B. anthracis:passive immunization with anticapsular mAb

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DESCRIPTION (provided by applicant): Bacillus anthracis is surrounded by an antiphagocytic capsule that is composed of poly-gamma-D-glutamic acid (PGA). Despite an essential role for the capsule in the pathogenesis of anthrax, the immune response to the capsule has received little attention, and the protective role of PGA antibody is unknown. The overall hypothesis for this proposal is that PGA antibodies are protective against anthrax. The goal for the study is to generate a library of PGA monoclonal antibodies (mAbs) and to evaluate the properties of the antibodies in vitro and in vivo. In preliminary studies, a strong isotype-switched (IgG) and affinity-matured antibody response has been generated in mice through immunization with PGA in combination with a potent and novel B-cell adjuvant. Five hybridomas that secrete anti-PGA IgG have been generated in a very short time, and production of additional mAbs having distinct epitope specificities is in progress. Thus, the feasibility for generation of a robust antibody response in mice and for production of lgG mAbs has been demonstrated. The specific aims of the proposal are to i) generate a library of PGA IgG mAbs that represent a spectrum of epitope specificities, ii) evaluate the immunochemistry of mAb binding to soluble and capsular PGA, iii) generate IgG subclass switch variants of PGA mAbs, iv) assess in vitro activities of PGA mAbs that may be predictive of protection, and v) evaluate the role of epitope specificity and antibody isotype in determining protection in murine models of cutaneous and inhalation anthrax. Targeting the capsule for vaccine development or immunotherapy is attractive because anticapsularimmunity would not be compromised by antibiotic resistance or engineering of an anthrax toxin that is resistant to toxin-based immunity. The proposed determination of protective efficacy is central to any effort at active or passive immunization that targets the B. anthracis capsule and would provide proof of concept for passive immunization as a pre- or post-exposure immunotherapy for anthrax.