Richard Fritz

A Tick-borne Encephalitis Virus Vaccine Based on the European Prototype Strain Induces Broadly Reactive Cross-neutralizing Antibodies in Humans

After vaccination of humans with tick-borne encephalitis virus (TBEV) vaccine, the extent of cross-neutralization between viruses of the European, Far Eastern, and Siberian subtypes of TBEV and Omsk hemorrhagic fever virus (OHFV) was analyzed. Hybrid viruses that encode the TBEV surface proteins for representative viruses within all subtypes, and OHFV, were constructed using the West Nile virus (WNV) backbone as vector. These viruses allow for unbiased head-to-head comparison in neutralization assays because they exhibit the antigenic characteristics of the TBEV strains from which the surface proteins were derived and showed equivalent biologic properties in cell culture. Human serum samples derived from a TBEV vaccine trial were analyzed and revealed comparable neutralizing antibody titers against European, Far Eastern, and Siberian subtype viruses, indicating equally potent cross-protection against these TBEV strains and a somewhat reduced but still protective neutralization capacity against more distantly related viruses, such as OHFV.

A Vero Cell–Derived Whole-Virus H5N1 Vaccine Effectively Induces Neuraminidase-Inhibiting Antibodies

A Vero cell-derived whole-virus H5N1 influenza vaccine has been shown to induce neutralizing antibodies directed against the hemagglutinin (HA) protein of diverse H5N1 strains in animal studies and clinical trials. However, neuraminidase-inhibiting (NAi) antibodies can reduce viral spread and may be of particular importance in the event of an H5N1 pandemic, where immunity due to HA antibodies is likely absent in the general population. Here we demonstrate the effective induction of NAi antibody titers after H5N1 vaccination in humans. In contrast to the immune response directed toward HA, a single vaccine dose induced a strong NAi response that was not significantly boosted by a second dose, most probably due to priming by previous vaccination or infection with seasonal influenza viruses. After 2 immunizations, seroconversion rates based on antibody titers against HA and NA were similar, indicating the induction of equally strong immune responses against both proteins by this H5N1 vaccine.

Quantitative comparison of the cross-protection induced by tick-borne encephalitis virus vaccines based on European and Far Eastern virus subtypes

Tick-borne encephalitis virus (TBEV) is a flavivirus of wide geographic distribution and the causative agent of tick-borne encephalitis (TBE), an infection of the central nervous system. TBE has the highest incidence rate in Russia, where locally produced as well as Western European vaccines for the prevention of TBE are available. The Western European vaccines are based on TBE viruses that belong to the European subtype, while the Russian vaccines are based on Far Eastern subtype viruses. The question of to which extent vaccination with a vaccine based on the European subtype is effective in protecting against the heterologous Far Eastern virus subtype - and vice versa - has not been answered conclusively. Here we immunized mice with TBE vaccines based on European and Far Eastern subtype viruses, and used an unbiased hybrid virus test system to determine cross-neutralizing antibody titers and cross-protective efficacy. All vaccines tested elicited cross-protective responses against the heterologous strains, similar to those induced against the respective homologous vaccine strains. These data, therefore, fully support the use of TBE vaccines in geographic regions where virus subtypes heterologous to the vaccine strains are prevalent.

Safety and Immunogenicity of a Vero Cell Culture–Derived Whole-Virus Influenza A(H5N1) Vaccine in a Pediatric Population

BACKGROUND Children are highly vulnerable to infection with novel influenza viruses. It is essential to develop candidate pandemic influenza vaccines that are safe and effective in the pediatric population. METHODS Infants and children aged 6-35 months and 3-8 years, respectively, were randomized to receive 2 immunizations with a 7.5-µg or 3.75-µg hemagglutinin (HA) dose of a nonadjuvanted whole-virus A/Vietnam(H5N1) vaccine; adolescents aged 9-17 years received a 7.5-µg dose only. A subset of participants received a booster immunization with an A/Indonesia(H5N1) vaccine approximately 1 year later. HA and neuraminidase antibody responses were assessed. RESULTS Vaccination was safe and well tolerated; adverse reactions were transient and predominantly mild. Two immunizations with the 7.5-µg dose of A/Vietnam vaccine induced virus microneutralization (MN) titers of ≥1:20 against the A/Vietnam strain in 68.8%-85.4% of participants in the different age groups. After the booster, 93.1%-100% of participants achieved MN titers of ≥1:20 against the A/Vietnam and A/Indonesia strains. Neuraminidase-inhibiting antibodies were induced in ≥90% of participants after 2 immunizations with the 7.5 µg A/Vietnam vaccine and in 100% of participants after the booster. CONCLUSIONS A whole-virus influenza A(H5N1) vaccine is suitable for prepandemic or pandemic immunization in a pediatric population. CLINICAL TRIALS REGISTRATION NCT01052402.

Immunogenicity and Protective Efficacy of a Vero Cell Culture-Derived Whole-Virus H7N9 Vaccine in Mice and Guinea Pigs

Background A novel avian H7N9 virus with a high case fatality rate in humans emerged in China in 2013. We evaluated the immunogenicity and protective efficacy of a candidate Vero cell culture-derived whole-virus H7N9 vaccine in small animal models. Methods Antibody responses induced in immunized DBA/2J mice and guinea pigs were evaluated by hemagglutination inhibition (HI), microneutralization (MN), and neuraminidase inhibition (NAi) assays. T-helper cell responses and IgG subclass responses in mice were analyzed by ELISPOT and ELISA, respectively. Vaccine efficacy against lethal challenge with wild-type H7N9 virus was evaluated in immunized mice. H7N9-specific antibody responses induced in mice and guinea pigs were compared to those induced by a licensed whole-virus pandemic H1N1 (H1N1pdm09) vaccine. Results The whole-virus H7N9 vaccine induced dose-dependent H7N9-specific HI, MN and NAi antibodies in mice and guinea pigs. Evaluation of T-helper cell responses and IgG subclasses indicated the induction of a balanced Th1/Th2 response. Immunized mice were protected against lethal H7N9 challenge in a dose-dependent manner. H7N9 and H1N1pdm09 vaccines were similarly immunogenic. Conclusions The induction of H7N9-specific antibody and T cell responses and protection against lethal challenge suggest that the Vero cell culture-derived whole-virus vaccine would provide an effective intervention against the H7N9 virus.

Safety and Immunogenicity of a Vero Cell Culture-Derived Whole-Virus H5N1 Influenza Vaccine in Chronically Ill and Immunocompromised Patients

ABSTRACT The development of vaccines against H5N1 influenza A viruses is a cornerstone of pandemic preparedness. Clinical trials of H5N1 vaccines have been undertaken in healthy subjects, but studies in risk groups have been lacking. In this study, the immunogenicity and safety of a nonadjuvanted cell culture-derived whole-virus H5N1 vaccine were assessed in chronically ill and immunocompromised adults. Subjects received two priming immunizations with a clade 1 A/Vietnam H5N1 influenza vaccine, and a subset also received a booster immunization with a clade 2.1 A/Indonesia H5N1 vaccine 12 to 24 months later. The antibody responses in the two populations were assessed by virus neutralization and single radial hemolysis assays. The T-cell responses in a subset of immunocompromised patients were assessed by enzyme-linked immunosorbent spot assay (ELISPOT). The priming and the booster vaccinations were safe and well tolerated in the two risk populations, and adverse reactions were predominantly mild and transient. The priming immunizations induced neutralizing antibody titers of ≥1:20 against the A/Vietnam strain in 64.2% of the chronically ill and 41.5% of the immunocompromised subjects. After the booster vaccination, neutralizing antibody titers of ≥1:20 against the A/Vietnam and A/Indonesia strains were achieved in 77.5% and 70.8%, respectively, of chronically ill subjects and in 71.6% and 67.5%, respectively, of immunocompromised subjects. The T-cell responses against the two H5N1 strains increased significantly over the baseline values. Substantial heterosubtypic T-cell responses were elicited against the 2009 pandemic H1N1 virus and seasonal A(H1N1), A(H3N2), and B subtypes. There was a significant correlation between T-cell responses and neutralizing antibody titers. These data indicate that nonadjuvanted whole-virus cell culture-derived H5N1 influenza vaccines are suitable for immunizing chronically ill and immunocompromised populations. (This study is registered at ClinicalTrials.gov under registration no. NCT00711295.)

A cell culture-derived whole-virus H9N2 vaccine induces high titer antibodies against hemagglutinin and neuraminidase and protects mice from severe lung pathology and weight loss after challenge with a highly virulent H9N2 isolate

BACKGROUND Influenza viruses of subtype A/H9N2 are enzootic in poultry across Asia and the Middle East and are considered to have pandemic potential. The development of new vaccine manufacturing technologies is a cornerstone of influenza pandemic preparedness. METHODS A non-adjuvanted whole-virus H9N2 vaccine was developed using Vero cell culture manufacturing technology. The induction of hemagglutination inhibition (HI) and virus-neutralizing antibodies was assessed in CD1 mice and guinea pigs. A highly sensitive enzyme-linked lectin assay was used to investigate the induction of antibodies capable of inhibiting the enzymatic activity of the H9N2 neuraminidase. Protective efficacy against virus replication in the lung after challenge with the homologous virus was evaluated in BALB/c mice by a TCID(50) assay, and prevention of virus replication in the lung and associated pathology were evaluated by histology and immunohistochemistry. To investigate the ability of the vaccine to prevent severe disease, BALB/c mice were challenged with a highly virulent mouse-adapted H9N2 isolate which was generated by multiple lung-to-lung passage of wild-type virus. RESULTS The vaccine elicited high titers of functional H9N2-specific HA antibodies in both mice and guinea pigs, as determined by HI and virus neutralization assays. High titer H9N2-specific neuraminidase inhibiting (NAi) antibodies were also induced in both species. Vaccinated mice were protected from lung virus replication in a dose-dependent manner after challenge with the homologous H9N2 virus. Immunohistochemical analyses confirmed the lack of virus replication in the lung and an associated substantial reduction in lung pathology. Dose-dependent protection from severe weight loss was also provided after challenge with the highly virulent mouse-adapted H9N2 virus. CONCLUSIONS The induction of high titers of H9N2-specific HI, virus-neutralizing and NAi antibodies and dose-dependent protection from virus replication and severe disease in animal models suggest that the Vero cell culture-derived whole-virus vaccine will provide an effective intervention in the event of a H9N2 pandemic situation.

Molecular Basis of the Divergent Immunogenicity of Two Pediatric Tick-Borne Encephalitis Virus Vaccines

ABSTRACT Studies evaluating the immunogenicity of two pediatric tick-borne encephalitis virus (TBEV) vaccines have reported contradictory results. These vaccines are based on two different strains of the European TBEV subtype: FSME-Immun Junior is based on the Neudörfl (Nd) strain, whereas Encepur Children is based on the Karlsruhe (K23) strain. The antibody (Ab) response induced by these two vaccines might be influenced by antigenic differences in the envelope (E) protein, which is the major target of neutralizing antibodies. We used an established hybrid virus assay platform to compare the levels of induction of neutralizing antibodies against the two vaccine virus strains in children aged 1 to 11 years who received two immunizations with FSME-Immun Junior or Encepur Children. The influence of amino acid differences between the E proteins of the Nd and K23 vaccine strains was investigated by mutational analyses and three-dimensional computer modeling. FSME-Immun Junior induced 100% seropositivity and similar neutralizing antibody titers against hybrid viruses containing the TBEV E protein of the two vaccine strains. Encepur Children induced 100% seropositivity only against the hybrid virus containing the E protein of the homologous K23 vaccine strain. Antibody responses induced by Encepur Children to the hybrid virus containing the E protein of the heterologous Nd strain were substantially and significantly (P < 0.001) lower than those to the K23 vaccine strain hybrid virus. Structure-based mutational analyses of the TBEV E protein indicated that this is due to a mutation in the DI-DII hinge region of the K23 vaccine strain E protein which may have occurred during production of the vaccine seed virus and which is not present in any wild-type TBE viruses. IMPORTANCE Our data suggest that there are major differences in the abilities of two European subtype pediatric TBEV vaccines to induce antibodies capable of neutralizing heterologous TBEV strains. This is a result of a mutation in the DI-DII hinge region of the E protein of the K23 vaccine virus strain used to manufacture Encepur Children which is not present in the Nd strain used to manufacture FSME-Immun Junior or in any other known naturally occurring TBEVs.

Neuraminidase-inhibiting antibody response to H5N1 virus vaccination in chronically ill and immunocompromised patients

Neuraminidase-inhibiting (NAi) antibodies have been reported to be an independent correlate of protection from influenza disease, but the NAi antibody response to influenza vaccination has never been assessed in chronically ill or immunocompromised participants. Using an enzyme-linked lectin assay, we demonstrated that 2 immunizations with a Vero cell culture-derived, whole-virus H5N1 A/Vietnam vaccine induces NAi antibodies in 94.3% of chronically ill and 83.8% of immunocompromised participants. A booster with a heterologous A/Indonesia H5N1 vaccine induced comparable NAi antibody titers in both groups and resulted in 100% seropositivity. These data support prepandemic H5N1 vaccination strategies for these highly vulnerable risk groups.