives for the future.

Principles underlying rational design of live attenuated influenza vaccines

Despite recent innovative advances in molecular virology and the developments of vaccines, influenza virus remains a serious burden for human health. Vaccination has been considered a primary countermeasure for prevention of influenza infection. Live attenuated influenza vaccines (LAIVs) are particularly attracting attention as an effective strategy due to several advantages over inactivated vaccines. Cold-adaptation, as a classical means for attenuating viral virulence, has been successfully used for generating safe and effective donor strains of LAIVs against seasonal epidemics and occasional pandemics. Recently, the advent of reverse genetics technique expedited a variety of rational strategies to broaden the pool of LAIVs. Considering the breadth of antigenic diversity of influenza virus, the pool of LAIVs is likely to equip us with better options for controlling influenza pandemics. With a brief reflection on classical attenuating strategies used at the initial stage of development of LAIVs, especially on the principles underlying the development of cold-adapted LAIVs, we further discuss and outline other attenuation strategies especially with respect to the rationales for attenuation, and their practicality for mass production. Finally, we propose important considerations for a rational vaccine design, which will provide us with practical guidelines for improving the safety and effectiveness of LAIVs.

Contribution of antibody production against neuraminidase to the protection afforded by influenza vaccines

Vaccines are instrumental in controlling the burden of influenza virus infection in humans and animals. Antibodies raised against both major viral surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), can contribute to protective immunity. Vaccine-induced HA antibodies have been characterized extensively, and they generally confer protection by blocking the attachment and fusion of a homologous virus onto host cells. Although not as well characterized, some functions of NA antibodies in influenza vaccine-mediated immunity have been recognized for many years. In this review, we summarize the case for NA antibodies in influenza vaccine-mediated immunity. In the absence of well-matched HA antibodies, NA antibodies can provide varying degrees of protection against disease. NA proteins of seasonal influenza vaccines have been shown in some instances to elicit serum antibodies with cross-reactivity to avian-origin and swine-origin influenza strains, in addition to HA drift variants. NA-mediated immunity has been linked to (i) conserved NA epitopes amongst otherwise antigenically distinct strains, partly attributable to the segmented influenza viral genome; (ii) inhibition of NA enzymatic activity; and (iii) the NA content in vaccine formulations. There is a potential to enhance the effectiveness of existing and future influenza vaccines by focusing greater attention on the antigenic characteristics and potency of the NA protein.

Comparative safety, immunogenicity, and efficacy of several anti-H5N1 influenza experimental vaccines in a mouse and chicken models (Testing of killed and live H5 vaccine)

Please cite this paper as: Gambaryan et al. (2011) Comparative safety, immunogenicity, and efficacy of several anti‐H5N1 influenza experimental vaccines in a mouse and chicken models. Parallel testing of killed and live H5 vaccine. Influenza and Other Respiratory Viruses 6(3), 188–195.

Objective  Parallel testing of inactivated (split and whole virion) and live vaccine was conducted to compare the immunogenicity and protective efficacy against homologous and heterosubtypic challenge by H5N1 highly pathogenic avian influenza virus.

Method  Four experimental live vaccines based on two H5N1 influenza virus strains were tested; two of them had hemagglutinin (HA) of A/Vietnam/1203/04 strain lacking the polybasic HA cleavage site, and two others had hemagglutinins from attenuated H5N1 virus A/Chicken/Kurgan/3/05, with amino acid substitutions of Asp54/Asn and Lys222/Thr in HA1 and Val48/Ile and Lys131/Thr in HA2 while maintaining the polybasic HA cleavage site. The neuraminidase and non‐glycoprotein genes of the experimental live vaccines were from H2N2 cold‐adapted master strain A/Leningrad/134/17/57 (VN‐Len and Ku‐Len) or from the apathogenic H6N2 virus A/Gull/Moscow/3100/2006 (VN‐Gull and Ku‐Gull). Inactivated H5N1 and H1N1 and live H1N1 vaccine were used for comparison. All vaccines were applied in a single dose. Safety, immunogenicity, and protectivity against the challenge with HPAI H5N1 virus A/Chicken/Kurgan/3/05 were estimated.

Results  All experimental live H5 vaccines tested were apathogenic as determined by weight loss and conferred more than 90% protection against lethal challenge with A/Chicken/Kurgan/3/05 infection. Inactivated H1N1 vaccine in mice offered no protection against challenge with H5N1 virus, while live cold‐adapted H1N1 vaccine reduced the mortality near to zero level.

Conclusions  The high yield, safety, and protectivity of VN‐Len and Ku‐Len made them promising strains for the production of inactivated and live vaccines against H5N1 viruses.

A pandemic influenza H1N1 live vaccine based on modified vaccinia Ankara is highly immunogenic and protects mice in active and passive immunizations

Background

The development of novel influenza vaccines inducing a broad immune response is an important objective. The aim of this study was to evaluate live vaccines which induce both strong humoral and cell-mediated immune responses against the novel human pandemic H1N1 influenza virus, and to show protection in a lethal animal challenge model.

Methodology/Principal Findings

For this purpose, the hemagglutinin (HA) and neuraminidase (NA) genes of the influenza A/California/07/2009 (H1N1) strain (CA/07) were inserted into the replication-deficient modified vaccinia Ankara (MVA) virus - a safe poxviral live vector – resulting in MVA-H1-Ca and MVA-N1-Ca vectors. These live vaccines, together with an inactivated whole virus vaccine, were assessed in a lung infection model using immune competent Balb/c mice, and in a lethal challenge model using severe combined immunodeficient (SCID) mice after passive serum transfer from immunized mice. Balb/c mice vaccinated with the MVA-H1-Ca virus or the inactivated vaccine were fully protected from lung infection after challenge with the influenza H1N1 wild-type strain, while the neuraminidase virus MVA-N1-Ca induced only partial protection. The live vaccines were already protective after a single dose and induced substantial amounts of neutralizing antibodies and of interferon-γ-secreting (IFN-γ) CD4- and CD8 T-cells in lungs and spleens. In the lungs, a rapid increase of HA-specific CD4- and CD8 T cells was observed in vaccinated mice shortly after challenge with influenza swine flu virus, which probably contributes to the strong inhibition of pulmonary viral replication observed. In addition, passive transfer of antisera raised in MVA-H1-Ca vaccinated immune-competent mice protected SCID mice from lethal challenge with the CA/07 wild-type virus.

Conclusions/Significance

The non-replicating MVA-based H1N1 live vaccines induce a broad protective immune response and are promising vaccine candidates for pandemic influenza.

Immunization with live influenza viruses in an experimental model of allergic bronchial asthma: infection and vaccination

BACKGROUND

Asthmatics in particular have a need for influenza vaccines because influenza infection is a frequent cause of hospitalization of patients with bronchial asthma. Currently, only inactivated influenza vaccines are recommended for influenza prevention in asthma sufferers.

OBJECTIVE

The aim of our study was to analyze and compare the effects of influenza infection and vaccination with live attenuated influenza vaccine (LAIV) on different phases of experimental murine allergic bronchial asthma (acute asthma and remission phase) and on subsequent exposure to allergen in sensitized animals.

METHODS

Ovalbumin (OVA)-specific serum IgE levels, IL-4 production by spleen and lung lymphocytes, and histological changes in the lungs of mice infected with pathogenic virus or LAIV were studied at two phases of OVA-induced bronchial asthma (acute asthma and remission). Results Infection with pathogenic virus both in acute asthma and remission led to asthma exacerbation associated with the production of OVA-specific IgE, IL-4 and significant inflammatory infiltration in airways. Infection, even after complete virus clearance, induced the aggravation of lung inflammation and IgE production in asthmatic mice additionally exposed to OVA. Immunization with LAIV at remission did not enhance allergic inflammatory changes in the lung, OVA-specific IgE or IL-4 production. Then after additional OVA exposure, histological and immunological changes in these mice were the same as in the control group.

CONCLUSIONS

Influenza infection provokes asthma exacerbation regardless of the disease phase. Immunization with LAIV during the remission phase of bronchial asthma is safe and does not interfere upon subsequent contact of asthma sufferers with allergen.

Genetic characterization and protective immunity of cold-adapted attenuated avian H9N2 influenza vaccine

H9N2 influenza viruses are endemic in many Asian countries including China and Korea, and cause a considerable economic loss to chicken industry by reduction in egg production and about 30% mortality. Here we developed live cold-adapted attenuated H9N2 influenza vaccine by adaptation of viruses in hen's eggs at 25 degrees C. Genetic analysis shows that the cold-adapted H9N2 (A/Chicken/Korea/S1/03) viruses contain a total of 44 amino acid substitutions, of which 7 amino acids are identical to the loci identified in the cold-adapted H2N2 (A/Ann Arbor/6/60) vaccine strain compared to genes in wild-type H9N2 (A/Chicken/Korea/S1/03) influenza viruses. When cold-adapted H9N2 (A/Chicken/Korea/S1/03) influenza viruses were inoculated in layers viruses were detectable in the tracheas, not in the lungs, no reduction of egg production and mortality was observed in contrast to the infection of wild-type H9N2 influenza viruses, and CD8+ T lymphocytes expressing IFN-gamma were induced. When layers vaccinated with cold-adapted attenuated H9N2 (A/Chicken/Korea/S1/03) influenza viruses were challenged with wild-type H9N2 (A/Chicken/Korea/521/04) influenza viruses, they were protected from the loss of egg production and mortality. Our results suggest that cold-adapted attenuated H9N2 vaccine can be used for controlling the infection of H9N2 influenza viruses in chickens.

Characterization of live influenza vaccine donor strain derived from cold-adaptation of X-31 virus

A human influenza A virus X-31 (high-yielding strain) was cold-adapted for possible future use as live attenuated vaccine. Mutant influenza viruses were selected during successive serial passage in embryonated hens' eggs at progressively lower sub-optimal temperature (30, 27 degrees C followed by 24 degrees C). The cold-passaged mutant exhibited both temperature-sensitivity (ts) and cold-adapted (ca) phenotypes. The pathogenicity and immunogenicity of X-31 ca virus were studied in mice following intranasal inoculation. The mice did not show clinical signs even at high titer infection. Immunization of mice with X-31 ca virus elicited high titers of neutralizing antibody and provided complete protection against homologous and heterologous virus challenges. To assess the genetic stability, the X-31 ca virus was passaged at 37 degrees C in MDCK cells or inoculated into mice. Revertant virus was not found in the lungs of any of the mice and the supernatants of the MDCK culture. We conclude that the X-31 ca candidate vaccine virus exhibits the desired level of attenuation, immunogenicity, and protective efficacy required for live attenuated vaccine and merits further evaluation at clinical level.

The HA1 of cold-adapted influenza B vaccine is not altered during replication in human vaccinees

Influenza viruses recovered from 14 children 2-10 days after vaccination with an egg-grown, cold-adapted influenza B vaccine (B/AA/1/86) were analyzed. Hemagglutination-inhibition (HI) assays using monoclonal antibodies did not detect antigenic differences between the vaccine strain and the viruses recovered from the vaccinees. Furthermore, nucleotide sequence analysis of the HA1 region did not reveal any changes compared to the sequence of the vaccine strain. These findings indicate that influenza B vaccine hemagglutinin is genetically stable during replication in human vaccinees.

Comparison of live attenuated and inactivated influenza vaccines in schoolchildren in Russia: I. Safety and efficacy in two Moscow schools, 1987/88

The performance of two doses of cold-adapted live attenuated vaccine versus one dose of whole-virus inactivated vaccine was compared in 8-15-year-old schoolchildren in two schools in Moscow, Russia, during the winter of 1987/88. Both vaccines gave rise to low frequencies of associated febrile or systemic reactions, but the inactivated vaccine, delivered by jet injector, did cause small local reactions in about half of the children. Immunogenicity was higher for both vaccines in antibody-free children, and higher levels of serum antibody were detected following use of inactivated vaccine. During the winter, influenza A (H3N2) and influenza B viruses circulated in Moscow. A clear outbreak of (H3N2) virus occurred in both schools, and infections with type B virus also occurred in one school. The influenza A/Philippines/2/82 (H3N2) component of both vaccines exhibited protective efficacy of about 40% (p < 0.05) against serologically proven infection caused by the antigenically drifted A/Sichuan/2/87 (H3N2)-like epidemic viruses in one school. In another school where illnesses associated with antibody rise were documented, efficacy was seen for both vaccines in reduction of illnesses, and of illnesses with serological evidence of infection, but statistical significance was not achieved.

Sequence changes in the live attenuated, cold-adapted variants of influenza A/Leningrad/134/57 (H2N2) virus

Nucleotide sequences were determined for the RNA segments coding for proteins other than the hemagglutinin and neuraminidase of the A/Leningrad/134/57 (H2N2) wild-type (A/Len/wt) virus and its two cold-adapted (ca) and attenuated variants, A/Leningrad/134/17/57 (A/Len/17/ca) and A/Leningrad/134/47/57 (A/Len/47/ca) that are used in the U.S.S.R. in the preparation of reassortant live attenuated vaccines. Ten nucleotide differences were detected between the sequences of the A/Len/wt and A/Len/17/ca viruses; of these, eight were deduced to encode amino acid (aa) substitutions. One aa substitution each was predicted for the PB2, M1, M2, and NS2 proteins, whereas two aa substitutions each were predicted for the PB1, and PA proteins of the A/Len/17/ca virus. Four additional nucleotide changes were found in the genome of the A/Len/47/ca virus; three of these were detected to code for one additional aa substitution each for the PB2, PB1, and NP proteins.

Development and characterization of cold-adapted viruses for use as live virus vaccines

Representative viruses from twelve RNA and two DNA virus genera have been successfully adapted to growth at sub-optimal temperature (cold-adapted). In almost every case, there was a correlation between acquisition of the cold-adaptation phenotype and loss of virulence in the normal host whether animal or man. Overall, the best method of cold adaptation to develop a live virus vaccine line appeared to be a stepwise lowering of the growth temperature allowing time for multiple lesions to occur and/or be selected. In addition, the starting virus should be a recent isolate not as yet adapted to a tissue culture host and the cold-adaptation process should then occur in a host heterologous to the virus' normal host. These viruses have been reviewed in the light of their cold-adaptation method and successful production of an attenuated line as virus vaccine candidate. Finally, detailed information is presented for the cold-adaptation process in influenza virus.

Recombinant cold-adapted attenuated influenza A vaccines for use in children: molecular genetic analysis of the cold-adapted donor and recombinants

A previously described cold-adapted attenuated virus, A/Leningrad/134/17/57 (H2N2), was further modified by 30 additional passages in chicken embryos at 25 degrees C. This virus had a distinct temperature-sensitive (ts) phenotype, grew well in chicken embryos at 25 degrees C, and failed to recombine with reference ts mutants of fowl plague virus containing ts lesions in five genes coding for non-glycosylated proteins (genes 1, 2, 5, 7, and 8). Recombination of A/Leningrad/134/47/57 with wild-type influenza virus strains A/Leningrad/322/79 (H1N1) and A/Bangkok/1/79(H3N2) yielded ts recombinants 47/25/1(H1N1) and 47/7/2 (H3N2). These recombinants inherited their ts phenotype and ability to reproduce in chicken embryos at 25 degrees C from the cold-adapted parent. Analysis of the genome composition of the recombinants obtained by recombination of the cold-adapted donor with wild-type influenza virus strains A/Leningrad/322/79(H1N1) and A/Bangkok/1/79(H3N2) showed that recombinants 47/25/1(H1N1) and 47/7/2 (H3N2) inherited five and six genes, respectively, from the cold-adapted parent, and hemagglutinin and neuraminidase genes from the wild-type strains.