Incomplete protection of hamsters vaccinated with unlipidated OspA from Borrelia burgdorferi infection is associated with low levels of antibody to an epitope defined by mAb LA-2

A portable immunosensor provides sensitive and rapid detection of Borrelia burgdorferi antigen in spiked blood

There are no assays for detecting B. burgdorferi antigen in blood of infected Lyme disease individuals. Here, we provide proof-of-principle evidence that we can quantify B. burgdorferi antigen in spiked blood using a portable smartphone-based fluorescence microscope that measures immunoagglutination on a paper microfluidic chip. We targeted B. burgdorferi OspA to develop a working prototype and added examples of two antigens (OspC and VlsE) that have diagnostic value for discrimination of Lyme disease stage. Using an extensively validated monoclonal antibody to OspA (LA-2), detection of OspA antigen had a broad linear range up to 100 pg/mL in 1% blood and the limit of detection (LOD) was 100 fg/mL (= 10 pg/mL in undiluted blood), which was 1000 times lower than our target of 10 ng/mL. Analysis of the two other targets was done using polyclonal and monoclonal antibodies. OspC antigen was detected at LOD 100 pg/mL (= 10 ng/mL of undiluted blood) and VlsE antigen was detected at LOD 1-10 pg/mL (= 0.1-1 ng/mL of undiluted blood). The method is accurate and was performed in 20 min from sample to answer. When optimized for detecting several B. burgdorferi antigens, this assay may differentiate active from past infections and facilitate diagnosis of Lyme disease in the initial weeks of infection, when antibody presence is typically below the threshold to be detected by serologic methods.

Engineered Bacterial Outer Membrane Vesicles with Lipidated Heterologous Antigen as an Adjuvant-Free Vaccine Platform for Streptococcus suis

Bacterial outer membrane vesicles (OMVs) are considered a promising vaccine platform for their high built-in adjuvanticity and ability to efficiently induce immune responses. OMVs can be engineered with heterologous antigens based on genetic engineering strategies. However, several critical issues should still be validated, including optimal exposure to the OMV surface, increased production of foreign antigens, nontoxicity, and induction of powerful immune protection. In this study, engineered OMVs with the lipoprotein transport machinery (Lpp) were designed to present SaoA antigen as a vaccine platform against Streptococcus suis. The results suggest that Lpp-SaoA fusions can be delivered on the OMV surface and do not have significant toxicity. Moreover, they can be engineered as lipoprotein and significantly accumulated in OMVs at high levels, thus accounting for nearly 10% of total OMV proteins. Immunization with OMVs containing Lpp-SaoA fusion antigen induced strong specific antibody responses and high levels of cytokines, as well as a balanced Th1/Th2 immune response. Furthermore, the decorated OMV vaccination significantly enhanced microbial clearance in a mouse infection model. It was found that antiserum against lipidated OMVs significantly promoted the opsonophagocytic uptake of S. suis in RAW246.7 macrophages. Lastly, OMVs engineered with Lpp-SaoA induced 100% protection against a challenge with 8× the 50% lethal dose (LD50) of S. suis serotype 2 and 80% protection against a challenge with 16× the LD50 in mice. Altogether, the results of this study provide a promising versatile strategy for the engineering of OMVs and suggest that Lpp-based OMVs may be a universal adjuvant-free vaccine platform for important pathogens. IMPORTANCE Bacterial outer membrane vesicles (OMVs) have become a promising vaccine platform due to their excellent built-in adjuvanticity properties. However, the location and amount of the expression of the heterologous antigen in the OMVs delivered by the genetic engineering strategies should be optimized. In this study, we exploited the lipoprotein transport pathway to engineer OMVs with heterologous antigen. Not only did lapidated heterologous antigen accumulate in the engineered OMV compartment at high levels, but also it was engineered to be delivered on the OMV surface, thus leading to the optimal activation of antigen-specific B cells and T cells. Immunization with engineered OMVs induced a strong antigen-specific antibodies in mice and conferred 100% protection against S. suis challenge. In general, the data of this study provide a versatile strategy for the engineering of OMVs and suggest that OMVs engineered with lipidated heterologous antigens may be a vaccine platform for significant pathogens.

Human B Cell Epitope Map of the Lyme Disease Vaccine Antigen, OspA

The Lyme disease (LD) vaccine formerly approved for use in the United States consisted of recombinant outer surface protein A (OspA) from Borrelia burgdorferi sensu stricto (ss), the bacterial genospecies responsible for the vast majority of LD in North America. OspA is an ∼30 kDa lipoprotein made up of 21 antiparallel β-strands and a C-terminal α-helix. In clinical trials, protection against LD following vaccination correlated with serum antibody titers against a single epitope near the C-terminus of OspA, as defined by the mouse monoclonal antibody (MAb), LA-2. However, the breadth of the human antibody response to OspA following vaccination remains undefined even as next-generation multivalent OspA-based vaccines are under development. In this report, we employed hydrogen exchange-mass spectrometry (HX-MS) to localize the epitopes recognized by a unique panel of OspA human MAbs, including four shown to passively protect mice against experimental B. burgdorferi infection and one isolated from a patient with antibiotic refractory Lyme arthritis. The epitopes grouped into three spatially distinct bins that, together, encompass more than half the surface-exposed area of OspA. The bins corresponded to OspA β-strands 8-10 (bin 1), 11-13 (bin 2), and 16-20 plus the C-terminal α-helix (bin 3). Bin 3 was further divided into sub-bins relative to LA-2's epitope. MAbs with complement-dependent borreliacidal activity, as well as B. burgdorferi transmission-blocking activity in the mouse model were found within each bin. Therefore, the resulting B cell epitope map encompasses functionally important targets on OspA that likely contribute to immunity to B. burgdorferi.

Agglutination of Borreliella burgdorferi by Transmission-Blocking OspA Monoclonal Antibodies and Monovalent Fab Fragments

Lyme disease vaccines based on recombinant Outer surface protein A (OspA) elicit protective antibodies that interfere with tick-to-host transmission of the disease-causing spirochete Borreliella burgdorferi. Another hallmark of OspA antisera and certain OspA monoclonal antibodies (MAbs) is their capacity to induce B. burgdorferi agglutination in vitro, a phenomenon first reported more than 30 years ago but never studied in molecular detail. In this report, we demonstrate that transmission-blocking OspA MAbs, individually and in combination, promote dose-dependent and epitope-specific agglutination of B. burgdorferi. Agglutination occurred within minutes and persisted for hours. Spirochetes in the core of the aggregates exhibited evidence of outer membrane (OM) stress, revealed by propidium iodide uptake. The most potent agglutinator was the mouse MAb LA-2, which targets the OspA C terminus (β-strands 18 to 20). Human MAb 319-44, which also targets the OspA C terminus (β-strand 20), and 857-2, which targets the OspA central β-sheet (strands 8 to 10), were less potent agglutinators, while MAb 221-7, which targets β-strands 10 to 11, had little to no measurable agglutinating activity, even though its affinity for OspA exceeded that of LA-2. Remarkably, monovalent Fab fragments derived from LA-2, and to a lesser degree 319-44, retained the capacity to induce B. burgdorferi aggregation and OM stress, a particularly intriguing observation considering that "LA-2-like" Fabs have been shown to experimentally entrap B. burgdorferi within infected ticks and prevent transmission during feeding to a mammalian host. It is therefore tempting to speculate that B. burgdorferi aggregation triggered by OspA-specific antibodies in vitro may in fact reflect an important biological activity in vivo.

Blocking Borrelia burgdorferi transmission from infected ticks to nonhuman primates with a human monoclonal antibody

Disrupting transmission of Borrelia burgdorferi sensu lato complex (B. burgdorferi) from infected ticks to humans is one strategy to prevent the significant morbidity from Lyme disease. We have previously shown that an anti-OspA human mAb, 2217, prevents transmission of B. burgdorferi from infected ticks in animal models. Maintenance of a protective plasma concentration of a human mAb for tick season presents a significant challenge for a preexposure prophylaxis strategy. Here, we describe the optimization of mAb 2217 by amino acid substitutions (2217LS: M428L and N434S) in the Fc domain. The LS mutation led to a 2-fold increase in half-life in cynomolgus monkeys. In a rhesus macaque model, 2217LS protected animals from tick transmission of spirochetes at a dose of 3 mg/kg. Crystallographic analysis of Fab in complex with OspA revealed that 2217 bound an epitope that was highly conserved among the B. burgdorferi, B. garinii, and B. afzelii species. Unlike most vaccines that may require boosters to achieve protection, our work supports the development of 2217LS as an effective preexposure prophylaxis in Lyme-endemic regions, with a single dose at the beginning of tick season offering immediate protection that remains for the duration of exposure risk.

Protection against Borreliella burgdorferi infection mediated by a synthetically engineered DNA vaccine

Lyme disease is the most common vector-borne disease in North America. The etiological agent is the spirochete Borreliella burgdorferi, transmitted to mammalian hosts by the Ixodes tick. In recent years there has been an increase in the number of cases of Lyme disease. Currently, there is no vaccine on the market for human use. We describe the development of a novel synthetically engineered DNA vaccine, pLD1 targeting the outer-surface protein A (OspA) of Borreliella burgdorferi. Immunization of C3 H/HeN mice with pLD1 elicits robust humoral and cellular immune responses that confer complete protection against a live Borreliella burgdorferi bacterial challenge. We also assessed intradermal (ID) delivery of pLD1 in Hartley guinea pigs, demonstrating the induction of robust and durable humoral immunity that lasts at least 1 year. We provide evidence of the potency of pLD1 by showing that antibodies targeting the OspA epitopes which have been associated with protection are prominently raised in the immunized guinea pigs. The described study provides the basis for the advancement of pDL1 as a potential vaccine for Lyme disease control.

Design of a broadly reactive Lyme disease vaccine

A growing global health concern, Lyme disease has become the most common tick-borne disease in the United States and Europe. Caused by the bacterial spirochete Borrelia burgdorferi sensu lato (sl), this disease can be debilitating if not treated promptly. Because diagnosis is challenging, prevention remains a priority; however, a previously licensed vaccine is no longer available to the public. Here, we designed a six component vaccine that elicits antibody (Ab) responses against all Borrelia strains that commonly cause Lyme disease in humans. The outer surface protein A (OspA) of Borrelia was fused to a bacterial ferritin to generate self-assembling nanoparticles. OspA-ferritin nanoparticles elicited durable high titer Ab responses to the seven major serotypes in mice and non-human primates at titers higher than a previously licensed vaccine. This response was durable in rhesus macaques for more than 6 months. Vaccination with adjuvanted OspA-ferritin nanoparticles stimulated protective immunity from both B. burgdorferi and B. afzelii infection in a tick-fed murine challenge model. This multivalent Lyme vaccine offers the potential to limit the spread of Lyme disease.

Broadly Protective Multivalent OspA Vaccine against Lyme Borreliosis, Developed Based on Surface Shaping of the C-Terminal Fragment

The development of vaccines for prevention of diseases caused by pathogenic species can encounter major obstacles if high sequence diversity is observed between individual strains. Therefore, development might be restricted either to conserved antigens, which are often rare, or to multivalent vaccines, which renders the production more costly and cumbersome. In light of this complexity, we applied a structure-based surface shaping approach for the development of a Lyme borreliosis (LB) vaccine suitable for the United States and Europe. The surface of the C-terminal fragment of outer surface protein A (OspA) was divided into distinct regions, based primarily on binding sites of monoclonal antibodies (MAbs). In order to target the six clinically most relevant OspA serotypes (ST) in a single protein, exposed amino acids of the individual regions were exchanged to corresponding amino acids of a chosen OspA serotype. Six chimeric proteins were constructed, and, based on their immunogenicity, four of these chimeras were tested in mouse challenge models. Significant protection could be demonstrated for all four proteins following challenge with infected ticks (OspA ST1, OspA ST2, and OspA ST4) or with in vitro-grown spirochetes (OspA ST1 and OspA ST5). Two of the chimeric proteins were linked to form a fusion protein, which provided significant protection against in vitro-grown spirochetes (OspA ST1) and infected ticks (OspA ST2). This article presents the proof-of-concept study for a multivalent OspA vaccine targeting a wide range of pathogenic LB Borrelia species with a single recombinant antigen for prevention of Lyme borreliosis.

Anti-OspA DNA-Encoded Monoclonal Antibody Prevents Transmission of Spirochetes in Tick Challenge Providing Sterilizing Immunity in Mice

We recently developed anti-OspA human immunoglobulin G1 monoclonal antibodies (HuMAbs) that are effective in preventing Borrelia transmission from ticks in a murine model. Here, we investigated a novel approach of DNA-mediated gene transfer of HuMAbs that provide protection against Lyme disease. Plasmid DNA-encoded anti-OspA HuMAbs inoculated in mice achieved a serum antibody concentration of >6 μg/mL. Among mice injected with DNA-encoded monoclonal antibodies, 75%-77% were protected against an acute challenge by Borrelia-infected ticks. Our results represent the first demonstration of employing DNA transfer as a delivery system for antibodies that block transmission of Borrelia in animal models.

Structural and molecular analysis of a protective epitope of Lyme disease antigen OspA and antibody interactions

The murine monoclonal antibody LA-2 recognizes a clinically protective epitope on outer surface protein (OspA) of Borrelia burgdorferi, the causative agent of Lyme disease in North America. Human antibody equivalence to LA-2 is the best serologic correlate of protective antibody responses following OspA vaccination. Understanding the structural and functional basis of the LA-2 protective epitope is important for developing OspA-based vaccines and discovering prophylactic antibodies against Lyme disease. Here, we present a detailed structure-based analysis of the LA-2/OspA interaction interface and identification of residues mediating antibody recognition. Mutations were introduced into both OspA and LA-2 on the basis of computational predictions on the crystal structure of the complex and experimentally tested for in vitro binding and borreliacidal activity. We find that Y32 and H49 on the LA-2 light chain, N52 on the LA-2 heavy chain and residues A208, N228 and N251 on OspA were the key constituents of OspA/LA-2 interface. These results reveal specific residues that may be exploited to modulate recognition of the protective epitope of OspA and have implications for developing prophylactic passive antibodies.

Pre-exposure Prophylaxis With OspA-Specific Human Monoclonal Antibodies Protects Mice Against Tick Transmission of Lyme Disease Spirochetes

BACKGROUND

Tick transmission of Borrelia spirochetes to humans results in significant morbidity from Lyme disease worldwide. Serum concentrations of antibodies against outer surface protein A (OspA) were shown to correlate with protection from infection with Borrelia burgdorferi, the primary cause of Lyme disease in the United States.

METHODS

Mice transgenic for human immunoglobulin genes were immunized with OspA from B. burgdorferi to generate human monoclonal antibodies (HuMabs) against OspA. HuMabs were generated and tested in in vitro borreliacidal assays and animal protection assays.

RESULTS

Nearly 100 unique OspA-specific HuMabs were generated, and 4 HuMabs (221-7, 857-2, 319-44, and 212-55) were selected as lead candidates on the basis of borreliacidal activity. HuMabs 319-44, 857-2, and 212-55 were borreliacidal against 1 or 2 Borrelia genospecies, whereas 221-7 was borreliacidal (half maximal inhibitory concentration, < 1 nM) against B. burgdorferi, Borrelia afzelii, and Borrelia garinii, the 3 main genospecies endemic in the United States, Europe, and Asia. All 4 HuMabs completely protected mice from infection at 10 mg/kg in a murine model of tick-mediated transmission of B. burgdorferi

CONCLUSIONS

Our study indicates that OspA-specific HuMabs can prevent the transmission of Borrelia and that administration of these antibodies could be employed as preexposure prophylaxis for Lyme disease.

Recombinant bacterial lipoproteins as vaccine candidates

Recombinant bacterial lipoproteins (RLP) with built-in immuno-stimulating properties for novel subunit vaccine development are reviewed. This platform technology offers the following advantages: easily converts antigens into highly immunogenic RLP using a fusion sequence containing lipobox; the lipid moiety of RLP is recognized as the danger signals in the immune system through the Toll-like receptor 2, so both innate and adaptive immune responses can be induced by RLP; serves as an efficient and cost-effective bioprocess for producing RLP in Escherichia coli and the feasibility and safety of this core platform technology has been successfully demonstrated in animal model studies including meningococcal group B subunit vaccine, dengue subunit vaccine, novel subunit vaccine against Clostridium difficile-associated diseases and HPV-based immunotherapeutic vaccines.

Recombinant Lipoproteins as Novel Vaccines with Intrinsic Adjuvant

A core platform technology for high production of recombinant lipoproteins with built-in immunostimulator for novel subunit vaccine development has been established. This platform technology has the following advantages: (1) easily convert antigen into lipidated recombinant protein using a fusion sequence containing lipobox and express high level (50-150mg/L) in Escherichia coli; (2) a robust high-yield up- and downstream bioprocess for lipoprotein production is successfully developed to devoid endotoxin contamination; (3) the lipid moiety of recombinant lipoproteins, which is identical to that of bacterial lipoproteins is recognized as danger signals by the immune system (Toll-like receptor 2 agonist), so both innate and adaptive immune responses can be induced by lipoproteins; and (4) successfully demonstrate the feasibility and safety of this core platform technology in meningococcal group B subunit vaccine, dengue subunit vaccine, novel subunit vaccine against Clostridium difficile-associated diseases, and HPV-based immunotherapeutic vaccines in animal model studies.

Design and development of a novel vaccine for protection against Lyme borreliosis

There is currently no Lyme borreliosis vaccine available for humans, although it has been shown that the disease can be prevented by immunization with an OspA-based vaccine (LYMErix). Outer surface protein A (OspA) is one of the dominant antigens expressed by the spirochetes when present in a tick. The Borrelia species causing Lyme borreliosis in Europe express different OspA serotypes on their surface, B. burgdorferi (serotype 1), B. afzelii (serotype 2), B. garinii (serotypes, 3, 5 and 6) and B. bavariensis (serotype 4), while only B. burgdorferi is present in the US. In order to target all these pathogenic Borrelia species, we have designed a multivalent OspA-based vaccine. The vaccine includes three proteins, each containing the C-terminal half of two OspA serotypes linked to form a heterodimer. In order to stabilize the C-terminal fragment and thus preserve important structural epitopes at physiological temperature, disulfide bonds were introduced. The immunogenicity was increased by introduction of a lipidation signal which ensures the addition of an N-terminal lipid moiety. Three immunizations with 3.0 µg adjuvanted vaccine protected mice from a challenge with spirochetes expressing either OspA serotype 1, 2 or 5. Mice were protected against both challenge with infected ticks and in vitro grown spirochetes. Immunological analyses (ELISA, surface binding and growth inhibition) indicated that the vaccine can provide protection against the majority of Borrelia species pathogenic for humans. This article presents the approach which allows for the generation of a hexavalent vaccine that can potentially protect against a broad range of globally distributed Borrelia species causing Lyme borreliosis.

The Cross-Talk between Spirochetal Lipoproteins and Immunity

Spirochetal diseases such as syphilis, Lyme disease, and leptospirosis are major threats to public health. However, the immunopathogenesis of these diseases has not been fully elucidated. Spirochetes interact with the host through various structural components such as lipopolysaccharides (LPS), surface lipoproteins, and glycolipids. Although spirochetal antigens such as LPS and glycolipids may contribute to the inflammatory response during spirochetal infections, spirochetes such as Treponema pallidum and Borrelia burgdorferi lack LPS. Lipoproteins are most abundant proteins that are expressed in all spirochetes and often determine how spirochetes interact with their environment. Lipoproteins are pro-inflammatory, may regulate responses from both innate and adaptive immunity and enable the spirochetes to adhere to the host or the tick midgut or to evade the immune system. However, most of the spirochetal lipoproteins have unknown function. Herein, the immunomodulatory effects of spirochetal lipoproteins are reviewed and are grouped into two main categories: effects related to immune evasion and effects related to immune activation. Understanding lipoprotein-induced immunomodulation will aid in elucidating innate immunopathogenesis processes and subsequent adaptive mechanisms potentially relevant to spirochetal disease vaccine development and to inflammatory events associated with spirochetal diseases.

Evaluation of OspA vaccination-induced serological correlates of protection against Lyme borreliosis in a mouse model

BACKGROUND

For clinical development of a novel multivalent OspA vaccine against Lyme borreliosis, serological assays are required which can be used to establish immune correlates of protection against infection with Borrelia.

METHODS

Four assays (an OspA IgG ELISA, a competitive inhibition (CI) ELISA, a Borrelia surface-binding (SB) assay and a Borrelia killing assay) were used to evaluate the correlation between immune responses induced by rOspA 1/2 (a chimeric immunogen containing protective epitopes from OspA serotypes 1 and 2), and protective immunity against infection by B. burgdorferi s.s. (OspA-1) and B. afzelii (OspA-2). Mice were immunized with OspA 1/2 doses ranging from 0.3 ng to 100 ng, to induce a range of OspA antibody titers, and exposed to needle challenge with B. burgdorferi s.s. or tick challenge with B. afzelii. Receiver operator characteristics (ROC) curves were constructed for each assay, and the area under the curve (AUC), sensitivity, specificity and Youden Index were calculated. Potential cutoff antibody titers which could be used as correlates of vaccine-induced protection were derived from the maximum Youden Index.

RESULTS

Immunization with OspA-1/2 provided dose-dependent protection against infection with B. burgdorferi s.s. and B. afzelii. Antibody responses detected by all four assays were highly significantly correlated with protection from infection by either B. burgdorferi s.s. (p<0.0001 to 0.0062) or B. afzelii (p<0.0001). ROC analyses of the diagnostic effectiveness of each assay showed the AUC to range between 0.95 and 0.79, demonstrating that all assays distinguish well between infected and non-infected animals. Based on sensitivity, specificity and AUC, the OspA IgG ELISA and SB assays best discriminated between infected and non-infected animals.

CONCLUSIONS

All four assays differentiate well between Borrelia-infected and non-infected animals. The relatively simple, high throughput IgG ELISA would be suitable to establish immune correlates of protection for the novel OspA vaccine in clinical trials.

Reservoir targeted vaccine for lyme borreliosis induces a yearlong, neutralizing antibody response to OspA in white-footed mice

Lyme disease is caused by the spirochete Borrelia burgdorferi. The enzootic cycle of this pathogen requires that Ixodes spp. acquire B. burgdorferi from infected wildlife reservoirs and transmit it to other uninfected wildlife. At present, there are no effective measures to control B. burgdorferi; there is no human vaccine available, and existing vector control measures are generally not acceptable to the public. However, if B. burgdorferi could be eliminated from its reservoir hosts or from the ticks that feed on them, the enzootic cycle would be broken, and the incidence of Lyme disease would decrease. We developed OspA-RTV, a reservoir targeted bait vaccine (RTV) based on the immunogenic outer surface protein A (OspA) of B. burgdorferi aimed at breaking the natural cycle of this spirochete. White-footed mice, the major reservoir species for this spirochete in nature developed a systemic OspA-specific IgG response as a result of ingestion of the bait formulation. This immune response protected white-footed mice against B. burgdorferi infection upon tick challenge and cleared B. burgdorferi from the tick vector. In performing extensive studies to optimize the OspA-RTV for field deployment, we determined that mice that consumed the vaccine over periods of 1 or 4 months developed a yearlong, neutralizing anti-OspA systemic IgG response. Furthermore, we defined the minimum number of OspA-RTV units needed to induce a protective immune response.

Human Lyme disease vaccines: past and future concerns

The development of a vaccine for Lyme disease was intensely pursued in the 1990s. However, citing a lack of demand, the first human Lyme disease vaccine was withdrawn from the market less than 5 years after its approval. The public's concerns about the vaccine's safety also likely contributed to the withdrawal of the vaccine. Nearly a decade later, no vaccine for human Lyme disease exists. The expansion of Lyme disease's endemic range, as well as the difficulty of diagnosing infection and the disease's steady increase in incidence in the face of proven preventative measures, make the pursuit of a Lyme disease vaccine a worthwhile endeavor. Many believe that the negative public perception of the Lyme disease vaccine will have tarnished any future endeavors towards its development. Importantly, many of the drawbacks of the Lyme disease vaccine were apparent or foreseeable prior to its approval. These pitfalls must be confronted before the construction of a new, effective and safe human Lyme disease vaccine.

A novel technology for the production of a heterologous lipoprotein immunogen in high yield has implications for the field of vaccine design

We have developed a novel platform technology that can express high levels of recombinant lipoproteins with intrinsic adjuvant properties. In this study, Ag473 (a lipoprotein from Neisseria meningitidis) can be produced in high yields using Escherichia coli strain C43 (DE3). After testing a non-lipoimmunogen (E3, from dengue virus) fused with different lipid signal peptides from other lipoproteins as well as Ag473 fragments of different lengths, we identified that the fusion sequence has to contain at least the N-terminal 40 residues, D1, of Ag473 to achieve high expression levels of the recombinant lipo-immunogen (rlipo-D1E3). The rlipo-D1E3 was found to elicit stronger anti-E3 and virus neutralizing antibody responses in animal studies than those from rE3 alone or rE3 formulated with alum adjuvant. These results have successfully demonstrated the merit of lipo-immunogens for novel vaccine development.

Immunodominant epitope in the C-terminus of a variable major protein in Borrelia duttonii, an agent of tick-borne relapsing fever

Borrelia duttonii strain Ly was isolated from a child with tick-borne relapsing fever in Tanzania. B. duttonii produces variable major proteins (Vmps), which undergo antigenic variation. We previously reported transcription of the vmpP gene, which is one of the Vmp genes in strain Ly, detected in vitro cultivation. In the current study, we purified the recombinant non-lipidated VmpP protein by affinity chromatography and produced VmpP polyclonal antibodies. Antigenicity of VmpP was examined by Western immunoblot analysis and peptide-based enzyme-linked immunosorbent assays. Antigenic epitopes were shown to comprise five regions interspersed within the VmpP primary amino acid sequence. Synthetic peptides spanning residues of three of five regions, 232-237 (LASIVD), 280-285 (AGGIAL), and 350-355 (KAADQQ), reacted strongly with the VmpP-specific antibody and these residues were identified as epitopes. In particular, the C-terminal domain (KAADQQ) of this protein was immunoreactive. Further research based on our results will promote the development of a recombinant vaccine for B. duttonii infection.

Expression and secretion of recombinant outer-surface protein A from the Lyme disease agent, Borrelia burgdorferi, in Nicotiana tabacum suspension cells

The ospA gene of Borrelia burgdorferi codes for an outer membrane lipoprotein, which is a major antigen of the Lyme disease agent. Recombinant OspA vaccines tested so far were expressed in Escherichia coli. In this study, we investigated the expression of a soluble OspA protein in Nicotiana tabacum suspension cells and evaluated the secretion of OspA driven by either its own bacterial signal peptide or a plant signal peptide fused to the amino-terminal cysteine of the mature form. In both cases, the signal peptide was cleaved off and OspA secreted. During secretion, OspA was N-glycosylated. Addition of a C-terminal KDEL sequence led to retention of OspA in the endoplasmic reticulum.

Interleukin-6 promotes anti-OspA borreliacidal antibody production in vitro

Determination of the immunological mediators responsible for promoting the production of borreliacidal antibody may facilitate the development of an improved borreliosis vaccine for human and veterinary use. Previously, we developed an in vitro assay to determine if borreliacidal antibody production could be augmented by treatment with different cytokines. In this study, in vitro treatment of lymph node cells producing borreliacidal antibody with recombinant interleukin-6 (rIL-6) resulted in a fourfold enhancement of anti-OspA borreliacidal antibody. Moreover, rIL-6 enhanced Western immunoblot titers and increased the number of B lymphocytes. In contrast, treatment of anti-OspA borreliacidal antibody-producing cells with anti-IL-6 resulted in a fourfold reduction in borreliacidal activity. Treatment with anti-IL-6 also inhibited enhanced borreliacidal antibody production induced by anti-gamma interferon. These data suggest that IL-6 plays a significant role in the production of anti-OspA borreliacidal antibodies.

Oral vaccine that breaks the transmission cycle of the Lyme disease spirochete can be delivered via bait

Borrelia burgdorferi causes Lyme disease, a potentially debilitating human disease for which no vaccine is currently available. We developed an oral bait delivery system for an anti-B. burgdorferi vaccine based in OspA. Mice were immunized orally via gavage and bait feeding. Challenge was performed via Ixodes scapularis field nymphs carrying multiple B. burgdorferi strains. Vaccination protected 89% of the mice and the systemic immune response was skewed toward IgG2a/2b production. Moreover, this oral vaccine reduced the pathogen in the tick vector by eight-fold. We conclude that this oral vaccine induces a protective systemic immune response against a variety of infectious B. burgdorferi strains found in nature and therefore it can eliminate this zoonotic pathogen from its major host reservoirs. Because we observed elimination of the spirochete from the tick vector, a broad delivery of this oral vaccine to wildlife reservoirs is likely to disrupt the transmission cycle of this pathogen.

Structure-based Design of a Second-generation Lyme Disease Vaccine Based on a C-terminal Fragment of Borrelia burgdorferi OspA

Here, we describe a structure-based approach to reduce the size of an antigen protein for a subunit vaccine. Our method consists of (i) determining the three-dimensional structure of an antigen, (ii) identifying protective epitopes, (iii) generation of an antigen fragment that contains the protective epitope, and (iv) rational design to compensate for destabilization caused by truncation. Using this approach we have successfully developed a second-generation Lyme disease vaccine. Outer surface protein A (OspA) from the Lyme disease spirochete Borrelia burgdorferi elicits protective immunity that blocks transmission of Borrelia from the tick vector to the vaccinated animal, and thus has been a focus of vaccine development. OspA has two globular domains that are connected via a unique single-layer beta-sheet. All anti-OspA monoclonal antibodies that block Borrelia transmission bind to conformational epitopes in the C-terminal domain of OspA, suggesting the possibility of using the C-terminal domain alone as a recombinant protein-based vaccine. The removal of ineffective parts from the OspA antigen may reduce side effects and lead to a safer vaccine. We prepared a C-terminal fragment of OspA by removing approximately 45% of residues from the N terminus. Although the fragment retained the native conformation and affinity to a protective antibody, its vaccine efficacy and conformational stability were significantly reduced with respect to full-length OspA. We successfully stabilized the fragment by replacing amino acid residues involved in buried salt-bridges with residues promoting hydrophobic interactions. The mutations promoted the vaccine efficacy of the redesigned fragment to a level comparable to that of the full-length protein, demonstrating the importance of the antigen stability for OspA's vaccine efficacy. Our strategy should be useful for further refining OspA-based vaccines and developing recombinant vaccines for other diseases.

A fusion product of the complete Borrelia burgdorferi outer surface protein A (OspA) and the hepatitis B virus capsid protein is highly immunogenic and induces protective immunity similar to that seen with an effective lipidated OspA vaccine formula

The immunogenicity of peptides and protein fragments can be considerably enhanced by their presentation on particulate carriers such as capsid-like particles (CLP) from hepatitis B virus (HBV). Here we tested the suitability of the HBV capsid protein as a carrier for a relevant full-length pathogen-derived protein antigen. The entire 255-amino acid ectodomain of the outer surface protein A (OspA) from Borrelia burgdorferi, the causative agent of Lyme disease, was inserted into the major B cell epitope of the HBV capsid, yielding a multimerization-competent fusion protein, termed coreOspA. CoreOspA, consisting only in part of regular CLP, induced antibodies to OspA, including the Ig isotype profile and specificity for the protective epitope LA-2, with an efficiency similar to that of recombinant lipidated OspA, the first generation vaccine against Lyme disease. Moreover, coreOspA actively and passively protected mice against subsequent challenge with B. burgdorferi. The data demonstrate the capacity of the HBV capsid protein to act as a potent immunomodulator even for full-length and structurally complex polypeptide chains and thus opens new avenues for novel vaccine designs.

Neutralization of gamma interferon augments borreliacidal antibody production and severe destructive Lyme arthritis in C3H/HeJ mice

Development of a high level of sustained borreliacidal antibody is paramount for maintaining protection against infection with Borrelia burgdorferi. We show that production of borreliacidal antibody can be enhanced by preventing the effects of gamma interferon (IFN-gamma). When lymph node cells capable of producing borreliacidal antibody were cultured with anti-murine IFN-gamma, an eightfold increase in borreliacidal antibody production was obtained. However, anti-IFN-gamma treatment of these cells also enhanced their ability to adaptively induce arthritis. When anti-IFN-gamma-treated lymph node cells producing borreliacidal antibody were infused into C3H/HeJ mice and the mice were then challenged with B. burgdorferi, the mice developed severe destructive Lyme arthritis. Additional studies are needed to delineate the immune response responsible for the induction of arthritis and production of borreliacidal antibody. These studies are needed to ensure an effective and safe vaccine against infection with B. burgdorferi.

Structural identification of a key protective B-cell epitope in Lyme disease antigen OspA

Outer surface protein A (OspA) is a major lipoprotein of the Borrelia burgdorferi spirochete, the causative agent of Lyme disease. Vaccination with OspA generates an immune response that can prevent bacterial transmission to a mammalian host during the attachment of an infected tick. However, the protective capacity of immune sera cannot be predicted by measuring total anti-OspA antibody. The murine monoclonal antibody LA-2 defines an important protective B-cell epitope of OspA against which protective sera have strong levels of reactivity. We have now mapped the LA-2 epitope of OspA using both NMR chemical-shift perturbation measurements in solution and X-ray crystal structure determination. LA-2 recognizes the three surface-exposed loops of the C-terminal domain of OspA that are on the tip of the elongated molecule most distant from the lipid-modified N terminus. The structure suggests that the natural variation at OspA sequence position 208 in the first loop is a major limiting factor for antibody cross-reactivity between different Lyme disease-causing Borrelia strains. The unusual Fab-dominated lattice of the crystal also permits a rare view of antigen flexibility within an antigen:antibody complex. These results provide a rationale for improvements in OspA-based vaccines and suggest possible designs for more direct tests of antibody protective levels in vaccinated individuals.

Detection of borreliacidal antibodies in dogs after challenge with Borrelia burgdorferi-infected ixodes scapularis ticks

Detection of borreliacidal antibodies is an accurate serodiagnostic test for confirmation of Lyme disease in humans. In this study, 13 pathogen-free beagles, 12 to 26 weeks old, were infected with Borrelia burgdorferi by tick challenge. Dogs were monitored for clinical signs and symptoms of Lyme disease along with borreliacidal antibody production against B. burgdorferi sensu stricto isolates 297 and 50772. Ten (77%) dogs developed lameness in one or more legs within 210 days after attachment of Ixodes scapularis ticks. Eight (80%) of the lame animals had concurrent fever of > or =38 degrees C. Spirochetes were also recovered from the skin and joints of 12 (92%) dogs, but rarely from other organs. Borreliacidal antibodies against B. burgdorferi isolate 297 were detected in only four (31%) dogs, and the levels of killing antibodies remained low for the duration of the infection. In contrast, borreliacidal antibodies against B. burgdorferi isolate 50772 were detected in 13 (100%) dogs within 21 days of infection. Furthermore, the borreliacidal antibody levels correlated with the severity of B. burgdorferi infection. Detection of borreliacidal antibodies, especially against B. burgdorferi isolate 50772, is also a reliable serodiagnostic test for detection of Lyme disease in dogs.

Specific immune response to a synthetic peptide derived from outer surface protein C of Borrelia burgdorferi predicts protective borreliacidal antibodies

In a previous study, we described the development of a new specific serodiagnostic test for Lyme disease involving enzyme-linked immunosorbent assay and a synthetic peptide, OspC-I. The OspC-I peptide is derived from part of the outer surface protein C (OspC) amino acid sequence of Borrelia burgdorferi and is located in the region conserved among B. burgdorferi sensu stricto or sensu lato isolates. In this study, we demonstrate that sera containing antibodies against OspC-I from patients with early Lyme disease had borreliacidal activity against isolates of three genospecies of Lyme disease spirochete, B. burgdoreferi B31, B. garinii HPI and B. afzelii HT61. However, the borreliacidal activity against B. burgdorferi, which has not been isolated in Japan, was weaker than that against the other species. Vaccination of mice with OspC-I induced the production of anti-OspC-I antibodies in serum with borreliacidal activity. The immune mouse serum had significantly higher levels of borreliacidal activity against HP1 and HT61, than against B31. Neutralization of borreliacidal activity with anti-IgM antibodies showed that the borreliacidal activity of anti-OspC-I antibodies in serum was due to IgM. Furthermore. mice vaccinated with OspC-I were protected against challenge with HPI and HT61. but not fully protected against infection with B31. These results suggest that OspC-I is not only a specific antigen for use in serodiagnostic tests for Lyme disease, but is also a potential candidate for a Lyme disease vaccine in Japan.

The lipid component of lipoproteins from Borrelia burgdorferi: structural analysis, antigenicity, and presentation via human dendritic cells

The spirochaetal bacteria Borrelia burgdorferi (Bb) is the tick-borne causative agent of lyme disease. The major membrane immunogens of Bb are outer surface proteins. The lipid component of these lipoproteins is relevant for the immunogenicity of Bb-lipoproteins. To characterize the antigenic properties, the native lipid component of lipoproteins was isolated and the detailed molecular structure was analyzed. The molecular structure of the lipoprotein-lipid component turned out to be S(propane-2',-3'diol)-3-thio-2-aminopropanic acid (S-glyceryl-cysteine) with one ester-linked fatty acid, one acetyl group, and one N-terminal amide-bound fatty acid. Fatty acid analysis of the lipid component indicated a heterogeneous composition comprising C16:0, C18:0, C18:1, C18:2, and C 20:0. The antigenicity was tested with in vitro bioassays using human blood-derived dendritic cells (DCs) as antigen-presenting cells and autologous Bb-specific T-cells. We found that human DCs present the lipid component of Bb-lipoproteins via MHC class II inducing an antigen-specific T-cell immune response in vitro.

Lyme disease prevention and vaccine prophylaxis

OBJECTIVE

To provide a comprehensive review of the epidemiology, diagnosis, and prevention of Lyme disease with a focus on the Lyme disease vaccine.

DATA SOURCE

A computerized search of MEDLINE (January 1996-December 1998) was used to identify articles regarding Lyme disease, Borrelia burgdorferi, epidemiology, prevention, and vaccine.

DATA SYNTHESIS

Lyme disease is a condition caused by infection with B. burgdorferi. The organism is carried by certain species of Ixodes ticks and is the most common tick-borne disease in the US. In patients with clinical manifestations of Lyme disease, various pharmacotherapeutic approaches have proven effective in treatment of the clinical features. Prevention strategies exist; however, their application is sometimes difficult. A vaccine for the prevention of Lyme disease is available, and another is being considered for approval. The recombinant outer surface protein A (OspA) vaccines to prevent Lyme disease are immunogenic and have an acceptable adverse effect profile. These vaccines are highly efficacious for the prevention of Lyme disease.

CONCLUSIONS

Lyme disease is the most common tick-borne disease in the US. The infection, caused by B. burgdorferi, results in dermatologic, neurologic, cardiovascular, and musculoskeletal manifestations. Until recently, tick bite prevention strategies were the only means of decreasing the risk of acquiring the infection. The OspA vaccines are efficacious for the prevention of infection. Although universal immunization with these vaccines is unlikely, the availability of effective vaccines represents an important tool for the prevention of Lyme disease in endemic regions of the US.

Vaccination as a modality to prevent Lyme disease. A status report

Recombinant outer surface protein A (OspA) of Borrelia burgdorferi is a highly protective immunogen for prevention of Lyme disease in experimental animals. Humoral immunity is sufficient for protection. The principal mechanism of action is prevention of transmission of the spirochete from tick to host. A recombinant OspA vaccine has been licensed for use in dogs. The recent licensure of an OspA vaccine for humans resulted from a critical analysis of recently completed efficacy studies.

Molecular analysis of sequence heterogeneity among genes encoding decorin binding proteins A and B of Borrelia burgdorferi sensu lato

Immunization of mice with Borrelia burgdorferi decorin binding protein A (DbpA), one of two gene products of the dbpBA locus, has been shown recently to confer protection against challenge. Hyperimmune DbpA antiserum killed a large number of B. burgdorferi sensu lato isolates of diverse phylogeny and origin, suggesting conservation of the protective epitope(s). In order to evaluate the heterogeneity of DbpA and DbpB and to facilitate defining the conserved epitope(s) of these antigens, the sequences of the dbpA genes from 29 B. burgdorferi sensu lato isolates and of the dbpB genes from 15 B. burgdorferi sensu lato isolates were determined. The predicted DbpA sequences were fairly heterogeneous among the isolates (58.3 to 100% similarity), but DbpA sequences with the highest similarity tended to group into species previously defined by well-characterized chromosomal markers. In contrast, the predicted DbpB sequences were highly conserved (96.3 to 100% similarity). Substantial diversity in DbpA sequence was seen among isolates previously shown to be killed by antiserum against a single DbpA, suggesting that one or more conserved protective epitopes are composed of noncontiguous amino acids. The observation of individual dbpA alleles with sequence elements characteristic of more than one B. burgdorferi sensu lato species was consistent with a role for genetic recombination in the generation of dbpA diversity.

NMR identification of epitopes of Lyme disease antigen OspA to monoclonal antibodies

Outer surface protein A (OspA) from the Lyme disease spirochete Borrelia burgdorferi has been a focus of vaccine development. We have identified epitopes of OspA to two monoclonal antibodies (mAbs) by comparing NMR chemical shifts of free OspA and those in Fab complexes. Deuteration of non-labile protons in OspA extended the size limit of this technique so that it was applicable to the 78 kDa complexes of OspA and the Fab fragment. The epitope identified by NMR to an mAb, 184.1, agrees well with that previously defined by the crystal structure of the same complex, indicating the ability of the NMR method to accurately map an epitope in a large protein complex. The technique mapped the epitope to mAb 336, a mAb of clinical interest, to a region centered at the C-terminal alpha-helix. The results provides a basis for rational design of OspA-based Lyme disease vaccines.

Active and passive immunity against Borrelia burgdorferi decorin binding protein A (DbpA) protects against infection

Borrelia burgdorferi, the spirochete that causes Lyme disease, binds decorin, a collagen-associated extracellular matrix proteoglycan found in the skin (the site of entry for the spirochete) and in many other tissues. Two borrelial adhesins that recognize this proteoglycan, decorin binding proteins A and B (DbpA and DbpB, respectively), have recently been identified. Infection of mice by low-dose B. burgdorferi challenge elicited antibodies against DbpA and DbpB that were sustained at high levels, suggesting that these antigens are expressed in vivo. Scanning immunoelectron microscopy showed that DbpA was surface accessible on intact borreliae. Passive administration of DbpA antiserum protected mice from infection following challenge with heterologous B. burgdorferi sensu stricto isolates, even when serum administration was delayed for up to 4 days after challenge. DbpA is the first antigen target identified that is capable of mediating immune resolution of early, localized B. burgdorferi infections. DbpA immunization also protected mice from B. burgdorferi challenge; DbpB immunization was much less effective. DbpA antiserum inhibited in vitro growth of many B. burgdorferi sensu lato isolates of diverse geographic, phylogenetic, and clinical origins. In combination, these findings support a role for DbpA in the immunoprophylaxis of Lyme disease and suggest that DbpA vaccines have the potential to eliminate early-stage B. burgdorferi infections.

T helper cell priming of mice to Borrelia burgdorferi OspA leads to induction of protective antibodies following experimental but not tick-borne infection

Antibodies to the outer surface lipoprotein A (OspA) of Borrelia burgdorferi confer protection to SCID mice against subsequent tick-borne or experimental infection. However, OspA-specific antibodies are hardly detectable in naturally infected humans, dogs, hamsters and mice. This is most probably due to limited expression of OspA on spirochetes transmitted from the vector to the host. Here we have tested whether T cell priming of mice would lead to the induction of protective OspA-specific antibodies upon infection. It is shown that AKR/N mice, previously immunized with either a single T helper cell peptide of OspA, or a mixture of 27 peptides spanning the entire molecule, develop OspA-specific IgM or IgG antibodies, including those to a prominent protective B cell epitope of OspA. LA-2, within 7 days of infection with low doses (10(3)) of culture-derived spirochetes. In marked contrast, the same groups of pre-sensitized mice failed to generate any detectable OspA-specific antibodies after tick-borne infection for more than 40 days after infection. All mice, irrespective of their state of T cell immunity to OspA or the mode of infection, produced similar levels of OspC-specific IgM and IgG antibodies as early as day 14 after infection. None of the mice previously immunized with OspA peptides were protected against experimental infection, in spite of the appearance of protective antibodies. It is clear from these data that, in contrast to culture-derived spirochetes, the naturally transmitted pathogen fails to express OspA within the mammalian host at levels sufficient for induction of B cell responses, even in the presence of pre-activated T helper cells. Together with the fact that OspA-specific antibodies are mainly operative by eliminating spirochetes from the vector during infestation, the data suggest that OspA-vaccination for T helper cell immunity alone is not sufficient to prevent Lyme disease.

Vaccination of natural reservoir hosts with recombinant lipidated OspA induces a transmission-blocking immunity against Lyme disease spirochaetes associated with high levels of LA-2 equivalent antibodies

As observed in humans, immune responses in naturally infected reservoir hosts of Borrelia burgdorferi sensu lato rarely target the outer surface proteins (Osp) A and B of Lyme disease spirochaetes. The absence of protective immunity in such hosts following tick-borne infection allows them to play an effective role in the maintenance of Lyme borreliosis in nature. Therefore, the question was addressed whether one of the most prominent natural reservoir host species of B. burgdorferi s.l. in Europe, the yellow-necked mouse (Apodemus flavicollis), may lack the ability to elicit transmission-blocking antibodies to Lyme borreliosis spirochaetes. Yellow-necked mice were immunized with a recombinant lipidated OspA from B. burgdorferi sensu stricto or with high numbers of UV-irradiated whole spirochaetes. All immunized mice, but not untreated controls, developed polyclonal humoral immune responses to OspA (31 kDa). Serum antibodies of animals vaccinated with the recombinant OspA contained high levels of antibody to an epitope of OspA, defined by the monoclonal antibody LA-2, whereas only low levels of LA-2 equivalent antibodies could be detected in sera from animals immunized with killed spirochaetes. Ixodes ricinus ticks infected with B. burgdorferi s.s. lost their spirochaete load after feeding on animals with high levels of LA-2 equivalent antibody; ticks feeding on animals which had only low or undetectable serum levels of LA-2 equivalent antibodies retained their spirochaete infection. Furthermore, animals with high levels of LA-2 equivalent antibody were protected against spirochaete infection. Our study shows that natural mouse reservoir hosts are highly competent to generate transmission-blocking antibodies after vaccination with a lipidated recombinant OspA and indicates that antibodies to the LA-2 epitope play a key role in the destruction of B. burgdorferi s.s. within feeding Ixodes ricinus ticks.

OspA lipoprotein of Borrelia burgdorferi is a mucosal immunogen and adjuvant

The outer surface protein A (OspA) lipoprotein of Borrelia burgdorferi, like cholera toxin and the heat-labile enterotoxin of Escherichia coli, induces pro-inflammatory cytokines. This suggested that, like those toxins, OspA might be a mucosal immunogen and adjuvant. OspA, administered intranasally (i.n.) or intragastrically, induced strong serum IgG and salivary gland IgA responses. The serum IgG isotypes were indicative of a mixed T helper 1 and T helper 2 response, the latter being more pronounced. The N-terminal tripalmitoyl-S-glyceryl-cysteine (Pam3Cys) lipid moiety was absolutely required. OspA strongly enhanced the serum IgG and salivary gland IgA responses to jack bean urease co-administered by the i.n. route. OspA also enhanced the response to tetanus toxoid and induced limited protection against challenge. A synthetic lipopeptide also adjuvanted the response to urease by the i.n. route, but was ca 500-fold less potent on a molar basis than OspA. These results suggest that OspA or other lipoproteins may be useful in mucosal vaccines.

Acquired resistance to Borrelia burgdorferi infection in the rabbit. Comparison between outer surface protein A vaccine- and infection-derived immunity

Intradermal inoculation of the rabbit with Borrelia burgdorferi, sensu lato, results in the consistent development of erythema migrans (EM), dermal infection, and visceral dissemination of the spirochete. Within 5 mo, EM as well as dermal and visceral infection are cleared and the animals exhibit immunity to reinfection. This study compares infection-derived immunity with acquired resistance resulting from the administration of a lipidated recombinant outer surface protein A (OspA) vaccine presently undergoing human trial. 4 of 11 OspA vaccinated rabbits, challenged intradermally at each of 10 sites with 10(5) low passage B. burgdorferi, developed EM as well as dermal and disseminated infection. After identical challenge, 2 of the 11 infection-immune rabbits developed a dermal infection, but not EM or disseminated infection. Further, ELISA anti-OspA titers did not correlate with the status of immunity for either OspA vaccinated or infection-immune rabbits. Prechallenge ELISA anti-OspA titers were relatively low in the infection-immune group. This study demonstrates that a state of partial immunity to experimental Lyme disease may result that could potentially mask infection. Further, our data strongly suggest that immunogen(s) other than OspA is/are responsible for stimulating acquired resistance in the infection-immune rabbit.

Crystal structure of Lyme disease antigen outer surface protein A complexed with an Fab

OspA (outer surface protein A) is an abundant immunogenic lipoprotein of the Lyme disease spirochete Borrelia burgdorferi. The crystal structure of a soluble recombinant form of OspA was solved in a complex with the Fab fragment of mouse monoclonal antibody 184.1 and refined to a resolution of 1.9 A. OspA has a repetitive antiparallel beta topology with an unusual nonglobular region of "freestanding" sheet connecting globular N- and C-terminal domains. Arrays of residues with alternating charges are a predominant feature of the folding pattern in the nonglobular region. The 184.1 epitope overlaps with a well conserved surface in the N-terminal domain, and a hydrophobic cavity buried in a positively charged cleft in the C-terminal domain is a potential binding site for an unknown ligand. An exposed variable region on the C-terminal domain of OspA is predicted to be an important factor in the worldwide effectiveness of OspA-based vaccines.

Reactivity with a specific epitope of outer surface protein A predicts protection from infection with the Lyme disease spirochete, Borrelia burgdorferi

The response to recombinant vaccines for Lyme disease was studied to determine serum antibody levels effective in protecting against tick-transmitted infection. Data presented here demonstrate a significant correlation between antibody to an epitope on outer surface protein A (OspA) and protection against infection with Borrelia burgdorferi in canines and mice. A competitive enzyme-linked immunosorbent assay was developed to measure antibody to a site on OspA, defined by monoclonal antibody LA-2. Comparison of LA-2 titers against infection of canines and mice following vaccination and challenge established a predicted value for LA-2 titers. The statistical relationship between serum antibody levels and protection was calculated by logistic regression analysis. The statistical model predicted that an LA-2 titer of 0.32 microg equivalents (eq) per ml correlated to an 80% predicted probability of protection for both mice and dogs. This value was used to classify mice and dogs as to their protected status at the time of tick exposure. The LA-2 cutoff titer (0.32 microg eq/ml) correctly classified all dogs (n = 13) and mice (n = 44) that failed to become infected. By contrast, 20 of 22 dogs and 28 of 31 mice with titers of less than 0.32 microg eq/ml became infected. On the basis of these results, we conclude that an LA-2 titer is a reliable indicator of immune status for estimating immune protection following use of OspA-based vaccines for B. burgdorferi sensu stricto.

Lyme disease: a review of aspects of its immunology and immunopathogenesis

Lyme disease, caused by Borrelia burgdorferi, causes a multisystem inflammatory ailment, although the precise means of tissue damage are not well understood. It is clear that the organism is present at the site of inflammation in many organs and that many of the features of the illness are relieved by antibiotic therapy. A complex interaction between spirochete and immune systems of a number of mammalian hosts, in human disease and animal models, has been described. It is clear that T cells and macrophages are intimately associated with the pathogenesis of arthritis and that immune mechanisms are involved in other aspects of disease. Inflammation directed at persistence of Borrelial antigens is a plausible explanation for persisting arthritis. Autoimmunity based on molecular mimicry may play a role in the pathogenesis of Lyme disease. Humoral immunity plays a protective role, prompting interest in vaccine development. Significant variation in certain of the outer surface proteins suggests that multiple proteins, peptides, or chimeric vaccines may be needed to provide a sufficiently broad humoral protective response.

Protective immunization with plasmid DNA containing the outer surface lipoprotein A gene of Borrelia burgdorferi is independent of an eukaryotic promoter

Plasmid DNA encoding the outer surface lipoprotein A (OspA) of Borrelia burgdorferi under the control of either strong eukaryotic/viral or its own bacterial promoter was injected intramuscularly (m. tibialis anterior) or intradermally into BALB/c and AKR/N mice. OspA-specific antibodies and OspA-reactive T helper 1 cells (Th1) were induced only with those plasmids containing the ospA structural gene including its own regulatory control region immediately upstream. In the absence of the ospA promoter, no or only marginal immune responses to OspA were obtained, even when strong eukaryotic promoter/enhancer elements were present. Together with the finding that the ospA promoter is active in a mouse B-lymphoma line, the data suggest that spirochetes are able to express at least part of their genes in the mammalian environment. Mice previously vaccinated with the relevant ospA plasmid DNA were protected against subsequent experimental challenge with a virulent strain of B. burgdorferi, as measured by the appearance of antibodies to a prominent protective epitope (LA-2) and the failure to re-isolate spirochetes from ear biopsies. In addition, C.B-17 severe-combined immunodeficient mice could be protected against infection by passive transfer of immune sera from ospA plasmid DNA-inoculated normal mice. Protective LA-2-related antibody titers obtained after repeated immunization persisted for 200 days and longer. This simple procedure of immunization using plasmid DNA consisting of a prokaryotic gene under the control of its own promoter holds great promise for the development of alternative subunit vaccines against bacterial infections, including Lyme disease. In addition, the availability of this novel prokaryotic promoter element now allows the study of the basis for the differential expression of bacterial genes in prokaryotic and eukaryotic environments.

Resistance to tick-borne spirochete challenge induced by Borrelia burgdorferi strains that differ in expression of outer surface proteins

Hamsters were immunized with thimerosal-killed Borrelia burgdorferi 297 or a mutant of 297 (M297) that lacks the 49-kb linear plasmid and expression of outer surface proteins A and B (OspA and OspB). Ixodes scapularis nymphs infected with either the B. burgdorferi sensu stricto strain 297 or JMNT, similar in OspA and OspB but differing in OspC expression, were used to evaluate protection. In a homologous challenge, 24 hamsters were vaccinated, 8 each with 297 or M297 and 8 sham (adjuvant)-vaccinated controls. Hamsters vaccinated with either bacterin were completely protected against a natural tick bite or subcutaneous (s.c.) inoculation of 297. Borreliae were effectively eliminated from 80 to 90% of the 297-infected ticks that fed on four hamsters immunized with the 297 bacterin. Cultures of spirochetes isolated from the ticks that remained infected were infectious and induced joint inflammation in naive hamsters. There was no reduction of strain 297 spirochetes in ticks that fed on four hamsters immunized with M297, but the hamsters were protected. Results with the M297 bacterin indicate that proteins other than OspA or OspB can protect hamsters against a tick challenge without eliminating B. burgdorferi in the tick. In a heterologous challenge, 36 hamsters were vaccinated, 12 with each bacterin and 12 controls. None of the hamsters immunized with either bacterin were protected from a challenge involving JMNT-infected ticks, while two of four were protected against an s.c. challenge. Hamsters challenged s.c. with strain 297 spirochetes were protected. There was partial elimination of JMNT spirochetes in ticks that fed on the group of four hamsters immunized with the 297 bacterin, and infection rates were reduced by 50 to 60%. JMNT spirochetes reisolated from the ticks that fed on 297-vaccinated hamsters also remained infectious for hamsters. In the JMNT-infected ticks that fed on four M297-immunized hamsters, there was no decline in the proportion of infected ticks. Destruction of spirochetes in ticks that fed on the hamsters vaccinated with the 297 bacterin suggests that antibodies to OspA and OspB may have been responsible, since the mutant did not induce this activity.

Immunity to Lyme disease: protection, pathology and persistence

Persistence of the Lyme disease spirochete, Borrelia burgdorferi, in the presence of an active immune response has been well documented. Evidence from the past year indicates that modulation of surface antigens by the spirochete may be a major mechanism for evading the immune response.

Dominant recognition of a Borrelia burgdorferi outer surface protein A peptide by T helper cells in patients with treatment-resistant Lyme arthritis

In an earlier study, we found that T-cell lines (TCL) from five patients with treatment-resistant Lyme arthritis preferentially recognized Borrelia burgdorferi outer surface protein A (OspA), but TCL from four patients with treatment-responsive arthritis only rarely recognized this protein. Dominant T-cell recognition of an arthritogenic OspA epitope is one way in which the immune response against OspA might be involved in the pathogenesis of treatment-resistant Lyme arthritis. In an effort to test this hypothesis, we mapped the epitopes of 31 OspA-specific TCL and five T-cell clones derived from the synovial fluid or peripheral blood samples of three patients with treatment-resistant Lyme arthritis. Although each patient's TCL recognized a broad array of OspA peptides with different individual patterns, two regions of OspA were dominantly recognized. Each patient's TCL dominantly recognized a C-terminal epitope of OspA, ranging from amino acids (aa) 214 to 233 in one patient to 244 to 263 in another, and the TCL of all three patients dominantly recognized an epitope between aa 84 and 113. These dominant regions were confirmed by clonal analysis in one patient. Thus, the region of OspA between aa 84 and 113 was the dominant T-cell epitope shared by these three patients with treatment-resistant Lyme arthritis. If the T-cell response to OspA is involved in the pathogenesis of treatment-resistant Lyme arthritis, and epitope contained within aa 84 to 113 is a potentially arthritogenic epitope.