Molecular mimetics of polysaccharide epitopes as vaccine candidates for prevention of Neisseria meningitidis serogroup B disease

Controlling serogroup B invasive meningococcal disease: the Canadian perspective

With publically funded meningococcal immunization programs established in infants, children and adolescents, Canada is at the forefront of invasive meningococcal disease prevention. The advent of two new serogroup B vaccines that may protect against multiple disease-causing strains offers the potential to reduce endemic disease to very low levels in Canada. Canada likely will be one of the first countries with approval to use recombinant serogroup B vaccine. However, inclusion of these new vaccines into public immunization programs will be decided at the provincial/territorial level, rather than nationally, and may result initially in different immunization schedules throughout the country as we have seen with conjugate meningococcal vaccines. Such heterogeneous use and adoption of new vaccines complicates disease control, but may assist in evaluation of effectiveness. Minimally, it requires regionally specific information. In this article, the authors provide an overview of the Canadian epidemiology, serogroup B vaccine characteristics, potential strain coverage, immunization strategies and remaining postmarketing research questions.

The K1 capsular polysaccharide from Acinetobacter baumannii is a potential therapeutic target via passive immunization

The emergence of extremely resistant and panresistant Gram-negative bacilli, such as Acinetobacter baumannii, requires consideration of nonantimicrobial therapeutic approaches. The goal of this report was to evaluate the K1 capsular polysaccharide from A. baumannii as a passive immunization target. Its structure was determined by a combination of mass spectrometric and nuclear magnetic resonance (NMR) techniques. Molecular mimics that might raise the concern for autoimmune disease were not identified. Immunization of CD1 mice demonstrated that the K1 capsule is immunogenic. The monoclonal antibody (MAb) 13D6, which is directed against the K1 capsule from A. baumannii, was used to determine the seroprevalence of the K1 capsule in a collection of 100 A. baumannii strains. Thirteen percent of the A. baumannii isolates from this collection were seroreactive to MAb 13D6. Opsonization of K1-positive strains, but not K1-negative strains, with MAb 13D6 significantly increased neutrophil-mediated bactericidal activity in vitro (P < 0.05). Lastly, treatment with MAb 13D6 3 and 24 h after bacterial challenge in a rat soft tissue infection model resulted in a significant decrease in the growth/survival of a K1-positive strain compared to that of a K1-negative strain or to treatment with a vehicle control (P < 0.0001). These data support the proof of principle that the K1 capsule is a potential therapeutic target via passive immunization. Other serotypes require assessment, and pragmatic challenges exist, such as the need to serotype infecting strains and utilize serotype-specific therapy. Nonetheless, this approach may become an important therapeutic option with increasing antimicrobial resistance and a diminishing number of active antimicrobials.

Ending the drought: new strategies for improving the flow of affordable, effective antivenoms in Asia and Africa

The development of snake antivenoms more than a century ago should have heralded effective treatment of the scourge of snakebite envenoming in impoverished, mostly rural populations around the world. That snakebite still exists today, as a widely untreated illness that maims, kills and terrifies men, women and children in vulnerable communities, is a cruel anachronism. Antivenom can be an effective, safe and affordable treatment for snakebites, but apathy, inaction and the politicisation of public health have marginalised both the problem (making snakebite arguably the most neglected of all neglected tropical diseases) and its solution. For lack of any coordinated approach, provision of antivenoms has been pushed off the public health agenda, leading to an incongruous decline in demand for these crucial antidotes, excused and fed by new priorities, an absence of epidemiological data, and a poor regulatory framework. These factors facilitated the infiltration of poor quality products that degrade user confidence and undermine legitimate producers. The result is that tens of thousands are denied an essential life-saving medicine, allowing a toll of human suffering that is a summation of many individual catastrophes. No strategy has been developed to address this problem and to overcome the intransigence and inaction responsible for the global tragedy of snakebite. Attempts to engage with the broader public health community through the World Health Organisation (WHO), GAVI, and other agencies have failed. Consequently, the toxinology community has taken on a leadership role in a new approach, the Global Snakebite Initiative, which seeks to mobilise the resources, skills and experience of scientists and clinicians for whom venoms, toxins, antivenoms, snakes and snakebites are already fields of interest. Proteomics is one such discipline, which has embraced the potential of using venoms in bio-discovery and systems biology. The fields of venomics and antivenomics have recently evolved from this discipline, offering fresh hope for the victims of snakebites by providing an exciting insight into the complexities, nature, fundamental properties and significance of venom constituents. Such a rational approach brings with it the potential to design new immunising mixtures from which to raise potent antivenoms with wider therapeutic ranges. This addresses a major practical limitation in antivenom use recognised since the beginning of the 20th century: the restriction of therapeutic effectiveness to the specific venom immunogen used in production. Antivenomic techniques enable the interactions between venoms and antivenoms to be examined in detail, and if combined with functional assays of specific activity and followed up by clinical trials of effectiveness and safety, can be powerful tools with which to evaluate the suitability of current and new antivenoms for meeting urgent regional needs. We propose two mechanisms through which the Global Snakebite Initiative might seek to end the antivenom drought in Africa and Asia: first by establishing a multidisciplinary, multicentre, international collaboration to evaluate currently available antivenoms against the venoms of medically important snakes from specific nations in Africa and Asia using a combination of proteomic, antivenomic and WHO-endorsed preclinical assessment protocols, to provide a validated evidence base for either recommending or rejecting individual products; and secondly by bringing the power of proteomics to bear on the design of new immunising mixtures to raise Pan-African and Pan-Asian polyvalent antivenoms of improved potency and quality. These products will be subject to rigorous clinical assessment. We propose radically to change the basis upon which antivenoms are produced and supplied for the developing world. Donor funding and strategic public health alliances will be sought to make it possible not only to sustain the financial viability of antivenom production partnerships, but also to ensure that patients are relieved of the costs of antivenom so that poverty is no longer a barrier to the treatment of this important, but grossly neglected public health emergency.

Effect of human serum on de-N-acetyl sialic acid epitope expression and antibody activity against N. meningitidis group B

Antibody-mediated complement-dependent bactericidal activity (BCA) against Neisseria meningitidis (Nm) is correlated with protection against invasive disease. Recently, we showed that murine antibodies elicited by neuraminic acid-containing polysialic acid (NeuPSA) antigens conferred protection against Nm group B (NmB) strains in an infant rat model of meningococcal bacteremia [Moe GR, Bhandari TS, Flitter BA. Vaccines containing de-N-acetyl sialic acid elicit antibodies protective against neisseria meningitidis groups B and C. J Immunol 2009;182(10):6610-7]. However, NeuPSA antibodies did not mediate BCA against NmB strains in vitro despite the presence of NmB-reactive IgG and IgM. Using monoclonal antibodies (mAbs) SEAM 2 and 3, which are reactive with two distinctive NeuPSA epitopes, and an NmB anticapsular mAb, we show that growth in human serum affects expression of NeuPSA epitopes by NmB and is necessary for evaluating anti-NeuPSA functional activity.

Characterization of a novel protective monoclonal antibody that recognizes an epitope common to Vibrio cholerae Ogawa and Inaba serotypes

A novel protective monoclonal antibody (mAb) that recognizes a lipopolysaccharide (LPS) epitope common between serotypes Ogawa and Inaba of the O1 serogroup of Vibrio cholerae was characterized and the potential to develop peptide mimics of this protective LPS epitope was investigated. mAb 72.1 recognizes both Ogawa and Inaba LPS and it is vibriocidal and protective in passive immunization against infection by strains of both serotypes. The cDNA-derived amino acid sequence of mAb 72.1 is closely related to the previously characterized mAb ZAC-3, which is thought to recognize an epitope in the lipid A core region of O1 LPS. In an attempt to develop a peptide mimic-based vaccine against V. cholerae, phage display libraries were screened with mAb 72.1 and 11 peptide mimics were identified. Remarkably, all of the peptide sequences identified from linear phage display libraries contained two cysteine residues, suggesting that mAb 72.1 preferentially binds to peptides constrained with a disulphide bond. One of the peptide mimics was immunologically characterized. Although immunization of mice with this peptide mimic conjugated to KLH elicited antibodies against the peptide itself, these antibodies did not cross-react with Ogawa or Inaba LPS. Effectiveness of a peptide mimic as a vaccine may depend on how well the peptide can mimic the carbohydrate interactions when binding to the anti-carbohydrate antibody. Thus, investigating how peptides and LPS bind to mAb 72.1 may be useful in improving current peptide mimics or designing more effective peptide mimics. Identification and characterization of novel protective anti-LPS antibodies may be useful in studying protective epitopes of LPS, which may help develop LPS-based therapeutics against V. cholerae.

Vaccines containing de-N-acetyl sialic acid elicit antibodies protective against neisseria meningitidis groups B and C

Murine mAbs that were produced by immunization with a vaccine containing the N-propionyl derivative of Neisseria meningitidis group B (MenB) capsular polysaccharide (NPr MBPS) mediate protective responses against MenB but were not reactive with unmodified MBPS or chemically identical human polysialic acid (PSA). Recently, we showed that some of the mAbs were reactive with MBPS derivatives that contain de-N-acetyl sialic acid residues. In this study we evaluated the immunogenicity of de-N-acetyl sialic acid-containing derivatives of PSA (de-N-acetyl PSA) in mice. Four de-N-acetyl PSA Ags were prepared and conjugated to tetanus toxoid, including completely de-N-acetylated PSA. All of the vaccines elicited anti-de-N-acetyl PSA responses (titers >/=1/10,000), but only vaccines enriched for nonreducing end de-N-acetyl residues by treatment with exoneuraminidase or complete de-N-acetylation elicited high titers against the homologous Ag. Also, nonreducing end de-N-acetyl residue-enriched vaccines elicited IgM and IgG Abs of all subclasses that could bind to MenB. The results suggest that the zwitterionic characteristic of neuraminic acid, particularly at the nonreducing end, may be important for processing and presentation mechanisms that stimulate T cells. Abs elicited by all four vaccines were able to activate deposition of human complement proteins and passively protect against challenge by MenB in the infant rat model of meningococcal bacteremia. Some vaccine antisera mediated bactericidal activity against a N. meningitidis group C strain with human complement. Thus, de-N-acetyl PSA Ags are immunogenic and elicit Abs that can be protective against MenB and N. meningitidis group C strains.

Structural and functional studies of Peptide-carbohydrate mimicry

Certain peptides act as molecular mimics of carbohydrates in that they are specifically recognizedby carbohydrate-binding proteins. Peptides that bind to anti-carbohydrate antibodies, carbohydrate-processingenzymes, and lectins have been identified. These peptides are potentially useful as vaccines andtherapeutics; for example, immunologically functional peptide molecular mimics (mimotopes) can strengthenor modify immune responses induced by carbohydrate antigens. However, peptides that bind specificallyto carbohydrate-binding proteins may not necessarily show the corresponding biological activity, andfurther selection based on biochemical studies is always required. The degree of structural mimicryrequired to generate the desired biological activity is therefore an interesting question. This reviewwill discuss recent structural studies of peptide-carbohydrate mimicry employing NMR spectroscopy,X-ray crystallography, and molecular modeling, as well as relevant biochemical data. These studiesprovide insights into the basis of mimicry at the molecular level. Comparisons with other carbohydrate-mimeticcompounds, namely proteins and glycopeptides, will be drawn. Finally, implications for the designof new therapeutic compounds will also be presented.

Development of a multi-mimotope peptide as a vaccine immunogen for infectious bursal disease virus

To explore the mimotope vaccine approach against infectious bursal disease virus (IBDV), five IBDV-specific monoclonal antibodies (mAbs) were prepared and their binding peptides were screened against a phage-displayed 12-mer peptide library. After three rounds of biopanning, 12 phages were selected for each mAbs and their specificity to IBDV was verified by sandwich and competitive inhibition ELISAs. Seven phages per mAb were sequenced and their amino acid sequences were deduced. The five representative sequences of mimotopes corresponding mAbs were determined. An artificial gene, designated 5epis (5 epitopes) and consisting of the five mimotopes arranged in tandem (F1-F7-B34-2B1-2G8) with four GGGS spacers, was chemically synthesized and cloned into a prokaryotic expression plasmid pET28b. The protein, designated r5EPIS, was efficiently expressed in Escherichia coli and showed a size of 10kDa in SDS-PAGE. The r5EPIS protein reacted with anti-IBDV mAbs and polyclonal antibodies in Western blot immunoassays. Immunization of SPF chickens with r5EPIS protein (with Freund adjuvant, 50mug per injection on day 0 and 14) evoked high levels of antibody (12,800 by ELISA/1600 by virus neutralizing assay at day 21) and protected 100% of the chickens against a challenge of 200 ELD(50) of IBDV GX8/99 strain, which sharply contrasted with the, respectively, 13.3% and 6.6% survival rate in the adjuvant group and the untreated group. The multi-mimotope protein r5EPIS promises to be a novel subunit vaccine candidate for IBDV.

Peptide Mimics of the Group B Meningococcal Capsule Induce Bactericidal and Protective Antibodies after Immunization

Neisseria meningitidis serogroup B (MenB) is a leading cause of sepsis and meningitis in children. No vaccine is available for the prevention of these infections because the group B capsular polysaccharide (CP) (MenB CP) is unable to stimulate an immune response, due to its similarity with human polysialic acid. Because the MenB CP bears both human cross-reactive and non-cross-reactive determinants, we developed immunogenic peptide mimics of the latter epitopes. Peptides were selected from phage display libraries for their ability to bind to a protective anti-MenB CP mAb. One of these peptides (designated 9M) induced marked elevations in serum bactericidal activity, but not polysialic acid cross-reacting Abs, after gene priming followed by carrier-conjugate boosting. Moreover, the occurrence of bacteremia was prevented in infant rats by administration of immune sera before MenB challenge. 9M is a promising lead candidate for the development of an effective and affordable anti-MenB vaccine.

Solution structure of R2Sn(iv)-β-N-acetyl-neuraminate (R = Me, Bu) complexes in D2O and DMSO-d6: Experimental NMR and DFT computational study

Two diorganotin(IV)-NANA complexes (NANA (1) = beta-N-acetyl-Neuraminic Acid = 5-amino-3,5-dideoxy-D-glycero-beta-D-galactononulosic acid) with formula Me(2)Sn(iv)NANA (2) and Bu(2)Sn(IV)NANA (3) were synthesized and characterized by (1)H, (13)C and (119)Sn NMR spectroscopy, both in D(2)O and DMSO-d(6) solutions. The experimental data in DMSO suggested the monosaccharide bidentate chelation via O1 carboxylate and vicinal O2 alkoxide atoms, which, in D(2)O, can be dynamically extended to a third binding site (O8 atom) of the pendant chain. Coordination at the tin atom is discussed on the basis of experimental NMR data and DFT calculation.

Antiidiotypic DNA vaccination induces serum bactericidal activity and protection against group B meningococci

No vaccine is available for preventing infections by serogroup B Neisseria meningitidis (MenB), which accounts for a major portion of meningococcal cases in developed countries, because of the poor immunogenicity of the capsular polysaccharide (CP) even after protein conjugation. We have previously induced anticapsular antibodies by immunization with a single chain variable fragment (scFv), which mimics a protective CP epitope. This surrogate antigen, however, was ineffective at inducing serum bactericidal activity, an accepted marker of protection in humans. Serum bactericidal activity was consistently achieved by immunizing mice with the scFv-encoding gene. Immunization with vectors without a secretory signal sequence before the scFv resulted in markedly higher bactericidal activity relative to those with such a sequence. The induced antibodies were capsule specific, as shown by complete inhibition of bactericidal activity by purified MenB CP and by resistance to killing of MenA or MenC. Moreover, these antibodies were predominantly of the IgG2a isotype, reflecting a T helper type 1 response. Administration of sera from scFv gene–vaccinated animals protected infant rats against MenB bacteremia. These data illustrate the potential of vaccination with genes encoding capsular mimics in providing protection against MenB and other encapsulated bacteria.

Towards an improved serogroup BNeisseria meningitidisvaccine

Meningococcal disease, presenting primarily as septicaemia and meningitis, continues to be a devastating problem around the world. Over the last century, vaccine development has been undertaken in earnest for the prevention of this disease. Polysaccharide vaccines have been available for almost 40 years, yet they are poorly immunogenic in young children who are at the highest risk. Since their introduction into some routine immunisation schedules in 1999, polysaccharide-protein conjugate vaccines for the prevention of serogroup C meningococcal infection have proven efficacious. A quadrivalent polysaccharide-protein conjugate vaccine against serogroups A, C, W135 and Y, which is being introduced in the US this year, is hoped to control disease caused by these serogroups. To date, however, the development of a universally safe, immunogenic and effective serogroup B Neisseria meningitidis vaccine has remained a challenge. This review details the many conventional vaccine strategies and the more recent genome-derived technological approaches being used in serogroup B vaccine development. The future prevention of serogroup B disease will rely on both outer membrane vesicle vaccines being used for serosubtype-specific outbreaks and new vaccines containing multiple other antigens. Investment by the pharmaceutical industry in preclinical research and development provides hope that an efficacious serogroup B meningococcal vaccine can be developed.

Anti-idiotypic antibody as a potential candidate vaccine for Neisseria meningitidis serogroup B

Sepsis and meningitis caused by Neisseria meningitidis serogroup B (NMGB) are serious diseases in infants and young adults, but no effective vaccine is available. The capsular polysaccharide (PS) of NMGB has poor immunogenicity and a structural similarity to polysialic acid (PSA) on neuronal tissue that may elicit autoantibodies. Using HmenB3, a protective and nonautoreactive monoclonal antibody (MAb) to NMGB capsular PS, we produced an anti-idiotypic MAb, Naid60, which mimics the capsular PS of NMGB. We produced an anti-anti-idiotypic MAb, MoB34, by using the immunogenic site on Naid60 responsible for inducing the anti-NMGB PS antibody response. MoB34 elicited the complement-mediated killing of representative strains of serogroup B meningococci. MoB34 did not bind to CHP-134, a neuroblastoma cell line expressing alpha(2-8) PSA, or to mouse brain cryosections at a high concentration. Naid60-keyhole limpet hemocyanin immunization inhibited the growth of live NMGB in intraperitoneally challenged mice; in contrast, three of five control mice developed bacteremia. Thus, Naid60 has an immunogenic site that elicits antibodies with bactericidal activity against NMGB and no autoimmunity to PSA. We suggest that the immunogenic region of Naid60 is a candidate for the development of a new vaccine against NMGB.

Subtle sequence differences in a tumour-associated peptide epitope translate into major changes in antigenicity

Antigenicity, the ability to bind to members of repertoire of diverse immune receptors, is a concept that is poorly characterised with respect to its defining parameters. To learn more about its makeup, we have investigated the ability of two peptides with highly related sequences, derived from the tumour-associated antigen mucin-1, to recruit in vitro members from a large naïve repertoire of synthetic human antibody fragments. One of the peptides represents the epitope that is immunodominant in mice. We now demonstrate that the other peptide, which differs from the first only by a very conservative aspartate-threonine to glutamate-serine change, is much less antigenic than the first peptide. This is so despite the fact that there is no observable difference in the tendency of the two peptides to adopt a structure in solution. Furthermore, the peptides differ in their immunodominant parts and the less antigenic peptide selects for antibody fragments targeting residues outside of the epitope considered to be immunodominant in mice. We conclude that subtle sequence changes greatly, affect antigenicity and immunodominance of epitopes in this important tumour-associated antigen.

Use of phage display to identify potential Pseudomonas aeruginosa gene products relevant to early cystic fibrosis airway infections

Pseudomonas aeruginosa airway infections are a major cause of morbidity and mortality in patients with cystic fibrosis. Treatment of established infections is difficult, even with microbiologically active agents. Thus, prevention of infection is an important goal of management. Isolates from cystic fibrosis patients appear to originate from the environment but adapt to the milieu of the airway of the cystic fibrosis patient and evolve toward a common phenotype. Identification of the antigens expressed early in infection may lead to novel targets for vaccine development. Immunogenic peptides were identified in a J404 random nonapeptide phage display library with serum from cystic fibrosis patients obtained within the first year of P. aeruginosa infection. One hundred sixty-five reactive clones were verified by plaque lift assays, and their inserts were sequenced. The sequenced nonapeptides were compared with the published sequence of strain PAO1, identifying homologies to 76 genes encoding outer membrane and secreted proteins. The majority of these were proteins involved in small-molecule transport, membrane structural proteins, and secreted factors. An in silico analysis was performed that suggested that the occurrence of multiple matches to predominantly outer membrane and secreted proteins was not attributable to random chance. Finally, gene expression array data from early isolates of P. aeruginosa from cystic fibrosis patients was compared with the results from phage display analysis. Eleven outer membrane and secreted proteins were common between the two data sets. These included genes involved in iron acquisition, antibiotic efflux, fimbrial biogenesis, and pyocin synthesis. These results demonstrate the feasibility and validity of this novel approach and suggest potential targets for future development.

A peptide mimotope of type 8 pneumococcal capsular polysaccharide induces a protective immune response in mice

Increasing antibiotic resistance and a rising patient population at risk for infection due to impaired immunity underscore the importance of vaccination against pneumococci. However, available capsular polysaccharide vaccines are often poorly immunogenic in patients at risk for pneumococcal disease. The goal of this study was to explore the potential of peptide mimotopes to function as alternative vaccine antigens to elicit a type-specific antibody response to pneumococci. We used a human monoclonal immunoglobulin A (IgA) antibody (NAD) to type 8 Streptococcus pneumoniae capsular polysaccharide (type 8 PS) to screen a phage display library, and the phage PUB1 displaying the peptide FHLPYNHNWFAL was selected after three rounds of biopanning. Inhibition studies with phage-displayed peptide or the peptide PUB1 and type 8 PS showed that PUB1 is a mimetic of type 8 PS. PUB1 conjugated to tetanus toxoid (PUB1-TT) induced a type 8 PS-specific antibody response in BALB/c mice, further defining it as a mimotope of type 8 PS. The administration of immune sera obtained from PUB1-TT-immunized mice earlier (days 14 and 21) and later (days 87 and 100) after primary and reimmunization resulted in a highly significant prolongation of the survival of naive mice after pneumococcal challenge compared to controls. The survival of PUB1-TT-immunized mice was also prolonged after pneumococcal challenge nearly 4 months after primary immunization. The efficacy of PUB1-TT-induced immune sera provides proof of principle that a mimotope-induced antibody response can protect against pneumococci and suggests that peptide mimotopes selected by type-specific human antibodies could hold promise as immunogens for pneumococci.

Protective immunization against group B meningococci using anti-idiotypic mimics of the capsular polysaccharide

Use of the serogroup B meningococcal capsular polysaccharide (MenB CP) as a vaccine is hampered by the presence of epitopes that cross-react with human polysialic acid. As non-cross-reactive, protective capsular epitopes have also been described, we set out to develop protein mimics of one of such epitopes using as a template a highly protective mAb (mAb Seam 3) raised against a chemically modified form of the MenB CP (N-Pr MenB CP). Using phage display, anti-idiotypic single-chain Ab fragments (scFvs) were obtained from spleen cells of mice immunized with the Seam 3 mAb. Two Seam 3-specific scFvs competed with N-Pr MenB CP for binding to either mAb Seam 3 or rabbit Abs present in typing sera. Moreover, in mice and rabbits the scFvs elicited the production of Abs reacting with both N-Pr MenB CP and whole meningococci, but not with human polysialic acid. These scFv-induced Ab responses were boostable and of the Th1 type, as shown by a predominance of IgG2a. In addition, passive immunization with sera from scFv-immunized animals partially protected neonatal mice from experimental infection with group B meningococci. In conclusion, we have produced anti-idiotypic scFvs that mimic a protective MenB CP epitope and may be useful in the development of an alternative group B meningococcal vaccine.

Antibodies to keyhole limpet hemocyanin cross-react with an epitope on the polysaccharide capsule of Cryptococcus neoformans and other carbohydrates: implications for vaccine development

Cryptococcus neoformans causes a life-threatening meningoencephalitis in AIDS patients. Mice immunized with a glycoconjugate vaccine composed of the glucuronoxylomannan (GXM) component of the cryptococcal capsular polysaccharide conjugated to tetanus toxoid produce Abs that can be either protective or nonprotective. Because nonprotective Abs block the efficacy of protective Abs, an effective vaccine must focus the Ab response on a protective epitope. Mice immunized with peptide mimetics of GXM conjugated to keyhole limpet hemocyanin (KLH) with glutaraldehyde developed Abs to GXM. However, control peptides P315 and P24 conjugated to KLH also elicited Abs to GXM. GXM-binding Abs from mice immunized with P315-KLH were inhibited by KLH treated with glutaraldehyde (KLH-g), but not by P315. Furthermore, KLH-g inhibited binding of GXM by serum of mice immunized with GXM-TT, indicating that glutaraldehyde treatment of KLH reveals an epitope(s) that cross-reacts with GXM. Vaccination with KLH-g or unmodified KLH elicited Abs to GXM, but did not confer protection against C. neoformans, suggesting the cross-reactive epitope on KLH was not protective. This was supported by the finding that 4H3, a nonprotective mAb, cross-reacted strongly with KLH-g. Sera from mice immunized with either native KLH or KLH-g cross-reacted with several other carbohydrate Ags, many of which have been conjugated to KLH for vaccine development. This study illustrates how mAbs can be used to determine the efficacy of potential vaccines, in addition to describing the complexity of using KLH and glutaraldehyde in the development of vaccines to carbohydrate Ags.

Induction of a protective capsular polysaccharide antibody response to a multiepitope DNA vaccine encoding a peptide mimic of meningococcal serogroup C capsular polysaccharide

Systemic infection by encapsulated organisms, such as Neisseria meningitidis, is a major cause of morbidity and mortality worldwide, especially in individuals less than 2 years of age. Antibodies directed at the capsular polysaccharide are shown to be protective against disease by inducing complement-dependent bactericidal activity. The current polysaccharide vaccine has been shown to be poorly immunogenic in high-risk groups and this is probably related to its T-independent properties. An alternative approach to eliciting a T-dependent serum immunoglobulin G (IgG) antibody response to encapsulated pathogens is DNA vaccination. We assessed the immunogenicity of a multiepitope DNA vaccine encoding a T-cell helper epitope and a peptide mimic of N. meningitidis serogroup C. The DNA construct induced a significant anti-polysaccharide antibody response that was bactericidal. Mice immunized with the DNA construct were subsequently protected against challenge with a lethal dose of N. meningitidis serogroup C.

Development of peptide mimotopes of lipooligosaccharide from nontypeable Haemophilus influenzae as vaccine candidates

Nontypeable Haemophilus influenzae (NTHi) is a common cause of otitis media in children and lower respiratory tract diseases in adults. So far there is no effective vaccine against NTHi. A major surface-exposed component of NTHi, lipooligosaccharide (LOS), is a virulence factor as well as a potential protective Ag. LOS is too toxic to be administered in humans. However, detoxified LOS is a T cell-independent small molecule and is poorly immunogenic in vivo, so we converted LOS into a nontoxic T cell-dependent Ag through the use of peptides that mimic the LOS by screening a phage-display peptide library with a rabbit Ab specific for NTHi LOS. Fifty-six phage clones were found to share LOS mimicry molecules. Among them, 22 clones were subjected to DNA sequencing, and four consensus sequences were identified as NMMRFTSQPPNN, NMMNYIMDPRTH, NMMKYISPPIFL, and NMMRFTELSTPS. Three of the four synthetic peptides showed strong binding reactivity to the rabbit anti-LOS Ab and also a mouse bactericidal monoclonal anti-LOS Ab in vitro, and elicited specific serum anti-LOS Abs in rabbits (27- to 81-fold) after conjugation with keyhole limpet hemocyanin. Passive immunization with the rabbit antisera resulted in a significantly enhanced pulmonary bacterial clearance in a mouse model. The enhanced bacterial clearance was eliminated if the rabbit serum was preabsorbed with NTHi LOS. These data indicate that the peptide mimotopes of LOS that we have identified might be potential components of peptide vaccines against NTHi.

Sequential immunization with vesicles prepared from heterologous Neisseria meningitidis strains elicits broadly protective serum antibodies to group B strains

The capsular polysaccharide of Neisseria meningitidis group B is an autoantigen, whereas noncapsular antigens are highly variable. These factors present formidable challenges for development of a broadly protective and safe group B vaccine. Mice and guinea pigs were sequentially immunized with three doses of micovesicles or outer membrane vesicles prepared from three meningococcal strains that were each antigenically heterologous with respect to the two major porin proteins, PorA and PorB, and the group capsular polysaccharide. The resulting antisera conferred passive protection against meningococcal group B bacteremia in infant rats and elicited complement-mediated bactericidal activity against genetically diverse group B strains that were either homologous or heterologous with respect to PorA of the strains used to prepare the vaccine. By using knockout strains, a portion of the bactericidal antibody was directed against the highly conserved protein, neisserial surface protein A (NspA). Further, an anti-NspA monoclonal antibody elicited by the sequential immunization was highly bactericidal against strains that were previously shown to be resistant to bacteriolysis by anti-NspA antibodies produced by immunization with recombinant NspA. Sequential immunization with heterologous vesicle preparations offers a novel approach to eliciting broadly protective immunity against N. meningitidis strains. An NspA-based vaccine prepared from protein expressed by Neisseria also may be more effective than the corresponding recombinant protein made in Escherichia coli.

Selection of mimotopes of the cell surface adhesion molecule Mel-CAM from a random pVIII-28aa phage peptide library

The cell surface adhesion molecule Mel-CAM is highly expressed in advanced primary and metastatic melanoma. Mel-CAM was first described as an integral membrane glycoprotein of malignant melanoma cells. The murine monoclonal antibody MAd18-5D7 recognizes an epitope of the extracellular domain of Mel-CAM and is able to enhance Mel-CAM mediated adhesion of melanoma cells in aggregation assays. For the characterization of peptides that antigenically mimic surface-exposed areas of Mel-CAM we screened a newly constructed random pVIII-28aa bacteriophage peptide library against MAd18-5D7. After three panning rounds a population of phages binding to MAd18-5D7 was enriched. Peptides expressed on the surface of these phages were then tested for their specificity for the antibody's antigen binding site. DNA sequences coding for two specific peptide ligands were determined. One of the deduced amino acid sequences showed similarity to a portion of the sequence of the third immunoglobulin-like extracellular domain of Mel-CAM. Both peptides blocked the interaction of MAd18-5D7 with Mel-CAM present in a MelJuSo melanoma cell line lysate. Phage displayed as well as synthetic peptides inhibited in a dose-dependent manner the binding of MAd18-5D7 to recombinant Mel-CAM in enzyme-linked immunosorbent assay experiments. No such inhibition was observed using a panel of other anti-Mel-CAM antibodies. Our results clearly indicate that these 28mer peptides are structural equivalents of the MAd18-5D7 epitope of Mel-CAM and that they will be useful tools for further in vitro and in vivo studies of Mel-CAM mediated cell-cell interaction.

Regulating the isotypic and idiotypic profile of an anti-PC antibody response: lessons from peptide mimics

Protection against microbial invasion depends not only on the host's ability to mount an immune response, but on its ability to mount the correct immune response. Whether an antibody response is protective or not depends on both the fine antigenic specificity, that may be associated with particular idiotypes and epitope binding characteristics, and the isotype, determining antibody effector function. Thus, both the variable and the constant region of the antibodies induced by a peptide mimotope must be considered when assessing the success of any immunization. Phosphorylcholine (PC), an epitope present on the cell-wall C-polysaccharide of all pneumococcal serotypes, is capable of eliciting a protective antibody response to pneumococcal infection in mice and provides an attractive model system for understanding the immune response generated by peptide mimics. In this system, both the idiotype and isotype of protective antibodies have been determined and the characteristics of the in vivo response are well described and highly reproducible. We describe here the immune response generated by two peptide mimics of PC. Mice immunized with the peptides developed antibodies binding PC and C-polysaccharide. The idiotypic profile of the response differed depending on the peptide, but never included canonical T15(+) antibodies. The isotype of the response to peptide mimics differed depending on a combination of peptide and adjuvant, and included both IgG2a and IgG2b antibodies which are not typically seen in the response to PC. Thus, peptide mimotopes may elicit anti-polysaccharide responses, but fail to elicit the idiotypes and isotypes observed in the protective response to the microbial antigen.

Characterization of oligopeptides that cross-react with carbohydrate-specific antibodies by real time kinetics, in-solution competition enzyme-linked immunosorbent assay, and immunological analyses

Phage displaying random cyclic 7-mer, and linear 7-mer and 12-mer peptides at the N terminus of the coat protein, pIII, were panned with the murine monoclonal antibody, 9-2-L379 specific for meningococcal lipo-oligosaccharide. Five cyclic peptides with two sequence motifs, six linear 7-mers, and five linear 12-mers with different sequence motifs were identified. Only phage displaying cyclic peptides were specifically captured by and were antigenic for 9-2-L379. Monoclonal antibody 9-2-L379 exhibited "apparent" binding affinities to the cyclic peptides between 11 and 184 nm, comparable with lipo-oligosaccharide. All cyclic peptides competed with the binding of 9-2-L379 to lipo-oligosaccharide with EC(50) values in the range 10-105 microm, which correlated with their apparent binding affinities. Structural modifications of the cyclic peptides eliminated their ability to bind and compete with monoclonal antibody 9-2-L379. Mice (C3H/HeN) immunized with the cyclic peptide with optimal apparent binding affinity and EC(50) of competition elicited cross-reactive antibodies to meningococcal lipo-oligosaccharide with end point dilution serum antibody titers of 3200. Cyclic peptides were converted to T-cell-dependent immunogens without disrupting these properties by C-terminal biotinylation and complexing with NeutrAvidin. The data indicate that constrained peptides can cross-react with a carbohydrate-specific antibody with greater specificity than linear peptides, and critical to this specificity is their structural conformation.

Meningococcal disease: how to prevent and how to manage

Meningococcal disease is a significant problem in the paediatric population. The diagnosis of meningococcal disease can be problematic and progression of the disease can rapidly lead to a life-threatening illness. Despite the success of antibiotic treatment, mortality rates remain high. The development of protein-polysaccharide conjugate vaccines has significantly improved the success of vaccination in reducing the incidence of meningococcal disease. However, a comprehensive vaccine conferring protection against disease-associated serogroups remains elusive. The aim of this review is to highlight recent significant improvements in the prevention and management of meningococcal disease.

Molecular mimetics of Neisseria meningitidis serogroup B polysaccharide

Strains of Neisseria meningitidis serogroup B (NmB) are an important cause of meningitis and sepsis. Efforts to develop a NmB vaccine have been hampered by poor immunogenicity of the polysaccharide capsule, which cross-reacts with host polysialic acid, and the danger of eliciting autoantibodies. To investigate the potential of molecular mimetics to circumvent these problems, we prepared murine monoclonal antibodies (mAbs) against the N-propionyl derivative (N-Pr) of NmB polysaccharide. Several mAbs were found that reacted with capsular polysaccharide epitopes, which were distinct from host polysialic acid. These mAbs also passively conferred protection against experimental bacteremia. We used these mAbs to screen novel independently folding peptide phage display libraries, and pools of combinatorial small molecules, each consisting of approximately 30 to approximately 700 small molecules of diverse composition. To date, several mimetic candidates have been identified. One is a peptide selected from a library of independently folding alphabeta peptides, and others are peptoid dimers or trimers selected from the small molecule pools. The peptoids contain an indan-type of ring system, and some of them also contain a large hydrophobic group such as oleyl amine or dehydroabietyl amine, and a positively charged group at the amino-terminus. Both the alphabeta peptide from the phage library, and the peptoids from the small molecule pools, inhibit binding of the mAbs to N-Pr NmB polysaccharide. Future studies will focus on the structure/activity relationship of these mimetics, and the development of immunogens that may be capable of eliciting anticapsular antibody without autoantibody activity.

Peptide mimotopes as surrogate antigens of carbohydrates in vaccine discovery

Carbohydrate antigens are immune targets associated with a variety of pathogens and tumor cells. Unfortunately, most carbohydrates are intrinsically T cell-independent antigens, which diminishes their efficacy as immunogens. The conversion of carbohydrate epitopes to peptide mimotopes is one means to overcome the T cell-independent nature of carbohydrate antigens because peptides have an absolute requirement for T cells. Although such conversion has great potential for the development of veterinarian and human vaccines, there are issues related to the use of peptide-based immunogens as functional surrogates. Some of these issues are fundamental, pertaining to how mimicry comes about at the molecular level, and some are application oriented, directed at elucidating important immunological mechanisms. In this article the potential and caveats of this technology regarding its application in vaccine discovery are analyzed.

Role of SA-Le(a) and E-selectin in metastasis assessed with peptide antagonist

E-selectin ligand Sialyl-Lewis a (SA-Le(a)) carbohydrate is expressed on many carcinomas. Peptide mimicking SA-Le(a) (DLWDWVVGKPAG) was previously selected from a recombinant library by screening with monoclonal antibody (MAb) NS19-9. In this study, the residues critical for interaction with the NS19-9 were mapped using peptide array generated by substitution of various amino acid residues. The replacement of Trp 5 with Phe resulted in a change of peptide's secondary structure and increased binding with MAb and E-selectin, suggesting improved carbohydrate mimicry. Colonization of tumor cells expressing SA-Le(a) was blocked by the peptide and was completely abolished in E-selectin knock out mice. The data suggest the critical role of carbohydrate antigens and E-selectin in metastasis and that peptides mimicking carbohydrate antigens can function as antagonists of this process.

A synthetic peptide with estrogen-like activity derived from a phage-display peptide library

We describe a novel approach to develop peptides with estrogen like activity using a monoclonal antibody specific to estradiol (mAb E2-15) for the affinity selection of phage displayed peptides from a combinatorial peptide library. Based on the sequences of the selected phage, we synthesized a 15-mer linear peptide LPALDPTKRWFFETK which was derivatized to a 23 mer cyclic peptide CAELPALDPTKRWFFETKPPPPC. Both peptides displayed estrogen-like activity according to the following criteria:(i) in inhibiting the binding of [3H]estradiol to mAb E2-15 and to estrogen receptor (ER)alpha; (ii) in inducing transcriptional activity in MCF7 human breast cancer cells transfected with an estrogen receptor element luciferase construct and (iii) in causing an increase in creatine kinase specific activity in rat tissues in vivo. This approach can be employed to design peptide mimetic for other hormones as well.

Novel vaccine strategies to T-independent antigens

T cell independent antigens do not require T cell help to induce an immune response, and are characterized by a lack of immunologic memory. These antigens can be divided into two classes, TI-1 or TI-2. TI-1 antigens, such as bacterial lipopolysaccharide, are potent B-cell mitogens, capable of non-specific, polyclonal activation of B cells. In contrast, TI-2 antigens can only activate mature B cells and consist of highly repetitive structures, such as capsular polysaccharides (CPS) from bacteria. Many vaccines currently in use consist of purified capsular polysaccharides from pathogenic bacteria such as Streptococcus pneumoniae and Neisseria meningitidis. These vaccines are efficacious in immune-competent adults, however, due to their TI-2 nature, are not effective in children <2 years of age. Converting polysaccharides into T cell dependent (TD) antigens, allows children, <2, to produce an effective immune response. This review focuses on various strategies used to convert the immune response to polysaccharide antigens from TI-2 to a TD response. Conjugate vaccines, anti-idiotypic antibodies, phage display library technology and DNA vaccines are discussed.

Activity and cross-reactivity of antibodies induced in mice by immunization with a group B meningococcal conjugate

The capsular polysaccharide of group B Neisseria meningitidis is composed of a linear homopolymer of alpha(2-8) N-acetyl neuraminic acid or polysialic acid (PSA) that is also carried by isoforms of the mammalian neural cell adhesion molecule (NCAM), which is especially expressed on brain cells during development. Here we analyzed the ability of antibodies induced by the candidate vaccine N-propionyl polysaccharide tetanus toxoid conjugate to recognize PSA-NCAM. We hyperimmunized mice to produce a pool of antisera and a series of immunoglobulin G monoclonal antibodies and evaluated their self-reactivity profile by using a battery of tests (immunoprecipitation, immunoblotting, and immunofluorescence detection on live cells and human tissue sections) chosen for their sensitivity and specificity to detect PSA-NCAM in various environments. We also searched for the effects of the vaccine-induced antibodies in two functional assays involving cell lysis or cell migration. Although they were highly bactericidal, all the antibodies tested showed very low or no recognition of PSA-NCAM, in contrast to PSA-specific monoclonal antibodies used as controls. Different patterns of cross-reactions were revealed by the tests used, likely due to affinity and specificity differences among the populations of induced antibodies. Furthermore, neither cell lysis nor perturbation of migration was observed in the presence of the tested antibodies. Importantly, we showed that whereas enzymatic removal of PSA groups from the surfaces of live cells perturbed their migration, blocking them with PSA-specific antibodies was not functionally detrimental. Taken together, our data indicated that this candidate vaccine induced antibodies that could not demonstrate an immunopathologic effect.

Immunological characterization of peptide mimetics of carbohydrate antigens in vaccine design strategies

Targeting antigens which cannot be readily addressed by genetic vectors is a major challenge in vaccine design. The inter-conversion of carbohydrate antigens into peptide mimetic forms provides a means to broaden the immune response to carbohydrate antigens. Peptides that mimic carbohydrate antigens offer new possibilities to augment immune responses to such antigens that include inducing carbohydrate reactive T-cell responses. Peptide mimeotopes can be formulated in a variety of ways that include multiple antigen peptides (MAP) and as DNA vaccines that prime for different antibody isotypes. On the immunological side we observe that: (i) depending on the immunogen formulation peptide mimetics can be processed by either CD5+ or CD5-B cells; (ii) peptide mimeotope immunization can induce cross-reactive responses to multiple carbohydrate forms; (iii) priming with peptide mimeotopes can enhance carbohydrate immune responses upon boosting and (iv) immunization with peptide mimeotopes can induce carbohydrate reactive T cells.

Directing the immune response to carbohydrate antigens

Peptide mimetics may substitute for carbohydrate antigens in vaccine design applications. At present, the structural and immunological aspects of antigenic mimicry, which translate into immunologic mimicry, as well as the functional correlates of each, are unknown. In contrast to screening peptide display libraries, we demonstrate the feasibility of a structure-assisted vaccine design approach to identify functional mimeotopes. By using concanavalin A (ConA), as a recognition template, peptide mimetics reactive with ConA were identified. Designed peptides were observed to compete with synthetic carbohydrate probes for ConA binding, as demonstrated by enzyme-linked immunosorbent assay and isothermal titration calorimetry (ITC) analysis. ITC measurements indicate that a multivalent form of one particular mimetic binds to ConA with similar affinity as does trimannoside. Splenocytes from mimeotope-immunized mice display a peptide-specific cellular response, confirming a T-cell-dependent nature for the mimetic. As ConA binds to the Envelope protein of the human immunodeficiency virus, type 1 (HIV-1), we observed that mimeotope-induced serum also binds to HIV-1-infected cells, as assessed by flow cytometry, and could neutralize T-cell line adapted HIV-1 isolates in vitro, albeit at low titers. These studies emphasize that mimicry is based more upon functional rather than structural determinants that regulate mimeotope-induced T-dependent antibody responses to polysaccharide and emphasize that rational approaches can be employed to develop further vaccine candidates.

Monoclonal antibodies specific for Neisseria meningitidis group B polysaccharide and their peptide mimotopes

From five mice immunized with Escherichia coli K1 bacteria, we produced 12 immunoglobulin M hybridomas secreting monoclonal antibodies (MAbs) that bind to Neisseria meningitidis group B (NMGB). The 12 MAbs also bound the capsular polysaccharide (PS) of E. coli K1 [which, like NMGB, is alpha(2-8)-linked polysialic acid (PSA)] and bound to EV36, a nonpathogenic E. coli K-12 strain producing alpha(2-8) PSA. Except for HmenB5, which cross-reacted with N. meningitidis group C, none of the MAbs bound to N. meningitidis groups A, C, and Y. Of the 12 MAbs, 6 were autoantibodies as defined by binding to CHP-134, a neuroblastoma cell line expressing short-chain alpha(2-8) PSA; five of these MAbs killed NMGB in the presence of rabbit complement, and two also killed NMGB with human complement. The other six MAbs, however, were nonautoreactive; all killed NMGB with rabbit complement, and five killed NMGB with human complement. To obtain peptide mimotopes of NMGB PS, four of the nonautoreactive MAbs (HmenB2, HmenB3, HmenB13, and HmenB14) were used to screen two types of phage libraries, one with a linear peptide of 7 amino acids and the other with a circular peptide of 7 amino acids inserted between two linked cysteines. We obtained 86 phage clones that bound to the screening MAb in the absence but not in the presence of E. coli K1 PSA in solution. The clones contained 31 linear and 4 circular mimotopes expressing unique sequences. These mimotopes nonrandomly expressed amino acids and were different from previously described mimotopes for NMGB PS. The new mimotopes may be useful in producing a vaccine(s) capable of eliciting anti-NMGB antibodies not reactive with neuronal tissue.

The mimicry of human glycolipids and glycosphingolipids by the lipooligosaccharides of pathogenic neisseria and haemophilus

It has been known for many years that bacteria can induce autoimmune responses in humans resulting in serious disease. Recent work has shown that a number of bacteria that colonize human mucosal surfaces exclusively express antigens on their surfaces which are molecular mimics of glycosphingolipids found on human cells. These structures are important in the pathogenesis of Neisseria and Haemophilus species for both immune evasion and in the adherence and invasion of human cells. There is no evidence that colonization or infections by these bacterial species is associated with autoimmune disease.

Biotechnological applications of phage and cell display

In recent years, the use of surface-display vectors for displaying polypeptides on the surface of bacteriophage and bacteria, combined with in vitro selection technologies, has transformed the way in which we generate and manipulate ligands, such as enzymes, antibodies and peptides. Phage display is based on expressing recombinant proteins or peptides fused to a phage coat protein. Bacterial display is based on expressing recombinant proteins fused to sorting signals that direct their incorporation on the cell surface. In both systems, the genetic information encoding for the displayed molecule is physically linked to its product via the displaying particle. Using these two complementary technologies, we are now able to design repertoires of ligands from scratch and use the power of affinity selection to select those ligands having the desired (biological) properties from a large excess of irrelevant ones. With phage display, tailor-made proteins (fused peptides, antibodies, enzymes, DNA-binding proteins) may be synthesized and selected to acquire the desired catalytic properties or affinity of binding and specificity for in vitro and in vivo diagnosis, for immunotherapy of human disease or for biocatalysis. Bacterial surface display has found a range of applications in the expression of various antigenic determinants, heterologous enzymes, single-chain antibodies, and combinatorial peptide libraries. This review explains the basis of phage and bacterial surface display and discusses the contributions made by these two leading technologies to biotechnological applications. This review focuses mainly on three areas where phage and cell display have had the greatest impact, namely, antibody engineering, enzyme technology and vaccine development.

A cryptococcal capsular polysaccharide mimotope prolongs the survival of mice with Cryptococcus neoformans infection

Defined Abs to the Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM) have been shown to be protective against experimental cryptococcosis. This suggests that if a vaccine could induce similar Abs it might protect against infection. However, the potential use of a GXM-based vaccine has been limited by evidence that GXM is a poor immunogen that can induce nonprotective and deleterious, as well as protective, Abs, and that the nature of GXM oligosaccharide epitopes that can elicit a protective response is unknown. In this study, we investigated whether a peptide surrogate for a GXM epitope could induce an Ab response to GXM in mice. The immunogenicity of peptide-protein conjugates produced by linking a peptide mimetic of GXM, P13, to either BSA, P13-BSA, or tetanus toxoid, P13-tetanus toxoid, was examined in BALB/c and CBA/n mice that received four s.c. injections of the conjugates at 14- to 30-day intervals. All mice immunized with conjugate produced IgM and IgG to P13 and GXM. Challenge of conjugate-immunized mice with C. neoformans revealed longer survival and lower serum GXM levels than control mice. These results indicate that 1) P13 is a GXM mimotope and 2) that it induced a protective response against C. neoformans in mice. P13 is the first reported mimotope of a C. neoformans Ag. Therefore, the P13 conjugates are vaccine candidates for C. neoformans and their efficacy in this study suggests that peptide mimotopes selected by protective Abs deserve further consideration as vaccine candidates for encapsulated pathogens.

Peptide mimic of phosphorylcholine, a dominant epitope found on Streptococcus pneumoniae

Even in the age of antibiotics, Streptococcus pneumoniae causes significant morbidity, especially in the young, the elderly, and the immunocompromised. While a carbohydrate-based vaccine exists, it is poorly immunogenic in the at-risk populations. In mice, antibodies directed against phosphorylcholine (PC), an epitope present on the cell wall C polysaccharide of all pneumococcal serotypes, protect against infection. However, PC itself is a poor vaccine candidate. We report here peptide mimics of PC based on the anti-idiotypic interaction of T15 anti-PC antibodies. T15 antibodies, the dominant and protective idiotype induced in mice by PC immunization, self-associate via a 24-amino-acid region in the PC binding site (ASRNKANDYTTEYSASVKGRFIVS; peptide 1). Peptide 1 has been shown to bind in the PC binding site. We demonstrated that amino acid sequences derived from peptide 1 starting at amino acid 9, 11, or 13 inhibit PC binding. Therefore, we immunized mice with bovine serum albumin (BSA) conjugates of peptide 1 or either of two selected 12-mers. The 12-mer peptides were not immunogenic. Mice immunized with peptide 1-BSA developed an anti-PC response consisting mainly immunoglobulin G1 and expressed the T15 heavy chain. Nonetheless, neither BALB/c nor CBA/N mice were protected from lethal pneumococcal infections by immunization with peptide 1-BSA. Preliminary data suggest that peptide 1-BSA is not able to elicit the canonical T15 light chain, explaining the absence of protection. This idiotype-derived mimotope of PC is a useful tool for understanding immunologic cross-reactivity and learning to design T-cell-dependent vaccines for S. pneumoniae.

Peptide mimics elicit antibody responses against the outer-membrane lipooligosaccharide of group B neisseria meningitidis

As an alternative approach towards the development of a meningococcal vaccine, the potential of peptide mimics of lipooligosaccharide (LOS) to elicit cross-reactive immune responses against LOS was investigated. The heptapeptides SMYGSYN and APARQLP were identified by enrichment from a coliphage display library with a LOS-specific monoclonal antibody. Mice immunised with these peptides conjugated to diphtheria toxoid elicited a total IgG response to LOS with geometric mean titres 2-4 times higher compared with non-immunised controls. There was an increase in LOS-specific IgG1 immunoglobulin, whereas specific IgG2a and IgG3 decreased slightly in response to immunisation. The data demonstrated that peptide mimics can elicit immune responses against meningococcal LOS.