Meade Biologics

Hillsborough, NC, United States

Meade Biologics

Hillsborough, NC, United States

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Ngundi M.M.,U.S. Food and Drug Administration | Meade B.D.,Meade Biologics | Little S.F.,U.S. Army | Quinn C.P.,Centers for Disease Control and Prevention | And 3 more authors.
Clinical and Vaccine Immunology | Year: 2012

Antibodies against the protective antigen (PA) component of anthrax toxin play an important role in protection against disease caused by Bacillus anthracis. In this study, we examined defined combinations of PA-specific monoclonal antibodies for their ability to neutralize anthrax toxin in cell culture assays. We observed additive, synergistic, and antagonistic effects of the antibodies depending on the specific antibody combination examined and the specific assay used. Synergistic toxin-neutralizing antibody interactions were examined in more detail. We found that one mechanism that can lead to antibody synergy is the bridging of PA monomers by one antibody, with resultant bivalent binding of the second antibody. These results may aid in optimal design of new vaccines and antibody therapies against anthrax. Copyright © 2012, American Society for Microbiology.


Verma A.,U.S. Food and Drug Administration | McNichol B.,U.S. Food and Drug Administration | McNichol B.,Pennsylvania State University | Dominguez-Castillo R.I.,U.S. Food and Drug Administration | And 7 more authors.
Infection and Immunity | Year: 2013

Long-term stability is a desired characteristic of vaccines, especially anthrax vaccines, which must be stockpiled forlarge-scale use in an emergency situation; however, spontaneous deamidation of purified vaccine antigens has the potential to adversely affect vaccine immunogenicity over time. In order to explore whether spontaneous deamidation of recombinant protective antigen (rPA)-the major component of new-generation anthrax vaccines-affects vaccine immunogenicity, we created a "genetically deamidated" form of rPA using site-directed mutagenesis to replace six deamidation-prone asparagine residues,at positions 408, 466, 537, 601, 713, and 719, with either aspartate, glutamine, or alanine residues. We found that the structure of the six-Asp mutant rPA was not significantly altered relative to that of the wild-type protein as assessed by circular dichroism (CD) spectroscopy and biological activity. In contrast, immunogenicity of aluminum-adjuvanted six-Asp mutantrPA, as measured by induction of toxin-neutralizing antibodies, was significantly lower than that of the corresponding wild-type rPA vaccine formulation. The six-Gln and six-Ala mutants also exhibited lower immunogenicity than the wild type. While the wild-type rPA vaccine formulation exhibited a high level of immunogenicity initially, its immunogenicity declined significantly upon storage at 25°C for 4 weeks. In contrast, the immunogenicity of the six-Asp mutant rPA vaccine formulation was low initially but did not change significantly upon storage. Taken together, results from this study suggest that spontaneous deamidation of asparagine residues predicted to occur during storage of rPA vaccines would adversely affect vaccine immunogenicity and therefore the storage life of vaccines. © 2013, American Society for Microbiology.


Wagner L.,U.S. Food and Drug Administration | Verma A.,U.S. Food and Drug Administration | Meade B.D.,Meade Biologics | Reiter K.,National Institute of Allergy and Infectious Diseases | And 4 more authors.
Clinical and Vaccine Immunology | Year: 2012

New anthrax vaccines currently under development are based on recombinant protective antigen (rPA) and formulated with aluminum adjuvant. Because long-term stability is a desired characteristic of these vaccines, an understanding of the effects of adsorption to aluminum adjuvants on the structure of rPA is important. Using both biophysical and immunological techniques, we compared the structure and immunogenicity of freshly prepared rPA-Alhydrogel formulations to that of formulations stored for 3 weeks at either room temperature or 37°C in order to assess the changes in rPA structure that might occur upon long-term storage on aluminum adjuvant. Intrinsic fluorescence emission spectra of tryptophan residues indicated that some tertiary structure alterations of rPA occurred during storage on Alhydrogel. Using anti-PA monoclonal antibodies to probe specific regions of the adsorbed rPA molecule, we found that two monoclonal antibodies that recognize epitopes located in domain 1 of PA exhibited greater reactivity to the stored formulations than to freshly prepared formulations. Immunogenicity of rPA-Alhydrogel formulations in mice was assessed by measuring the induction of toxin-neutralizing antibodies, as well as antibodies reactive to 12-mer peptides spanning the length of PA. Mice immunized with freshly prepared formulations developed significantly higher toxin-neutralizing antibody titers than mice immunized with the stored preparations. In contrast, sera from mice immunized with stored preparations exhibited increased reactivity to nine 12-mer peptides corresponding to sequences located throughout the rPA molecule. These results demonstrate that storage of rPA-Alhydrogel formulations can lead to structural alteration of the protein and loss of the ability to elicit toxin-neutralizing antibodies. Copyright © 2012, American Society for Microbiology. All Rights Reserved.


Ngundi M.M.,CBER | Meade B.D.,Meade Biologics | Lin T.-L.,CBER | Tang W.-J.,University of Chicago | Burns D.L.,CBER
Clinical and Vaccine Immunology | Year: 2010

Different types of anthrax toxin neutralization assays have been utilized to measure the antibody levels elicited by anthrax vaccines in both nonclinical and clinical studies. In the present study, we sought to determine whether three commonly used toxin neutralization assays - J774A.1 cell-, RAW 264.7 cell-, and CHO cell-based assays-yield comparable estimates of neutralization activities for sera obtained after vaccination with anthrax vaccines composed of recombinant protective antigen (rPA). In order to compare the assays, sera were assayed alongside a common reference serum sample and the neutralization titers were expressed relative to the titer for the reference sample in each assay. Analysis of sera from rabbits immunized with multiple doses of the rPA vaccine showed that for later bleeds, the quantitative agreement between the assays was good; however, for early bleeds, some heterogeneity in relative neutralization estimates was observed. Analysis of serum samples from rabbits, nonhuman primates, and humans immunized with the rPA vaccine showed that the relative neutralization estimates obtained in the different assays agreed to various extents, depending on the species of origin of the sera examined. We identified differences in the magnitudes of the Fc receptor-mediated neutralization associated with the J774A.1 cell- and RAW 264.7 cell-based assays, which may account for some of the species dependence of the assays. The differences in the relative neutralization estimates among the assays were relatively small and were always less than 2.5-fold. However, because toxin neutralization assays will likely be used to establish the efficacies of new anthrax vaccines, our findings should be considered when assay outputs are interpreted. Copyright © 2010, American Society for Microbiology. All Rights Reserved.


Brady R.A.,CBER | Verma A.,CBER | Meade B.D.,Meade Biologics | Burns D.L.,CBER
Clinical and Vaccine Immunology | Year: 2010

The licensed anthrax vaccine and many of the new anthrax vaccines being developed are based on protective antigen (PA), a nontoxic component of anthrax toxin. For this reason, an understanding of the immune response to PA vaccination is important. In this study, we examined the antibody response elicited by PA-based vaccines and identified the domains of PA that contribute to that response in humans as well as nonhuman primates (NHPs) and rabbits, animal species that will be used to generate efficacy data to support approval of new anthrax vaccines. To this end, we developed a competitive enzyme-linked immunosorbent assay (ELISA), using purified recombinant forms of intact PA and its individual domains. We found that PA-based vaccines elicited IgG antibodies to each of the four PA domains in all three species. We also developed a competitive toxin neutralization assay, which showed that rabbits, NHPs, and humans all have functional antibody populations that bind to domains 1, 3, and 4. While the domain specificities of the antibody responses elicited by PA-based vaccines were similar in humans, NHPs, and rabbits, competitive assays suggested that humans may have a more significant secondary population of IgG antibodies that bind to partially unfolded or incorrectly folded PA. These findings provide information that will be useful when linking animal protection data to humans via an antibody bridge to establish efficacy of new anthrax vaccines. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

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