Select Human Anthrax Protective Antigen Epitope-Specific Antibodies Provide Protection from Lethal Toxin Challenge

Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, USA.
The Journal of Infectious Diseases (Impact Factor: 6). 07/2010; 202(2):251-60. DOI: 10.1086/653495
Source: PubMed


Bacillus anthracis remains a serious bioterrorism concern, and the currently licensed vaccine remains an incomplete solution for population
protection from inhalation anthrax and has been associated with concerns regarding efficacy and safety. Thus, understanding
how to generate long-lasting protective immunity with reduced immunizations or provide protection through postexposure immunotherapeutics
are long-sought goals. Through evaluation of a large military cohort, we characterized the levels of antibodies against protective
antigen and found that over half of anthrax vaccinees had low serum levels of in vitro toxin neutralization capacity. Using
solid-phase epitope mapping and confirmatory assays, we identified several neutralization-associated humoral epitopes and
demonstrated that select antipeptide responses mediated protection in vitro. Finally, passively transferred antibodies specific
for select epitopes provided protection in an in vivo lethal toxin mouse model. Identification of these antigenic regions
has important implications for vaccine design and the development of directed immunotherapeutics.

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Available from: Sherry Crowe, Jul 14, 2014
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    • "In turn, LTNA has been demonstrated to be predictive of survival in several animal models, including a non-human primate Bacillus anthracis spore challenge model [11]. However, a subset of vaccinated military personnel may not be adequately protected in the event of spore exposure [12,13]. Among individuals vaccinated three or more times with AVA and receiving their most recent vaccination within the year prior to sample collection (n = 1422), 17.6% do not have significant plasma anti-PA IgG (<10 µg/mL), and 30.9% neutralize toxin no better than unvaccinated controls (<12% viability) [12,13]. "
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    ABSTRACT: Anthrax Vaccine Adsorbed (AVA) generates short-lived protective antigen (PA) specific IgG that correlates with in vitro toxin neutralization and protection from Bacillus anthracis challenge. Animal studies suggest that when PA-specific IgG has waned, survival after spore challenge correlates with an activation of PA-specific memory B cells. Here, we characterize the quantity and the longevity of AVA-induced memory B cell responses in humans. Peripheral blood mononuclear cells (PBMCs) from individuals vaccinated ≥3 times with AVA (n = 50) were collected early (3-6 months, n = 27) or late after their last vaccination (2-5 years, n = 23), pan-stimulated, and assayed by ELISPOT for total and PA-specific memory B cells differentiated into antibody secreting cells (ASCs). PA-specific ASC percentages ranged from 0.02% to 6.25% (median: 1.57%) and did not differ between early and late post-vaccination individuals. PA-specific ASC percentages correlated with plasma PA-specific IgG (r = 0.42, p = 0.03) and toxin neutralization (r = 0.52, p = 0.003) early post vaccination. PA-specific ASC percentages correlated with supernatant anti-PA both early (r = 0.60, p = 0.001) and late post vaccination (r = 0.71, p < 0.0001). These data suggest PA-specific memory B cell responses are long-lived and can be estimated after recent vaccination by the magnitude and neutralization capacity of the humoral response.
    Full-text · Article · Aug 2014 · Toxins
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    • "Indeed, toxin neutralisation is a main factor for protection against inhalational anthrax. Recently, a group of researchers characterised the levels of antibodies against PA and found that over half of the tested anthrax vaccines elicited responses, whereas serum samples exhibited low levels of toxin neutralisation in vitro [12]. Therefore, current evidence suggests that PA neutralisation alone does not confer optimal protection against anthrax [9]. "
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    ABSTRACT: Bacillus anthracis is the causative agent of anthrax, a bacterial infection with a high mortality rate [1-3]. Although anthrax infection can be cutaneous, gastrointestinal or pulmonary, the pulmonary form is the most deadly [2,3]. Thus, the release of Bacillus anthracis spores that can be inhaled represents a potent bioterrorism threat; the capacity of B. anthracis spores to act as a bioterrorism weapon was demonstrated in 2001, with the intentional infection of 22 persons in the U.S.A. [2,4]. Until recently, the available vaccines were developed to confer protection against cutaneous infection; despite this, these vaccines demonstrated experimental efficacy against pulmonary infection in multiple animal models [1,2]. Nevertheless, there are many limitations for these vaccines to be considered successful and effective vaccine, including the intensity of the required vaccination schedule, the administration route and the presence of local adverse effects experienced after vaccination [1,3,5,6]. To develop more efficient vaccines against pulmonary anthrax, intranasal formulations with adjuvant have been studied. These formulations have advantages because they are easy to administer and because they are expected to induce both systemic and respiratory tract mucosal immune responses. Therefore, the main goal of this review is to compare the different experimental adjuvants used with anthrax antigens and the different approaches regarding the vaccination schedule and consecutive boosters.
    Full-text · Article · Aug 2011 · World Journal of Vaccines
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    ABSTRACT: Host genetic variation, particularly within the human leukocyte antigen (HLA) loci, reportedly mediates heterogeneity in immune response to certain vaccines; however, no large study of genetic determinants of anthrax vaccine response has been described. We searched for associations between the immunoglobulin G antibody to protective antigen (AbPA) response to Anthrax Vaccine Adsorbed (AVA) in humans, and polymorphisms at HLA class I (HLA-A, -B, and -C) and class II (HLA-DRB1, -DQA1, -DQB1, -DPB1) loci. The study included 794 European-Americans and 200 African-Americans participating in a 43-month, double-blind and placebo-controlled clinical trial of AVA ( identifier NCT00119067). Among European-Americans, genes from tightly linked HLA-DRB1, -DQA1, -DQB1 haplotypes displayed significant overall associations with longitudinal variation in AbPA levels at 4, 8, 26 and 30 weeks from baseline in response to vaccination with three or four doses of AVA (global P=6.53 × 10(-4)). In particular, carriage of the DRB1-DQA1-DQB1 haplotypes (*)1501-(*)0102-(*)0602 (P=1.17 × 10(-5)), (*)0101-(*)0101-(*)0501 (P=0.009) and (*)0102-(*)0101-(*)0501 (P=0.006) was associated with significantly lower AbPA levels. In carriers of two copies of these haplotypes, lower AbPA levels persisted following subsequent vaccinations. No significant associations were observed amongst African-Americans or for any HLA class I allele/haplotype. Further studies will be required to replicate these findings and to explore the role of host genetic variation outside of the HLA region.
    Full-text · Article · Mar 2011 · Genes and immunity
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