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Each year, up to one fifth of the United States population is infected with influenza virus. Although mortality rates are low, hundreds of thousands are hospitalized each year in the United States. Specific high risk groups, such as those with suppressed or dysregulated immune systems, are at greater danger for influenza complications. Respiratory infections are a common cause of hospitalizations and early mortality in patients with systemic lupus erythematosus (SLE); however, whether this increased infection risk is a consequence of the underlying dysregulated immune background and/or immunosuppressing drugs is unknown. To evaluate the influenza immune response in the context of lupus, as well as assess the effect of infection on autoimmune disease in a controlled setting, we infected lupus-prone MRL/MpJ-Fas(lpr) mice with influenza virus A PR/8/34 H1N1. Interestingly, we found that Fas(lpr) mice generated more influenza A virus specific T cells with less neutrophil accumulation in the lung during acute infection. Moreover, Fas(lpr) mice produced fewer flu-specific IgG and IgM antibodies, but effectively cleared the virus. Further, increased extrinsic apoptosis during influenza infection led to a delay in autoimmune disease pathology with decreased severity of splenomegaly and kidney disease. Following primary influenza A infection, Fas(lpr) mice had severe complications during the contraction and resolution phase with widespread severe pulmonary inflammation. Our findings suggest that influenza infection may not exacerbate autoimmune pathology in mice during acute infection as a direct result of virus induced apoptosis. Additionally, autoimmunity drives an enhanced antigen-specific T cell response to clear the virus, but persisting pulmonary inflammation following viral clearance may cause complications in this lupus animal model.

Roughly half of U.S. adults do not receive recommended booster vaccinations, but protective antibody levels are rarely measured in adults. Demographic factors, vaccination history, and responses to other vaccinations could help identify at-risk individuals. We sought to characterize rates of seroconversion and determine associations of humoral responses to multiple vaccinations in healthy adults.Humoral responses toward measles, mumps, tetanus toxoid, pertussis, hepatitis B surface antigen, and anthrax protective antigen were measured by ELISA in post-immunization samples from 1465 healthy U.S. military members. We examined the effects of demographic and clinical factors on immunization responses, as well as assessed correlations between vaccination responses.Subsets of boosted adults did not have seroprotective levels of antibodies toward measles (10.4%), mumps (9.4%), pertussis (4.7%), hepatitis B (8.6%) or protective antigen (14.4%) detected. Half-lives of antibody responses were generally long (30 years). Measles and mumps antibody levels were correlated (r=0.31, p0.001), but not associated with select demographic features or vaccination history. Measles and mumps antibody levels also correlated with tetanus antibody response (r=0.11, p0.001).Vaccination responses are predominantly robust and vaccine specific. However, a small but significant portion of the vaccinated adult population may not have quantitative seroprotective antibody to common vaccine-preventable infections.

In order to identify the combination of antibody-mediated mechanisms of neutralization that result from vaccination with anthrax vaccine adsorbed (AVA), we isolated antibody secreting cells from a single donor seven days after booster vaccination with AVA and generated nine fully human monoclonal antibodies (hmAb) with high specificity for protective antigen (PA). Two of the antibodies were able to neutralize lethal toxin in vitro at low concentrations (IC(50): p6C01, 0.12 μg/ml and p6F01, 0.45 μg/ml). Passive transfer of either of these hmAbs to A/J mice prior to challenge with lethal toxin conferred 80-90% protection. We demonstrate that hmAb p6C01 is neutralizing by preventing furin cleavage of PA in a dose-dependent manner, but the mechanism of p6F01 is unclear. Three additional antibodies were found to bind to domain 3 of PA and prevent oligomerization, although they did not confer significant protection in vivo and showed a significant prozone-like effect in vitro. These fully human antibodies provide insight into the neutralizing response to AVA for future subunit vaccine and passive immunotherapeutic cocktail design.

Background: Antiphospholipid syndrome is characterized by autoantibodies against cardiolipins (aCL), lupus anticoagulant, and independent β2-glycoprotein (β2GPI). Controversy exists as to whether vaccination triggers the development of antiphospholipid antibodies (aPL) in patients with systemic lupus erythematosus (SLE). Methods: Patients with SLE (101) and matched controls (101) were enrolled from 2005–2009 and received seasonal influenza vaccinations. Sera were tested by ELISA for aCL at baseline, 2, 6, and 12 weeks after vaccination. Vaccine responses were ranked according to an overall anti-influenza antibody response index. Individuals with positive aCL were further tested for β2GPI antibodies. Results: Patients with SLE and healthy controls can develop new-onset aCL post vaccination, although at rates which do not differ between patients and controls (12/101 cases and 7/101 controls, OR 1.81, p = 0.34). New-onset moderate aCL are slightly enriched in African American SLE patients (5/36 cases; p = 0.094). The optical density measurements for aCL reactivity in patients were significantly higher than baseline at 2 weeks ( p Conclusions: This study shows transient increases in aCL, but not anti-β2GPI responses, after influenza vaccination.

Vitamin D deficiency is widespread and has been associated with many chronic diseases, including autoimmune disorders. A study was undertaken to explore the impact of low vitamin D levels on autoantibody production in healthy individuals, as well as B cell hyperactivity and interferon α (IFNα) activity in patients with systemic lupus erythematosus (SLE).Serum samples from 32 European American female patients with SLE and 32 matched controls were tested for 25-hydroxyvitamin D (25(OH)D) levels, lupus-associated autoantibodies and serum IFNα activity. Isolated peripheral blood mononuclear cells were tested for intracellular phospho-ERK 1/2 as a measure of B cell activation status.Vitamin D deficiency (25(OH)D20 ng/ml) was significantly more frequent among patients with SLE (n=32, 69%) and antinuclear antibody (ANA)-positive controls (n=14, 71%) compared with ANA-negative controls (n=18, 22%) (OR 7.7, 95% CI 2.0 to 29.4, p=0.003 and OR 8.8, 95% CI 1.8 to 43.6, p=0.011, respectively). Patients with high B cell activation had lower mean (SD) 25(OH)D levels than patients with low B cell activation (17.2 (5.1) vs 24.2 (3.9) ng/ml; p=0.009). Patients with vitamin D deficiency also had higher mean (SD) serum IFNα activity than patients without vitamin D deficiency (3.5 (6.6) vs 0.3 (0.3); p=0.02).The observation that ANA-positive healthy controls are significantly more likely to be deficient in vitamin D than ANA-negative healthy controls, together with the finding that vitamin D deficiency is associated with certain immune abnormalities in SLE, suggests that vitamin D plays an important role in autoantibody production and SLE pathogenesis.

The bipartite anthrax lethal toxin (LeTx) consisting of protective antigen (PA) and lethal factor (LF) is a major virulence factor contributing to death from systemicBacillus anthracisinfection. The current vaccine elicits antibodies directed primarily to PA; however, in experimental settings serologic responses to LF can neutralize LeTx and contribute to protection against infection. The goals of the present study were to identify sequential B-cell epitopes of LF and to determine the capacity of these determinants to bind neutralizing antibodies. Sera of recombinant LF-immunized A/J mice exhibited high titers of immunoglobulin G anti-LF reactivity that neutralized LeTx in vitro 78 days after the final booster immunization and protected the mice from in vivo challenge with 3 50% lethal doses of LeTx. These sera bound multiple discontinuous epitopes, and there were major clusters of reactivity on native LF. Strikingly, all three neutralizing, LF-specific monoclonal antibodies tested bound specific peptide sequences that coincided with sequential epitopes identified in polyclonal antisera from recombinant LF-immunized mice. This study confirms that LF induces high-titer protective antibodies in vitro and in vivo. Moreover, the binding of short LF peptides by LF-specific neutralizing monoclonal antibodies suggests that generation of protective antibodies by peptide vaccination may be feasible for this antigen. This study paves the way for a more effective anthrax vaccine by identifying discontinuous peptide epitopes of LF.

The identification of T cell epitopes is crucial for the understanding of the host immune response during infection. While much is known about the MHC class I-restricted response following influenza virus infection of C57BL/6 mice, with over 16 CD8 epitopes identified to date, less is known about the MHC class II-restricted response. Currently, only a few I-A(b)-restricted T helper epitopes have been identified. Therefore, several important questions remain about how many class II epitopes exist in this system and whether these epitopes are evenly distributed within the most abundant viral proteins. In order to address these questions, we analyzed the repertoire of epitopes that drive the CD4+ approximately 20-30 epitopes drive the CD4 T cell response and that the majority of these peptides are derived from the NP and HA proteins. We were also able to demonstrate that vaccination with one of the newly identified epitopes, HA(211-225)/A(b), resulted in increased epitope-specific T cell numbers and a significant reduction in viral titers following influenza virus challenge.

The mechanisms underlying epitope selection and the potential impact of immunodominance hierarchies on peptide-based vaccines are not well understood. Recently, we have shown that two immunodominant MHC class I-restricted epitopes, NP366–374/Db (nucleoprotein (NP)) and PA224–233/Db (acidic polymerase (PA)), which drive the CD8+ T cell response to influenza virus infection in C57BL/6 mice, are differentially expressed on infected cells. Whereas NP appears to be strongly expressed on all infected cells, PA appears to be strongly expressed on dendritic cells but only weakly expressed on nondendritic cells. Thus, the immune response to influenza virus may involve T cells specific for epitopes, such as PA, that are poorly expressed at the site of infection. To examine the consequences of differential Ag presentation on peptide vaccination, we compared the kinetics of the T cell response and influenza virus clearance in mice vaccinated with the NP or PA peptide. Vaccination with either the NP or PA peptide resulted in accelerated and enhanced Ag-specific T cell responses at the site of infection following influenza virus challenge. These T cells were fully functional in terms of their ability to produce IFN-γ and TNF-α and to mediate cytolytic activity. Despite this enhancement of the Ag-specific T cell response, PA vaccination had a detrimental effect on the clearance of influenza virus compared with unvaccinated or NP-vaccinated mice. These data suggest that differential Ag presentation impacts the efficacy of T cell responses to specific epitopes and that this needs to be considered for the development of peptide-based vaccination strategies.

The development of vaccines designed to promote cellular immunity to pulmonary virus infections continues to be a significant problem for vaccinologists. This is primarily due to our poor understanding of the mechanisms underlying the establishment and recall of T cell memory at mucosal surfaces such as the lung airways. Recent studies in the mouse have revealed that memory CD8+ T cell populations are extremely heterogeneous in terms of phenotype, function, anatomical distribution, and longevity and that different subpopulations play distinct roles in the recall response. Moreover, our recent data suggest that the recall response is comprised of temporally distinct phases that involve different subpopulations of memory T cells. Current studies are directed at understanding which memory T cell subsets are elicited by different vaccination strategies and to determine how this impacts the efficacy of the vaccine against secondary virus challenge.

The specificity of CD8+ T cell responses can vary dramatically between primary and secondary infections. For example, NP366–374/Db- and PA224–233/Db-specific CD8+ T cells respond in approximately equal numbers to a primary influenza virus infection in C57BL/6 mice, whereas NP366–374/Db-specific CD8+ T cells dominate the secondary response. To investigate the mechanisms underlying this changing pattern of immunodominance, we analyzed the role of antigen presentation in regulating the specificity of the T cell response. The data show that both dendritic and nondendritic cells are able to present the NP366–374/Db epitope, whereas only dendritic cells effectively present the PA224–233/Db epitope after influenza virus infection, both in vitro and in vivo. This difference in epitope expression favored the activation and expansion of NP366–374/Db-specific CD8+ memory T cells during secondary infection. The data also show that the immune response to influenza virus infection may involve T cells specific for epitopes, such as PA224–233/Db, that are poorly expressed at the site of infection. In this regard, vaccination with the PA224–233 peptide actually had a detrimental effect on the clearance of a subsequent influenza virus infection. Thus, differential antigen presentation impacts both the specificity of the T cell response and the efficacy of peptide-based vaccination strategies.

Kinetic studies and short pulses of injected 5-bromo-2-deoxyuridine have been used to analyze the development and renewal of peripheral CD8+ memory T cells in the lungs during primary and secondary respiratory virus infections. We show that developing peripheral CD8+ memory T cells proliferate during acute viral infection with kinetics that are indistinguishable from those of lymphoid CD8+ memory T cells. Secondary exposure to the same virus induces a new round of T cell proliferation and extensive renewal of the peripheral and lymphoid CD8+ memory T cell pools in both B cell-deficient mice and mice with immune Abs. In mice with virus-specific Abs, CD8+ T cell proliferation takes place with minimal inflammation or effector cell recruitment to the lungs. The delayed arrival of CD8+ memory T cells to the lungs of these animals suggests that developing memory cells do not require the same inflammatory signals as effector cells to reach the lung airways. These studies provide important new insight into mechanisms that control the maintenance and renewal of peripheral memory T cell populations during natural infections.

There has been an increasing interest in developing vaccines which are both easy to administer and which elicit functionally protective immune responses at mucosal and/or systemic sites. Intranasally administered vaccines meet the criteria of ease of administration and are thought to stimulate respiratory-mucosal immunity via interaction with nasal associated lymphoid tissues (NALT). The aim of this study was to gain a better understanding of how best to stimulate respiratory-mucosal immunity using a murine model of respiratory reovirus infection. Either a predominantly upper respiratory tract infection or a combination upper and lower respiratory tract infection was established by administering the same virus dose in either a small or large inoculum volume. These studies demonstrate that stimulation of NALT alone by an upper respiratory tract infection does not induce an optimal primary antibody response even in the nasal cavity. Effective immunity of both the upper and lower respiratory tract was obtained when a combination upper and lower respiratory tract infection was established. These results have important clinical implications since they suggest that effective respiratory mucosal immunity will be best achieved by the combined stimulation of both the upper and lower respiratory tract and will likely require both intranasal as well as inhaled aerosol delivery of antigen to the lower respiratory tract in humans.

Anthrax Lethal Toxin consists of Protective Antigen (PA) and Lethal Factor (LF), and current vaccination strategies focus on eliciting antibodies to PA. In human vaccination, the response to PA can vary greatly, and the response is often directed toward non-neutralizing epitopes. Variable vaccine responses have been shown to be due in part to genetic differences in individuals, with both MHC class II and other genes playing roles. Here, we investigated the relative contribution of MHC class II versus non-MHC class II genes in the humoral response to PA and LF immunization using three immunized strains of inbred mice: A/J (H-2k at the MHC class II locus), B6 (H-2b), and B6.H2k (H-2k). IgG antibody titers to LF were controlled primarily by the MHC class II locus, whereas IgG titers to PA were strongly influenced by the non-MHC class II genetic background. Conversely, the humoral fine specificity of reactivity to LF appeared to be controlled primarily through non-MHC class II genes, while the specificity of reactivity to PA was more dependent on MHC class II. Common epitopes, reactive in all strains, occurred in both LF and PA responses. These results demonstrate that MHC class II differentially influences humoral immune responses to LF and PA.

B lymphocyte stimulator (BLyS, also known as TNFSF13B and BAFF) is a type II transmembrane protein and a member of the TNF superfamily (1, 2). BLyS is produced by several different cell types, including monocytes, activated neutrophils, T cells, and dendritic cells (3–5), and is expressed as a cell surface protein which can be furin-cleaved and released into the circulation. Although BLyS has been shown to be constitutively expressed, certain inflammatory cytokines such as IL-2, TNF-α, IFN-γ, and IFN-α can enhance its production and secretion (3, 4, 6, 7). BLyS binds to 3 receptors found primarily on B cells (8). Activation of these receptors leads to B cell proliferation, differentiation, survival, and IgG class switching (1, 4, 9). BLyS has been shown to play an important role in primary immune responses, as anti-BLyS treated mice show profoundly reduced numbers of naive B cells with accompanying attenuated responses to both T-dependent and T-independent antigens (10). Transgenic mice that overexpress BLyS display a myriad of autoimmune features, such as high levels of rheumatoid factor, anti-DNA, circulating immune complexes, and immunoglobulin deposition in the kidneys (9). Mice treated with exogenous BLyS develop an increase in B cell numbers, particularly those directed against chromatin (11), and autoreactive cells encountering transitional B cell checkpoints in the spleen require higher concentrations of BLyS to survive than do non-autoreactive B cells (8, 9, 12). Mouse models have also demonstrated that deletion of either BLyS or its receptor severely impairs B cell development beyond the transitional stage with a resulting decrease in peripheral B cell populations (9, 13–15). Elevated circulating BLyS levels have been found in patients with systemic autoimmune disorders such as SLE, rheumatoid arthritis (RA), and Sjoren’s syndrome (16–18). Early reports found increased serum BLyS levels in SLE patients compared to healthy individuals that correlated with anti-dsDNA titers, but not disease activity (16, 17, 19). BLyS levels did, however, decrease following high-dose corticosteroid treatment (19). Other studies found that peripheral blood leukocyte BLyS mRNA levels correlated with SLE disease activity (20, 21). While most of these initial studies, which were performed in mainly Hispanic SLE patients, failed to demonstrate a correlation between serum BLyS levels and disease activity, a later longitudinal study undertaken at 4 different clinical centers that contained ancestral diversity, found an association between increases in plasma BLyS levels from a previous visit and increases in SELENA-SLEDAI scores at the next visit (22). Additionally, another study involving Norwegian SLE patients, also found a correlation with serum BLyS levels and SLEDAI scores (23). A study examining plasma BLyS protein levels in pediatric SLE also demonstrated an association between elevated BLyS levels and increased disease activity (24). IFN-α has proven to be a key cytokine in SLE pathogenesis, and has been shown to increase BLyS expression in antigen-presenting cells (4). Therefore, it is possible that IFN-α plays a role in driving BLyS production in SLE, although a direct correlation between circulating BLyS levels and serum IFN-α activity has yet to be demonstrated in SLE patients. Additionally, several environmental factors have been implicated in the pathogenesis of SLE (25), including vitamin D deficiency (26). As vitamin D has been shown to suppress the expression of the IFN signature in myeloid-derived dendritic cells, as well as suppress B cell activation and immunoglobulin production (27, 28), it is of interest to assess the relationship between vitamin D and BLyS levels. Belimumab is a fully human monoclonal antibody that binds BLyS and inhibits its activity. Two recent large randomized, double-blind, placebo-controlled, multicenter phase 3 trials, BLISS-52 and BLISS-76, evaluated the efficacy of belimumab plus standard of care compared to placebo plus standard of care; positive results were obtained with both studies reaching their primary efficacy endpoints of reductions in disease activity without ancillary organ flares (29, 30). Taken together, these data suggest that excessive BLyS may be an important mechanism underlying SLE pathogenesis and that BLyS targeted therapies seem promising. However, normal B cell function requires some BLyS activity. To date no studies have evaluated whether specific levels of BLyS are required to mount appropriate vaccination responses or whether BLyS levels change after vaccination. The primary objective of this study is to investigate the relationship between circulating BLyS levels and humoral responses made to influenza vaccination, as well as the effect of influenza vaccination on BLyS production in SLE. The current study also examines select demographic, environmental, and clinical features of SLE for association with elevated BLyS levels in an effort to better understand the mechanisms of elevated BLyS in a heterogeneous SLE population.

The efficacy biomarker of the currently licensed anthrax vaccine (AVA) is based on quantity and neutralizing capacity of anti-protective antigen (anti-PA) antibodies. However, animal studies have demonstrated that antibodies to lethal factor (LF) can provide protection against in vivo bacterial spore challenges. Improved understanding of the fine specificities of humoral immune responses that provide optimum neutralization capacity may enhance the efficacy of future passive immune globulin preparations to treat and prevent inhalation anthrax morbidity and mortality. This study ( n = 1000) was designed to identify AVA vaccinated individuals who generate neutralizing antibodies and to determine what specificities correlate with protection. The number of vaccine doses, years post vaccination, and PA titer were associated with in vitro neutralization, reinforcing previous reports. In addition, African American individuals had lower serologic neutralizing activity than European Americans, suggesting a genetic role in the generation of these neutralizing antibodies. Of the vaccinated individuals, only 69 (6.9%) had moderate levels of anti-LF IgG compared to 244 (24.4%) with low and 687 (68.7%) with extremely low levels of IgG antibodies to LF. Using overlapping decapeptide analysis, we identified six common LF antigenic regions targeted by those individuals with moderate levels of antibodies to LF and high in vitro toxin neutralizing activity. Affinity purified antibodies directed against antigenic epitopes within the PA binding and ADP-ribotransferase-like domains of LF were able to protect mice against lethal toxin challenge. Findings from these studies have important implications for vaccine design and immunotherapeutic development.

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 providing protection through post exposure 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 levels of in vitro toxin neutralization capacity in their sera. Using solid phase epitope mapping and confirmatory assays, we identified several neutralization-associated humoral epitopes and demonstrated that select anti-peptide 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.

The expression of IFN-γ is a hallmark of Th1 cells and CD8+ effector T cells and is the signature cytokine of type 1 responses. However, it is not known whether T cells are homogeneous in their capacity to produce IFN-γ, whether this potential varies between tissues, and how it relates to the production of other effector molecules. In the present study we used bicistronic IFN-γ-enhanced yellow fluorescent protein (IFN-γ-eYFP) reporter mice (Yeti) and MHC class I tetramers to directly quantify IFN-γ expression at the single cell level. The eYFP fluorescence of Th1 cells and CD8+ effector T cells was broadly heterogeneous even before cell division and correlated with both the abundance of IFN-γ transcripts and the secretion of IFN-γ upon stimulation. CD4+ and CD8+ T cells of influenza-infected mice revealed a similarly heterogeneous IFN-γ expression, and eYFPhigh cells were only found in the infected lung. Ag-specific T cells were in all examined tissues eYFP+, but also heterogeneous in their reporter fluorescence, and eYFPhigh cells were also restricted to the infected lung. A similar heterogeneity was observed in Toxoplasma gondii-infected animals, but eYFPhigh cells were restricted to different tissues. Highly eYFP fluorescent cells produced elevated levels of proinflammatory cytokines and chemokines in addition to IFN-γ, suggesting their coregulated expression as a functional unit in highly differentiated effector T cells.

Recent studies have identified distinct populations of memory T cells that persist in the lungs following respiratory virus infections, and contribute to the control of secondary virus infections. Here we discuss the establishment, maintenance and recall of memory T cells in the lung.

The release of Bacillus anthracis spores can cause significant morbidity and mortality and an effective vaccine as well as directed immunotherapeutics are needed. The currently licensed vaccine requires six primary vaccinations, annual boosters, and has been associated with serious adverse events. Thus there is increasing interest in developing an improved vaccination strategy which can generate lasting protective immunity with reduced vaccinations. This study seeks to identify the major humoral targets of B. anthracis that provide protection. To this end, plasma was obtained from two hundred vaccinated individuals and thirty unvaccinated controls. Ninety-five percent of all vaccinated individuals had anti-protective antigen antibodies and these antibodies correlated with in vitro protection against lethal toxin. Utilizing overlapping decapeptides, we identified common antigenic regions within those individuals with high toxin neutralizing activity. Epitope-specific antibodies directed against three of these regions were isolated and were able to mediate protection in vitro and in a mouse model of in vivo lethal toxin challenge. Identification of common, protective, peptide-specific humoral immune responses provide key information for further immunotherapeutic and vaccine development. NIAID: 5U19AI062629

The goal of this study is to understand intrinsic and extrinsic defects in influenza vaccination responses in systemic lupus erythematosus (SLE) patients. SLE is a prototypic autoimmune disease characterized by high titers of autoantibodies. We enrolled 72 patients to evaluate anti-influenza antibody responses, autoantibody titers and disease activity after vaccination. In addition, detailed clinical and demographic information was collected. Individuals received the current influenza vaccine and sera were collected at baseline, 2, 6, and 12 weeks post vaccination. Based upon post-vaccination antibody responses, relative antibody affinities and hemaglutination inhibition levels, patients were grouped into "high" and "low" responders. Surprisingly, the high responder group was enriched in older subjects and African Americans. Patients with high anti-influenza antibodies had an increased frequency of discoid rash and anti-nRNP autoantibodies, while patients with low antibody responses had an increase in hematological criteria and anti-aPL autoantibodies. Interestingly, several patients had increased autoantibody titers following vaccination, but there were no significant associated increases in disease flare. In summary, specific demographic, clinical, and autoantibody features were associated with poor antibody responses to influenza vaccination in SLE patients. NIH: NO1-AI-50026

The currently licensed anthrax vaccine (AVA) has been designed to elicit primarily an anti-protective antigen response. However, animal studies have clearly demonstrated that antibodies to the lethal factor component of the toxin can provide protection against challenge. This study was designed to identify AVA vaccinated individuals that generate anti-LF responses and to determine if these anti-LF antibodies can mediate protection. Plasma was obtained from one thousand vaccinated individuals and thirty unvaccinated controls. Only 69 individuals (6.9%) had significant levels of anti-LF antibodies. The presence of these antibodies did not correlate with in vitro protection against lethal toxin. To determine if antibodies against specific regions of LF could mediate protection, we used overlapping decapeptides to identify six common antigenic regions within those individuals with high levels of anti-LF antibodies and high toxin neutralizing activity. Epitope-specific antibodies directed against three of these common antigenic regions were isolated and select antibodies were able to protect in both in vitro tissue culture and in vivo mouse toxin challenge models. Findings from these studies have important implications for vaccine design and immunotherapeutic development. NIAID: 5U19AI062629