Potency determination of inactivated H7 influenza vaccines using monoclonal antibody-based ELISA and biolayer interferometry assays.

BACKGROUND: The single radial immunodiffusion (SRID) assay, the accepted method for determining potency of inactivated influenza vaccines, measures an immunogenic form of the influenza hemagglutinin. Nevertheless, alternative methods for measuring vaccine potency have been explored to address some of the weaknesses of the SRID assay, including limited sensitivity and the requirement for large amounts of standardized reagents. Monoclonal antibody (mAb)-based potency assays also have the ability to detect and measure relevant immunogenic forms of HA. OBJECTIVES: The objective of this study was to continue evaluation of mAb-based alternative methods for measuring the potency of inactivated influenza vaccines, focusing on A(H7N9) pandemic influenza vaccines. METHODS: Several murine mAbs that recognize different epitopes on the H7 hemagglutinin (HA) were identified and characterized. These mAbs were evaluated in both a mAb-capture ELISA and a mAb-based biolayer interferometry (BLI) assay. RESULTS: Results indicated that potency of inactivated A(H7N9) vaccines, including vaccine samples that were stressed by heat treatment, measured by either alternative method correlated well with potency determined by the traditional SRID potency assay. CONCLUSIONS: The availability of multiple H7 mAbs, directed to different HA epitopes, provides needed redundancy in the potency analysis as A(H7N9) viruses continue to evolve antigenically and suggests the importance of having a broad, well-characterized panel of mAbs available for development of vaccines against influenza strains with pandemic potential. In addition, the results highlight the potential of mAb-based platform such as ELISA and BLI for development as alternative methods for determining the potency of inactivated influenza vaccines.

A monoclonal antibody-based immunoassay for measuring the potency of 2009 pandemic influenza H1N1 vaccines.

BACKGROUND: The potency of inactivated influenza vaccines is determined using a single radial immunodiffusion (SRID) assay. This assay is relatively easy to standardize, it is not technically demanding, and it is capable of measuring the potency of several vaccine strain subtypes in a multivalent vaccine. Nevertheless, alternative methods that retain the major advantages of the SRID, but with a greater dynamic range of measurement and with reduced reagent requirements, are needed. OBJECTIVES: The feasibility of an ELISA-based assay format was explored as an alternative potency assay for inactivated influenza vaccines. METHODS: Several murine monoclonal antibodies (mAbs), specific for the 2009 pandemic H1N1 influenza virus hemagglutinin (HA), were evaluated for their potential to capture and quantify HA antigen. Vaccine samples, obtained from four licensed influenza vaccine manufacturers, included monovalent bulk vaccine, monovalent vaccine, and trivalent vaccine. Traditional SRID potency assays were run in parallel with the mAb-ELISA potency assay using the reference antigen standard appropriate for the vaccine samples being tested. RESULTS: The results indicated that the ELISA potency assay can quantify HA over a wide range of concentrations, including vaccine at subpotent doses, and the ELISA and SRID potency values correlated well for most vaccine samples. Importantly, the assay was capable of quantifying A/California HA in a trivalent formulation. CONCLUSIONS: This study demonstrates the general feasibility of the mAb approach and strongly suggests that such ELISAs have potential for continued development as an alternative method to assay the potency of inactivated influenza vaccines.

Neutralizing and protective epitopes of the 2009 pandemic influenza H1N1 hemagglutinin.

AIMS AND METHODS: To facilitate antigenic characterization of the influenza A 2009 pandemic H1N1 [A(H1N1)pdm09] hemagglutinin (HA), we generated a panel of murine monoclonal antibodies (mAbs) using as the immunogen mammalian-derived virus-like particles containing the HA of the A/California/04/2009 virus. The antibodies were specific for the A/California/04/2009 HA, and individual mAbs suitable for use in several practical applications including ELISA, immunofluorescence, and Western blot analysis were identified. RESULTS AND CONCLUSIONS: As the panel of mAbs included antibodies with hemagglutination inhibition (HI) and virus neutralizing activities, this allowed identification and characterization of potentially important antigenic and neutralizing epitopes of the A/California/04/2009 HA and comparison of those epitopes with the HAs of other influenza viruses including seasonal H1N1 viruses as well as the A/South Carolina/1918 and A/New Jersey/1976 H1N1 viruses. Three mAbs with the highest HI and neutralizing titers were able to provide passive protection against virus challenge. Two other mAbs without HI or neutralizing activities were able to provide partial protection against challenge. HA epitopes recognized by the strongest neutralizing mAbs in the panel were identified by isolation and selection of virus escape mutants in the presence of individual mAbs. Cloned viruses resistant to HI and antibody neutralization were sequenced to identify mutations, and two unique mutations (D127E and G155E) were identified, both near the antigenic site Sa. Using human post-vaccination sera, however, there were no differences in HI titer between A/California/04/2009 and either escape mutant, suggesting that these single mutations were not sufficient to abrogate a protective antibody response to the vaccine.

New neutralizing antibody epitopes in hepatitis C virus envelope glycoproteins are revealed by dissecting peptide recognition profiles.

One of the greatest challenges to HCV vaccine development is the induction of effective immune responses using recombinant proteins or vectors. In order to better understand which vaccine-induced antibodies contribute to neutralization of HCV the quality of polyclonal anti-E1E2 antibody responses in immunized mice and chimpanzees was assessed at the level of epitope recognition using peptide scanning and neutralization of chimeric 1a/2a, 1b/2a and 2a HCVcc after blocking or affinity elution of specific antibodies. Mice and chimpanzees were immunized with genotype 1a (H77) HCV gpE1E2; all samples contained cross-neutralizing antibody against HCVcc. By functionally dissecting the polyclonal immune responses we identified three new regions important for neutralization within E1 (aa264-318) and E2 (aa448-483 and aa496-515) of the HCV glycoproteins, the third of which (aa496-515) is highly conserved (85-95%) amongst genotypes. Antibodies to aa496-515 were isolated by affinity binding and elution from the serum of a vaccinated chimpanzee and found to specifically neutralize chimeric 1a/2a, 1b/2a and 2a HCVcc. IC50 titres (IgG ng/mL) for the aa496-515 eluate were calculated as 142.1, 239.37 and 487.62 against 1a/2a, 1b/2a and 2a HCVcc, respectively. Further analysis demonstrated that although antibody to this new, conserved neutralization epitope is efficiently induced with recombinant proteins in mice and chimpanzees; it is poorly induced during natural infection in patients and chimpanzees (7 out of 68 samples positive) suggesting the epitope is poorly presented to the immune system in the context of the viral particle. These findings have important implications for the development of HCV vaccines and strategies designed to protect against heterologous viruses. The data also suggest that recombinant or synthetic antigens may be more efficient at inducing neutralizing antibodies to certain epitopes and that screening virally infected patients may not be the best approach for finding new cross-reactive epitopes.

Microarray assay for evaluation of the genetic stability of modified vaccinia virus Ankara B5R gene.

Adverse events associated with the use of live smallpox vaccines have led to the development of a new generation of attenuated smallpox vaccines that are prepared in cultured cells as alternatives. The inability to conduct direct clinical evaluation of their efficacy in humans demands that licensure be based on animal studies and exhaustive evaluation of their in vitro properties. One of the most important characteristics of live viral vaccines is their genetic stability, including reversion of the vaccine strain to more virulent forms, recombination with other viral sequences to produce potentially pathogenic viruses, and genetic drift that can result in decrease of immunogenicity and efficacy. To study genetic stability of an immunoessential vaccinia virus gene in a new generation smallpox vaccine, an advanced oligonucleotide microchip was developed and used to assay for mutations that could emerge in B5R gene, a vaccinia virus gene encoding for a protein that contains very important neutralizing epitopes. This microarray contained overlapping oligonucleotides covering the B5R gene of modified vaccinia virus Ankara (MVA), a well-studied candidate smallpox vaccine. The microarray assay was shown to be able to detect even a single point mutation, and to differentiate between vaccinia strains. At the same time, it could detect newly emerged mutations in clones of vaccinia strains. In the work described here, it was shown that MVA B5R gene was stable after 34 passages in Vero and MRC-5 cells that were proposed for use as cell substrates for vaccine manufacture. Potentially, the proposed method could be used as an identity test and could be extended for the entire viral genome and used to monitor consistency of vaccine production.

CD4+ immune escape and subsequent T-cell failure following chimpanzee immunization against hepatitis C virus.

Hepatitis C is a major cause of chronic liver disease, with 170 million individuals infected worldwide and no available vaccine. We analyzed the effects of an induced T-cell response in 3 chimpanzees, targeting nonstructural proteins in the absence of neutralizing antibodies. In all animals the specific T-cell response modified the outcome of infection, producing a 10- to 1,000-fold reduction in peak virus titers. The challenge of 2 immunized animals that had been previously exposed to hepatitis C virus resulted in subclinical infections. Immune responses in the third animal, naive prior to immunization, limited viral replication immediately, evidenced by a 30-fold reduction in virus titer by week 2, declining to a nonquantifiable level by week 6. After 10 weeks of immunological control, we observed a resurgence of virus, followed by progression to a persistent infection. Comparing virus evolution with T-cell recognition, we demonstrated that: (i) resurgence was concomitant with the emergence of new dominant viral populations bearing single amino acid changes in the NS3 and NS5A regions, (ii) these mutations resulted in a loss of CD4+ T-cell recognition, and (iii) subsequent to viral resurgence and immune escape a large fraction of NS3-specific T cells became impaired in their ability to secrete IFN-gamma and proliferate. In contrast, NS3-specific responses were sustained in the recovered/immunized animals presenting with subclinical infections. In conclusion, viral escape from CD4+ T cells can result in the eventual failure of an induced T-cell response that initially controls infection. Vaccines that can induce strong T-cell responses prior to challenge will not necessarily prevent persistent HCV infection.

Vaccinia virus nicking-joining enzyme is encoded by K4L (VACWR035).

Vaccinia virus encodes an enzyme with DNA modifying activity that cleaves and inefficiently cross-links cruciformic DNA. This enzyme is contained within the virion, expressed at late times postinfection, and processes DNA in an energy-independent, Mg2+ ion-independent manner. Viral nuclease activity was measured in extracts from cells infected with well-defined viral mutants. Since some viral extracts lacked nuclease activity, the gene encoding the activity was postulated to be one of the open reading frames absent in the viruses lacking activity. Inducible expression of each candidate open reading frame revealed that only the gene VACWR035, or K4L, was required for nuclease activity. A recombinant virus missing only the open reading frame for K4L lacked nuclease activity. Extracts from a recombinant virus expressing K4L linked to a FLAG polypeptide were able to cleave and cross-link cruciformic DNA. There were no significant differences between the virus lacking K4L and wild-type vaccinia virus WR with respect to infectivity, growth characteristics, or processing of viral replicative intermediate DNA, including both telomeric and cross-linked forms. Purification of the K4L FLAG polypeptide expressed in bacteria yielded protein containing nicking-joining activity, implying that K4L is the only vaccinia virus protein required for the nicking-joining enzymatic activity.