The assembly and immunological properties of non-linear synthetic immunogens containing T-cell and B-cell determinants

Sequential Immunizations with Influenza Neuraminidase Protein Followed by Peptide Nanoclusters Induce Heterologous Protection

Enhancing cross-protections against diverse influenza viruses is desired for influenza vaccinations. Neuraminidase (NA)-specific antibody responses have been found to independently correlate with a broader influenza protection spectrum. Here, we report a sequential immunization regimen that includes priming with NA protein followed by boosting with peptide nanoclusters, with which targeted enhancement of antibody responses in BALB/c mice to certain cross-protective B-cell epitopes of NA was achieved. The nanoclusters were fabricated via desolvation with absolute ethanol and were only composed of composite peptides. Unlike KLH conjugates, peptide nanoclusters would not induce influenza-unrelated immunity. We found that the incorporation of a hemagglutinin peptide of H2-d class II restriction into the composite peptides could be beneficial in enhancing the NA peptide-specific antibody response. Of note, boosters with N2 peptide nanoclusters induced stronger serum cross-reactivities to heterologous N2 and even heterosubtypic N7 and N9 than triple immunizations with the prototype recombinant tetrameric (rt) N2. The mouse challenge experiments with HK68 H3N2 also demonstrated the strong effectiveness of the peptide nanocluster boosters in conferring heterologous protection.

S. Typhi derived vaccines and a proposal for outer membrane vesicles (OMVs) as potential vaccine for typhoid fever

Typhoid fever is a serious systemic infection caused by Salmonella Typhi (S. Typhi), spread by the feco-oral route and closely associated with poor food hygiene and inadequate sanitation. Nearly 93% of S. Typhi strains have acquired antibiotic resistance against most antibiotics. Vaccination is the only promising way to prevent typhoid fever. This review covers the nature and composition of S. Typhi, pathogenecity and mode of infection, epidemiology, and nature of drug resistance. Several components (Vi-polysaccharides, O-antigens, flagellar antigens, full length OMPs, and short peptides from OMPs) of S. Typhi have been utilized for vaccine design for protection against typhoid fever. Vaccine delivery systems also contribute to efficacy of the vaccines. In this study, we propose to develop S. Typhi derived OMVs as vaccine for protection against typhoid fevers.

Geometry of a TLR2-Agonist-Based Adjuvant Can Affect the Resulting Antigen-Specific Immune Response

Targeted delivery of otherwise nonimmunogenic antigens to Toll-like receptors (TLRs) expressed on dendritic cells (DCs) has proven to be an effective means of improving immunogenicity. For this purpose, we have used a branched cationic lipopeptide, R₄Pam₂Cys, which is an agonist for TLR2 and enables electrostatic association with antigen for this purpose. Here, we compare the immunological properties of ovalbumin formulated with different geometrical configurations of R₄Pam₂Cys. Our results demonstrate that notwithstanding the presence of the same adjuvant, branched forms of R₄Pam₂Cys are more effective at inducing immune responses than are linear geometries. CD8⁺ T-cell-mediated responses are particularly improved, resulting in significantly higher levels of antigen-specific cytokine secretion and cytolysis of antigen-bearing target cells in vivo. The results correlate with the ability of branched R₄Pam₂Cys conformations to encourage higher levels of DC maturation and facilitate superior antigen uptake, leading to increased production of proinflammatory cytokines. These differences are not attributable to particle size because both branched and linear lipopeptides associate with antigen-forming complexes of similar size, but rather the ability of branched lipopeptides to induce more efficient TLR2-mediated cell signaling. Branched lipopeptides are also more resistant to trypsin-mediated proteolysis, suggesting greater stability than their linear counterparts. The branched lipopeptide facilitates presentation of antigen more efficiently to CD8⁺ T cells, resulting in rapid cell division and upregulation of early cell surface activation markers. These results as well as cognate recognition of Pam₂Cys by TLR2 indicate that the adjuvant's efficiency is also dependent on its geometry.

Activation of monocytic cells by immunostimulatory lipids conjugated to peptide antigens

Bacterial derived lipoproteins constitute potent macrophage activators in vivo and are effective stimuli, enhancing the immune response especially with respect to low or non-immunogenic compounds. In the present study we have prepared branched lipopeptide constructs in which different (B- and T-cell) epitopes of Herpes simplex virus type 1, derived from glycoproteins B (gB) and D (gD), are linked to a synthetic lipid core. The ability of the lipid core peptide (LCP) constructs (LCP-gB and LCP-gD) to induce cytokine expression and activate the mitogen-activated protein kinase cascade has been evaluated and compared with the behaviour of the isolated epitopes and the lipid core. In this respect, the use of LCP technology coupled with the use of three different gB or gD peptide epitopes in the same branched constructs could represent an interesting approach in order to obtain efficient delivery systems in the development of a synthetic multiepitopic vaccine for the prevention of viral infections.

Antitumor activity of a self-adjuvanting glyco-lipopeptide vaccine bearing B cell, CD4+ and CD8+ T cell epitopes

Molecularly defined synthetic vaccines capable of inducing both antibodies and cellular anti-tumor immune responses, in a manner compatible with human delivery, are limited. Few molecules achieve this target without utilizing external immuno-adjuvants. In this study, we explored a self-adjuvanting glyco-lipopeptide (GLP) as a platform for cancer vaccines using as a model MO5, an OVA-expressing mouse B16 melanoma. A prototype B and T cell epitope-based GLP molecule was constructed by synthesizing a chimeric peptide made of a CD8(+) T cell epitope, from ovalbumin (OVA(257-264)) and an universal CD4(+) T helper (Th) epitope (PADRE). The resulting CTL-Th peptide backbones was coupled to a carbohydrate B cell epitope based on a regioselectively addressable functionalized templates (RAFT), made of four alpha-GalNAc molecules at C-terminal. The N terminus of the resulting glycopeptides (GP) was then linked to a palmitic acid moiety (PAM), obviating the need for potentially toxic external immuno-adjuvants. The final prototype OVA-GLP molecule, delivered in adjuvant-free PBS, in mice induced: (1) robust RAFT-specific IgG/IgM that recognized tumor cell lines; (2) local and systemic OVA(257-264)-specific IFN-gamma producing CD8(+) T cells; (3) PADRE-specific CD4(+) T cells; (4) OVA-GLP vaccination elicited a reduction of tumor size in mice inoculated with syngeneic murine MO5 carcinoma cells and a protection from lethal carcinoma cell challenge; (5) finally, OVA-GLP immunization significantly inhibited the growth of pre-established MO5 tumors. Our results suggest self-adjuvanting glyco-lipopeptide molecules as a platform for B Cell, CD4(+), and CD8(+) T cell epitopes-based immunotherapeutic cancer vaccines.

Peptide-based vaccines for cancer: realizing their potential

Advances in the engineering of peptides, adjuvants and delivery systems have renewed the enthusiasm for peptide-based vaccination regimens in the setting of cancer, and there are a variety of clinical trials being conducted by pharmaceutical companies based on the use of peptides. The challenges to successful cancer immunotherapy are common to all immunotherapeutic strategies and not unique to peptide-based vaccination regimens. This review will describe the advances in the identification, design and delivery of peptides, the challenges to successful immunotherapy and will discuss potential options for the future.

Dendritic cell acquisition of epitope cargo mediated by simple cationic peptide structures

In this study we evaluate the uptake by murine dendritic cells (DCs) of different synthetic, branched cationic peptide structures with a view to facilitating peptide epitope delivery. The level of cell uptake by fluorescenated peptides was measured by flow cytometry following quenching of extracellular fluorescence with trypan blue. Branched peptides containing either N-terminal arginine or N-terminal lysine residues were able to mediate cell entry but the peptide containing four arginine residues in a branching configuration (R4) was found to be superior not only to other branched peptides in translocating to the cell interior and also to a peptide containing four arginine residues arranged linearly. Fluorescenated R4 was found to be localized within intracellular vesicle-like compartments as well as being distributed throughout the cell cytoplasm. Uptake of R4 utilized an energy-dependent process that appeared to involve phosphatidylinositol-3-kinase and could induce intermediate levels of DC maturation. R4 when conjugated to a T-helper cell and CTL epitope construct was able to induce antigen-specific CD8+ T-cell mediated immune responses in mice when administered in adjuvant as were DCs that were pulsed with this construct and then matured with LPS. Fluorescenated R4 was also found to translocate into the interior of other cell types indicating that it may be useful for the delivery of peptide cargo into other specialized cells.

Generation of monoclonal antibodies of desired specificity using chimeric polyomavirus-derived virus-like particles

Foreign protein sequences presented on hamster polyomavirus (HaPyV) major capsid protein VP1-derived virus-like particles (VLPs) have been demonstrated to be highly immunogenic. The current study was aimed to evaluate VP1-derived chimeric VLPs as tools for hybridoma technology to generate monoclonal antibodies (mAbs) of desired specificity. Chimeric VLPs containing inserts of different size and origin were used as immunogens. Chimeric VLPs carrying a 9 amino acid (aa)-long cytotoxic T-cell epitope (STAPPVHNV) of human mucin 1 (MUC1) elicited a strong epitope-specific humoral immune response in mice and promoted the production of MUC1-specific mAbs. From a total of seven mAbs of IgG isotype generated against the chimeric VLPs, two mAbs were directed against the MUC1 epitope and five mAbs against the VP1-carrier. Two out of five anti-VP1 mAbs recognized epitopes located at the previously defined insertion site #2 (aa 223/224), which confirms its surface-exposed localization. Chimeric VLPs carrying a 120-aa long sequence of Puumala hantavirus (PUUV) nucleocapsid protein (NP) promoted the generation of five mAbs of IgG isotype specific to PUUV NP. All mAbs recognized the full-length NP of different PUUV strains. In contrast, no VP1-specific mAbs were obtained. The ability of chimeric VLPs to activate antigen-presenting cells was evaluated by studying the uptake of chimeric VLPs by murine spleen cell-derived dendritic cells (DCs). Efficient uptake of VLPs and activation of murine DCs were demonstrated, which may represent the basis of the strong immunogenicity of chimeric VLPs. In conclusion, chimeric VLPs effectively stimulated the production of IgG antibodies specific for foreign epitopes presented at surface-exposed regions. Thus, chimeric HaPyV VP1-derived VLPs represent efficient immunogens for hybridoma technology and provide a promising alternative to chemical coupling of synthetic peptides to carrier proteins.

Plasmodium falciparum merozoite surface protein 6 is a dimorphic antigen

Merozoite surface protein 1 (MSP1) is a highly polymorphic Plasmodium falciparum merozoite surface protein implicated in the invasion of human erythrocytes during the asexual cycle. It forms a complex with MSP6 and MSP7 on the merozoite surface, and this complex is released from the parasite around the time of erythrocyte invasion. MSP1 and many other merozoite surface proteins contain dimorphic elements in their protein structures, and here we show that MSP6 is also dimorphic. The sequences of eight MSP6 genes indicate that the alleles of each dimorphic form of MSP6 are highly conserved. The smaller 3D7-type MSP6 alleles are detected in parasites from all malarious regions of the world, whereas K1-type MSP6 alleles have only been detected in parasites from mainland Southeast Asia. Cleavage of MSP6, which produces the p36 fragment in 3D7-type MSP6 and associates with MSP1, also occurs in K1-type MSP6 but at a different site in the protein. Anti-3D7 MSP6 antibodies weakly inhibited erythrocyte invasion by homologous 3D7 merozoites but did not inhibit a parasite line expressing the K1-type MSP6 allele. Antibodies from hyperimmune individuals affinity purified on an MSP3 peptide cross-reacted with MSP6; therefore, MSP6 may also be a target of antibody-dependent cellular inhibition.

DCs as targets for vaccine design

The increasingly stringent requirements laid down by regulatory authorities have brought to an end the largely empirical design of vaccines. Vaccines must now be designed rationally, in order that appropriate immune responses are elicited with few or no side effects. The DC plays a pivotal role in determining the type of immune response that ensues following exposure of the host to an Ag. In this review, we identify some of the features and properties of DCs, and how these properties can be exploited in the design of smart vaccines.

Potential of lipid core peptide technology as a novel self-adjuvanting vaccine delivery system for multiple different synthetic peptide immunogens

This study demonstrates the effectiveness of a novel self-adjuvanting vaccine delivery system for multiple different synthetic peptide immunogens by use of lipid core peptide (LCP) technology. An LCP formulation incorporating two different protective epitopes of the surface antiphagocytic M protein of group A streptococci (GAS)--the causative agents of rheumatic fever and subsequent rheumatic heart disease--was tested in a murine parenteral immunization and GAS challenge model. Mice were immunized with the LCP-GAS formulation, which contains an M protein amino-terminal type-specific peptide sequence (8830) in combination with a conserved non-host-cross-reactive carboxy-terminal C-region peptide sequence (J8) of the M protein. Our data demonstrated immunogenicity of the LCP-8830-J8 formulation in B10.BR mice when coadministered in complete Freund's adjuvant and in the absence of a conventional adjuvant. In both cases, immunization led to induction of high-titer GAS peptide-specific serum immunoglobulin G antibody responses and induction of highly opsonic antibodies that did not cross-react with human heart tissue proteins. Moreover, mice were completely protected from GAS infection when immunized with LCP-8830-J8 in the presence or absence of a conventional adjuvant. Mice were not protected, however, following immunization with an LCP formulation containing a control peptide from a Schistosoma sp. These data support the potential of LCP technology in the development of novel self-adjuvanting multi-antigen component vaccines and point to the potential application of this system in the development of human vaccines against infectious diseases.

Dissecting the role of peptides in the immune response: theory, practice and the application to vaccine design

Analytical biochemistry and synthetic peptide based chemistry have helped to reveal the pivotal role that peptides play in determining the specificity, magnitude and quality of both humoral (antibody) and cellular (cytotoxic and helper T cell) immune responses. In addition, peptide based technologies are now at the forefront of vaccine design and medical diagnostics. The chemical technologies used to assemble peptides into immunogenic structures have made great strides over the past decade and assembly of highly pure peptides which can be incorporated into high molecular weight species, multimeric and even branched structures together with non-peptidic material is now routine. These structures have a wide range of applications in designer vaccines and diagnostic reagents. Thus the tools of the peptide chemist are exquisitely placed to answer questions about immune recognition and along the way to provide us with new and improved vaccines and diagnostics.

Reactivity and isotype profiling of monoclonal antibodies using multiple antigenic peptides

The characterisation of monoclonal antibodies (MAbs) is essential for the development of assay systems particularly where antigens have been developed using synthetic peptides. Indeed some peptide-carrier conjugates fail to induce immune responses and may not generate antibodies that bind to native protein. As an alternative to peptide-carrier conjugates, multiple antigenic peptides (MAPs) have been used for immunization strategies, but with little regard to the characteristics of the MAbs produced. In this study, we used 3 MAPs of Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) to immunise BALB/c mice. Overall, the polyclonal antibody responses from tail bleeds showed that MAPs evoked B-cell responses. However, on screening 144 hybridomas, 24 MAb supernatants exhibited weak to moderate reactivity in enzyme-linked immunosorbant assay (ELISA) and against cell cytospin preparations (B95.8 and AG876 LCL), respectively. Isotype profiling of hybridoma supernatants also showed that 11 out of 24 were IgM. Further characterization of 6 MAbs in Western blotting showed reactivity to recombinant LMP1 and only one MAb (B28D) showed weak reactivity to the malignant cells (Hodgkin/Reed-Sternberg; HRS cells) of an EBV+ Hodgkin's lymphoma using paraffin-embedded tissue. It is probable that these MAPs failed to augment T-cell help and contributed to the production of low affinity (IgM) antibodies. These observations may be of importance to future immunization strategies, where MAPs are used in the production of monoclonal reagents.

Synthetic peptide epitope-based polymers: controlling size and determining the efficiency of epitope incorporation

The assembly of synthetic peptide-based vaccines that incorporate multiple epitopes is a major goal of vaccine development, because such vaccines will potentially allow the immunization of outbred populations against a number of different pathogens. We have shown that free radical-induced polymerization of individual peptide epitopes results in the incorporation of multiple copies of the same or different epitopes into high molecular weight immunogens (O'Brien-Simpson, N.M., Ede, N.J., Brown, L.E., Swan, J. & Jackson, D.C. (1997) Polymerization of unprotected synthetic peptides: a view toward synthetic peptide vaccines. J. Am. Chem. Soc.119, 1183-1188; Jackson, D.C., O'Brien-Simpson, N., Ede, N.J. & Brown, L.E. (1997) Free radical induced polymerization of synthetic peptides into polymeric immunogens. Vaccine 15, 1697-1705). The ability to control the size of these polymers, to determine the physical and chemical properties of the backbone material and also to know the extent to which individual peptide epitopes are incorporated are important manufacturing considerations and form the subject of this study. We show here that the polymerization process is highly efficient with at least 70% of peptides incorporated into the resulting polymer, that acrylamide and acryloylated amino acids can be used as comonomers with peptide epitopes in the polymerization reaction and that the choice of the comonomer can influence the properties of the resulting polymer. We also show that the size of chain growth polymers is restricted in the presence of chain transfer agents, that the resulting polymer size can be predicted and that there is little or no difference in the immunogenicity of polymers that range in apparent molecular size between 18 kDa and 335 kDa. The successful polymerization of peptide epitopes with an acryloyl-amino acid creates the potential for introducing different physical and chemical properties into artificial protein immunogens.

Identification of canine helper T-cell epitopes from the fusion protein of canine distemper virus

The fusion protein of canine distemper virus (CDV-F), a 662 amino-acid envelope protein, was used as the target molecule for identification of canine T helper (Th) epitopes. A library of 94 peptides, each 17 residues in length overlapping by 10 residues and covering the entire sequence of CDV-F, was screened using a lymphocyte proliferation assay with peripheral blood mononuclear cells (PBMC) obtained from dogs inoculated with canine distemper virus (CDV) vaccine. Initially we observed low and inconsistent proliferation of PBMC in response to these peptides, even when using cells obtained from dogs that had received multiple doses of CDV. Subsequently, the use of expanded cell populations derived by in vitro stimulation of canine PBMC with pools of peptides allowed the identification of a number of putative canine Th-epitopes within the protein sequence of CDV-F. There were two major clusters of Th-epitopes identified close to the cleavage site of the F0 fusion protein, while some others were scattered in both the F1 and F2 fragments of the protein. Some of these peptides, in particular peptide 35 (p35), were stimulatory in dogs of different breeds and ages. The identification of such promiscuous canine Th-epitopes encouraged us to assemble p35 in tandem with luteinising hormone releasing hormone (LHRH) a 10 amino-acid residue synthetic peptide representing a B-cell epitope which alone induces no antibody in dogs. The totally synthetic immunogen was able to induce the production of very high titres of antibodies against LHRH in all dogs tested. These results indicate that p35 could be an ideal candidate for use as a Th-epitope for use in outbred dogs.

Assembly of synthetic peptide vaccines by chemoselective ligation of epitopes: influence of different chemical linkages and epitope orientations on biological activity

In this paper, we describe the assembly of synthetic peptide vaccines composed of a T helper cell epitope and a B cell epitope that were synthesized separately and then attached using three different chemoselective ligation methods: oxime bond formation, thioether bond formation and disulfide bond formation. The resulting vaccines were tested in animals to investigate their efficacy. We found that thioether bond formation gave the highest yield of material and that the chemistry involved did not adversely affect immunogenicity and biological activity of the peptide vaccine. Ligation of epitopes by oxime bond formation did not diminish biological activity either, but the yields of peptide vaccine were lower than when thioether bond formation was used. The vaccines in which a disulfide bond was used to attach the two epitopes resulted in the lowest yield and produced vaccines that also generated a weaker immune response with sub-optimal biological activity. Connecting the T helper epitope via its N-terminus or its C-terminus to the N-terminus of the B cell epitope had little influence on resulting immunogenicity and biological activity.

Diepitopic construct of functionally and epitopically complementary peptides enhances immunogenicity, reactivity with glucosyltransferase, and protection from dental caries

Coimmunization with peptide constructs from catalytic (CAT) and glucan-binding (GLU) domains of glucosyltransferase (GTF) of mutans streptococci has resulted in enhanced levels of antibody to the CAT construct and to GTF. We designed and synthesized a diepitopic construct (CAT-GLU) containing two copies of both CAT (B epitope only) and GLU (B and T epitope) peptides. The immunogenicity of this diepitopic construct was compared with that of individual CAT and GLU constructs by immunizing groups of Sprague-Dawley rats subcutaneously in the salivary gland vicinity with the CAT-GLU, CAT, or GLU construct or by treating rats by sham immunization. Levels of serum immunoglobulin G (IgG) antibody to GTF or CAT in the CAT-GLU group were significantly greater than in GLU- or CAT-immunized groups. Immunization with CAT-GLU was compared to coimmunization with a mixture of CAT and GLU in a second rodent experiment under a similar protocol. CAT-GLU immunization resulted in serum IgG and salivary IgA responses to GTF and CAT which were greater than after coimmunization. Immunization with the diepitopic construct and communization with CAT and GLU constructs showed proliferation of T lymphocytes to GTF. Immunization with either the CAT or GLU construct has been shown to elicit significant protection in a rodent dental caries model. Similarly in this study, the enhanced response to GTF after immunization with the CAT-GLU construct resulted in protective effects on dental caries. Therefore, the CAT-GLU diepitopic construct can be a potentially important antigen for a caries vaccine, giving rise to greater immune response than after immunization with CAT, GLU, or a mixture of the two.

Differential effect of CD8(+) and CD8(-) dendritic cells in the stimulation of secondary CD4(+) T cells

Dendritic cells (DC), in their role in initiation of the adaptive immune response, have been extensively studied for their capacity to interact and stimulate naive T cells. Subsets of mature murine DC isolated directly from the spleen have been shown to differ in their ability to induce proliferative responses in both primary CD4(+) and primary CD8(+) T cells; the myeloid-related CD8alpha(-) DC induce a more intense or prolonged proliferation of naive T cells than do the lymphoid-related DC bearing CD8alpha despite similar expression of MHC and co-stimulatory molecules. Here we examine the interaction of these DC subpopulations with T cells already in the activated or memory state which are known to have greater sensitivity to antigen stimulation and bear receptors with increased capacity for signal transduction. We show that influenza virus-specific CD4(+) T cell clones and splenic T cells from peptide-primed animals proliferated in response to antigen presented by separated splenic CD8(-) DC. In contrast, these T cells showed only weak, if any, proliferation in response to CD8(+) DC despite observable cluster formation in the cultures. The differential between the two DC types in inducing proliferation was even more pronounced than previously seen with primary T cells and did not reflect differential longevity of the DC in culture, altered response kinetics or deviation from IL-2 to IL-4 induction with CD8(+) DC, but was related to the levels of IL-2 induced. The deficiency in the CD8(+) DC was not overcome by using infectious virus rather than synthetic peptide as the antigen source. These results show that lymphoid-related CD8(+) splenic DC, despite their mature phenotype, fail to provide appropriate signals to secondary CD4(+) T cells to sustain their proliferation.

Identification of murine B-cell and T-cell epitopes of Escherichia coli outer membrane protein F with synthetic polypeptides

The major pore-forming outer membrane proteins (Omps) of gram-negative bacteria demonstrate numerous immunomodulating properties and are involved in the virulence of pathogenic strains. Because Escherichia coli OmpF is the best-characterized porin in terms of structural and functional characteristics, in vitro B-cell and T-cell responses to this porin in six different strains of mice were analyzed. Mice were immunized with purified OmpF trimers or overlapping synthetic polypeptides (20-mers) spanning the entire 340-amino-acid sequence of the OmpF monomer. T-cell proliferative responses and immunoglobulin G antibody responses to native OmpF and the peptide analogues were determined. For each strain, patterns of T-cell proliferation were similar regardless of whether native OmpF or synthetic peptides were inoculated, although all strains recognized one or more cryptic determinants. Mice exhibited several haplotype-specific responses, but genetically permissive epitopes were also identified. Four peptides (75-94, 265-284, 295-314, and 305-324) elicited strong T-cell proliferative responses from all strains of mice when mice were presensitized with native OmpF or a homologous peptide. In general, 10 or fewer peptides were recognized by sera from mice immunized with native OmpF or synthetic peptides, and most sera from peptide-immunized mice reacted poorly with the native protein. Four peptides spanning amino acids 45 to 64, 95 to 114, 115 to 134, and 275 to 294 were recognized by sera from all strains immunized with native OmpF but not by sera from peptide-immunized mice. Peptides 245-264 and 305-324 were universally recognized by sera from peptide-immunized mice, but these sera reacted weakly or were negative when tested against the native protein. Based on the pattern of cytokine secretion by proliferating T cells, immunization with native OmpF polarizes T helper cells toward development of a TH1 response. T-cell and B-cell responses have been investigated based on the assumption that differences in epitope specificity could influence protective or pathologic host reactions. Because of the high level of structural homology of OmpF to porins isolated from other enteric pathogens, the identification of T- and B-cell-stimulatory determinants of E. coli OmpF may have broader application.

The geometry of synthetic peptide-based immunogens affects the efficiency of T cell stimulation by professional antigen-presenting cells

In the pathway leading to antibody production there are two points at which CD4(+) T(h) cells need to be recruited. The first of these is priming of T cells by their interaction with dendritic cells (DC) bearing antigen presented on MHC class II molecules and the second is the collaborative interaction of these primed T cells with B cells presenting the same antigen. We have previously shown that the configuration of T and B cell determinants within synthetic peptide immunogens can greatly influence the amount of immunogen required to produce an antibody response. Here we investigate whether the difference in potency of different immunogens is related to their ability to be presented by either DC or B cells. We show that determinants in a branched configuration, which are the most efficient at eliciting antibody in vivo, are presented to T cell clones by splenic CD8(-) DC 10-fold more efficiently than the corresponding determinants in a tandem linear arrangement. B cells also showed preferential presentation of branched immunogens to one T cell clone but in contrast to DC, not to a second T cell clone, indicating differences between the two antigen-presenting cell types. We also show that branched immunogens have a greater stability in serum compared to linear peptides, which may further enhance the differences in their in vivo potency.

Preparation and properties of totally synthetic immunogens

Although the induction of antibodies and T cells by synthetic peptides representing defined antigenic determinants is a routine laboratory procedure, their use as vaccines has not yet been generally realised. There are a number of reasons for this and paramount is the limitation of valency which affects not only immunogenicity, but also the coverage of the antigenic universe. This paper is a review of our own work in which we have assembled synthetic peptides into multivalent artificial proteins and then examined their immunological properties.

Antigenic and immunogenic properties of totally synthetic peptide-based anti-fertility vaccines

In this study we describe the results of experiments in which a variety of totally synthetic luteinizing hormone releasing hormone (LHRH) vaccines were assembled and examined for their abilities to elicit antibody responses and induce sterility in mice. It is shown that totally synthetic vaccines consisting of a 15 residue-defined T cell epitope and the 10 residue LHRH epitope not only induced high titers of antibody but also induced sterility. This effect did not appear to correlate with antibody titer, antibody isotype or comparative antibody affinity, but may be related to the length of time for which antibodies are present to exert their influence.

Free radical induced polymerization of synthetic peptides into polymeric immunogens

Free radical induced polymerization of vinyl monomers such as the acryloyl peptides described here is a facile and rapid reaction used routinely, for example, in the polymerization of acrylamide and bisacrylamide for the assembly of polyacrylamide gels. The technology allows the incorporation of many of the same or different peptide determinants into a single polymer chain. In this study large polymers containing multiple copies of peptides representing T- and B-cell determinants of influenza haemagglutinin were constructed. The determinants retained antigenicity after the polymerization procedure and the polymers were highly immunogenic; the levels of antibody obtained after a single dose of polymeric immunogen were at least as great as those achieved only after repeated doses of the equivalent monomeric peptide. The technology has a wide range of potential applications, not the least significant of which is the construction of designer immunogens for third generation vaccine candidates.

Immunogenicity of an aphthovirus chimera of the glycoprotein of vesicular stomatitis virus

An oligodeoxynucleotide coding for amino acids 139 through 149 of antigenic site A (ASA) of the VP1 capsid protein of the foot-and-mouth disease virus C3 serotype (FMDV C3) was inserted into three different in-frame sites of the vesicular stomatitis virus New Jersey serotype (VSV-NJ) glycoprotein (G) gene cDNA present in plasmid pKG97 under control of the bacteriophage T7 polymerase promoter. Transfection of these plasmids into CV1 cells coinfected with the T7 polymerase-expressing vaccinia virus recombinant vTF1-6,2 resulted in expression of chimeric proteins efficiently reactive with both anti-FMDV and anti-VSV G antibodies. However, in vitro translation of transcripts of these VSV-G/FMDV-ASA chimeric plasmids resulted in proteins that were recognized by anti-G serum but not by anti-FMDV serum, indicating a requirement for in vivo conformation to expose the ASA antigenic determinant. Insertion of DNA coding for a dimer of the ASA unidecapeptide between the VSV-NJ G gene region coding for amino acids 160 and 161 gave rise to a chimeric ASA-dimer protein designated GF2d, which reacted twice as strongly with anti-FMDV antibody as did chimeric proteins in which the ASA monomer was inserted in the same position or two other G-gene positions. For even greater expression of chimeric VSV-G/FMDV-ASA proteins, plasmid pGF2d and a deletion mutant p(delta)GF2d (G protein deleted of 324 C-terminal amino acids) were inserted into baculovirus vectors expressing chimeric proteins GF2d-bac and deltaGF2d-bac produced in Sf9 insect cells. Mice vaccinated with three booster injections of 30 microg each of partially purified GF2d-bac protein responded by enzyme-linked immunosorbent assay with FMDV antibody titers of 1,000 units, and those injected with equivalent amounts of deltaGF2d-bac protein showed serum titers of up to 10,000 units. Particularly impressive were FMDV neutralizing antibody titers in serum of mice vaccinated with deltaGF2d-bac protein, which approached those in the sera of mice vaccinated with three 1-microg doses of native FMDV virions. Despite excellent reactivity with native FMDV, the anti-deltaGF2d-bac antibody present in vaccinated mouse serum showed no capacity to bind to sodium dodecyl sulfate (SDS)-denatured FMDV virions and only minimal reactivity with VP1 protein by Western blotting (immunoblotting) after SDS-polyacrylamide gel electrophoresis. It was also shown in a competitive binding assay that a synthetic ASA unidecapeptide, up to concentrations of 200 microg/ml, was quite limited in its ability to inhibit binding of anti-deltaGF2-bac antibody to native FMDV virions. These results suggest that the chimeric VSV-G/FMDV-ASA proteins mimic the capacity of FMDV to raise and react with neutralizing antibodies to a restricted number of ASA conformations present on the surface of native FMDV particles.