Human monoclonal antibodies generated following vaccination with AVA provide neutralization by blocking furin cleavage but not by preventing oligomerization

Generation and Characterization of Human Monoclonal Antibodies Targeting Anthrax Protective Antigen following Vaccination with a Recombinant Protective Antigen Vaccine

“…Despite the fact 8A7 that bound to the PA63 oligomers, it did not inhibit PA-mediated cellular toxicity. Interestingly, MAbs specific to PA domain 3 derived from animals or humans generally do not provide any protection against LeTx in vivo (10,14). Together with our findings, these results suggest that while MAbs specific for domain 3 of PA are not neutralizing when used alone, they may provide some benefit to the host in combination with other MAbs.…”

“…We were able to identify the specificities, function, and Ig composition of the endogenous antibody repertoire by using single-cell PCR to preserve the natural Ig VH and VL pairing from individual B cells. Despite the fact that we have characterized the response of only a single subject, the specificities and functions of the PA response in humans may be more important than the quantity of the anti-PA (10). Of the clones we isolated from the donor, 6.4% were PA reactive, and approximately one quarter of the IgG ϩ ASCs was PA reactive 7 days after the donor received a boost vaccination.…”

“…Vaccination with rPA is known to elicit a polyclonal antibody (Ab) response. Most of the studies that have been conducted characterize the antibody responses induced by the AVA vaccine in humans (10). To date, there have not been very many studies to characterize the human antibody responses to the rPA vaccine.…”

Characterization of the Native Form of Anthrax Lethal Factor for Use in the Toxin Neutralization Assay

“…The rPA component was the determining factor of neutralizing potencies of all test sera because those samples contained either anti-PA antibodies only (i.e., from rPA plus Alhydrogel vaccination) or substantially greater anti-PA neutralizing content relative to that of anti-LF that is expected in sera derived from AVA vaccinations with or without CPG 7909 (11,12). Indeed, most anthrax vaccines in development are designed to induce a strong neutralizing anti-PA antibody titer as the predominant protective mechanism (11)(12)(13)(14), in which case the rPA concentration, rather than the rLF concentration, would be the dominant component in those respective TNAs. However, the rLF concentration would be the dominant or determining component in the TNA if the anti-LF antibody neutralization titer was represented either in a pure form or in excess of anti-PA, as with a sample containing a therapeutic anti-LF monoclonal antibody (31,32) or that derived from an rLF-based vaccine.…”

“…Serum titers of anthrax LT-neutralizing antibodies following vaccination have been evaluated in animal models of anthrax disease and in human clinical immunogenicity studies (7)(8)(9)(10). While antibodies to all toxin components can be detected via an enzymelinked immunosorbent assay (ELISA) after vaccination with AVA, serum titers of antibodies to PA are most prevalent and appear to be responsible mainly for LT-neutralizing activity in the anthrax toxin neutralization assay (TNA) (11)(12)(13)(14). In fact, most reported TNAs were designed to emphasize this anti-PA antibody neutralizing contribution, which is the best-accepted correlate of immune protection for certain anthrax vaccine formulations (15)(16)(17).…”