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

Evaluation of an adjuvanted hydrogel-based pDNA nanoparticulate vaccine for rabies prevention and immunocontraception

Immunocontraceptive vaccination is becoming an acceptable strategy in managing animal populations. Mass vaccination of dogs is the most cost-effective and efficient method to control rabies, and combination of rabies vaccination and animal population control will be an added advantage. In this study, we developed an adjuvanted hydrogel-based pDNA nanoparticulate vaccine for rabies protection and immunocontraception. In vivo, we observed an immune response skewed toward a Th2 type, in contrast to the Th1 type in our previous pDNA study. The observation was verified by the IgG2a/IgG1 ratio (<1), and cytokine expression profile of IL-4 and IFN-γ. The humoral immune response is key for rabies protection and a GnRH antibody-based immunocontraception. In mice, anti-GnRH antibody titers were detected 4 weeks after immunization and lasted for 12 weeks, post animal experiment was terminated. The adjuvanted pDNA nanoparticulate vaccine shows promise for future studies evaluating protection from rabies challenge and prevention of animal breeding.

Effect of gonadotropin-releasing hormone vaccination on T lymphocyte changes in male rats

The aim of this study was to detect the effect of immunization against gonadotropin-releasing hormone (GnRH) on cell-meditated immunity. Three-week-old male Sprague-Dawley rats (n=32) were randomly and equally assigned to two groups: 1) GnRH-tandem-ovalbumin immunized group; and 2) the control group (injected with an equivalent Al(OH)₃ adjuvant). Blood samples were collected at two-week intervals to assess the level of GnRH-specific antibodies and testosterone. Moreover, blood and thymus samples were also collected to analyze the T lymphocyte subpopulations one and two months after the last booster immunization. T lymphocyte immunity against GnRH was activated during the first month post-immunization as exhibited by increased numbers of CD3+ (P<0.05) and CD4+ (P<0.05)T lymphocytes following testosterone suppression (P<0.01), which was then restored and maintained at appropriate levels in the second month. In contrast, the differentiation of T lymphocytes in the thymus was reduced during the first month after immunization as exhibited by the significant decreased number of CD3+ (P<0.05) cells, followed by the restoration and heightened numbers at later time points for both the number of CD3+ (P<0.05) and CD4+ (P<0.01)T lymphocytes. These results suggest that immunization against GnRH interferes with the number of lymphocytes during the early time points following immunization. The number of T lymphocytes initially decreased in the peripheral blood following immunization, but was replenished by newly exported cells from the thymus which eventually restored the T lymphocytes to normal levels.

Synthetic B-Cell Epitopes Eliciting Cross-Neutralizing Antibodies: Strategies for Future Dengue Vaccine

Dengue virus (DENV) is a major public health threat worldwide. A key element in protection from dengue fever is the neutralising antibody response. Anti-dengue IgG purified from DENV-2 infected human sera showed reactivity against several peptides when evaluated by ELISA and epitope extraction techniques. A multi-step computational approach predicted six antigenic regions within the E protein of DENV-2 that concur with the 6 epitopes identified by the combined ELISA and epitope extraction approach. The selected peptides representing B-cell epitopes were attached to a known dengue T-helper epitope and evaluated for their vaccine potency. Immunization of mice revealed two novel synthetic vaccine constructs that elicited good humoral immune responses and produced cross-reactive neutralising antibodies against DENV-1, 2 and 3. The findings indicate new directions for epitope mapping and contribute towards the future development of multi-epitope based synthetic peptide vaccine.

Design, synthesis and evaluation of a gonadotropin releasing hormone-based subunit vaccine in rams (Ovis aries)

Immunocastration using gonadotropin-releasing hormone (GnRH)-based vaccines has been investigated in rams to reduce aggressive and sexual behaviour and to control meat quality. Despite considerable efforts, a practical GnRH vaccine has yet to be developed for rams. In the present study, a A GnRH-lipopeptide vaccine (GnRH-LP) including two copies of GnRH, 2-amino-d,l-hexadecanoic acid (C16), and a unique T helper epitope, was examined in rams. Rams received a primary and secondary vaccination of GnRH-LP without additional adjuvant (Group 1) or with the adjuvant AdjuVac™ (Group 2). In both Group 1 and 2 anti-GnRH antibody titres increased after secondary vaccination, however, the antibody titres were higher (p<0.01) for rams in Group 2. The latter rams showed a marked decrease in testicular size. The marked and sustained reduction in testicular size in rams treated with GnRH-LP+AdjuVac™ provides the basis for an effective immunocastration vaccine in rams.

The compensatory expression of reproductive hormone receptors in the thymus of the male rat following active immunization against GnRH

To determine whether hormone-receptor signaling pathways in the thymus are altered by active immunization against gonadotrophin-releasing hormone I (GnRH), 3-week-old Sprague-Dawley male rats received GnRH-tandem-OVA peptides (200 μg/ml), and the effects were compared to a control group. Serum testosterone, LH and FSH concentrations were markedly reduced, with severe testicular atrophy, compared to controls, demonstrating effective blockade of the pituitary-gonadal axis. The reduction in LH and FSH concentrations in the thymus of immunized animals was lower than that observed in the serum, where a significant difference (P<0.001) in concentration was observed between both groups. Concentrations of GnRH were increased in the thymus of immunized rats. In thymic tissue, GnRHR, FSHR and LHR demonstrated stronger immunostaining, and AR weaker staining, in the immunized group compared to controls. Reproductive hormone receptor mRNA expression was consistent with protein variations in the immunized thymus. Compared to controls, GnRHR gene levels were significantly increased (P<0.05), however, AR mRNA expression were greatly decreased with immune week-age (P<0.05). Both FSHR and LHR mRNA expression levels were significantly higher in the treated group than in controls in the first three samples (P<0.05). When GnRHR was blocked by an antagonist in thymocytes, all reproductive hormone receptor gene expressions were significantly increased (P<0.001). In summary, these findings suggest that active immunization against GnRH can up-regulate GnRH receptor and gonadotropin receptor signaling, by stimulating thymic autocrine and paracrine function, whereas the androgen receptor is down-regulated due to a lack of testosterone secretion in the thymus.

Very small size proteoliposomes (VSSP) and Montanide combination enhance the humoral immuno response in a GnRH based vaccine directed to prostate cancer

Very small size proteoliposomes (VSSP) constitute a complex of very small size proteoliposomes that includes proteins, lipids, CpG and gangliosides tumor-associated that provides a potential target for cancer immunotherapy. This compound has been described to stimulate the humoral and cellular response, dendritic cells (DC) activation and differentiation of T-helper cells, specially, in immunocompromised patients with cancer status. This work deals with the stimulating capacity of the VSSP to reach a humoral response when they are used as a component in a peptidic vaccine based on the gonadotrophin releasing hormone (GnRH). This study was carried out in male Copenhagen rats, which were immunized with 750μg of the GnRH mimetic peptide (GnRHm1-TT) with or without the VSSP. The mixtures were always emulsified with the oil adjuvant Montanide ISA 51. The anti GnRH seroconversion analysis revealed that the group immunized with the peptide GnRHm1-TT/VSSP developed a strong anti GnRH seroconversion. These antibody levels proved to be significant superior to those reached by the use of the GnRHm1-TT peptide solely emulsified in Montanide. Post-mortem analysis on the Testosterone ablation target organs (prostate and testicles) yielded a sudden decrease in their size and weight in respect to the control group. On the other hand, the group submitted to the use of GnRHm1-TT/VSSP, showed a significant difference in the reduction of these target organs in comparison with the group only immunized with GnRHm1-TT adjuvated in Montanide ISA 51. These values turned to be of p=0.023 and p=0.009 in the prostate and testicles respectively. These findings foreground the VSSP as a useful immunopotentiator to be used as part of a GnRH based vaccine to treat prostate cancer.

Current status of multiple antigen-presenting peptide vaccine systems: Application of organic and inorganic nanoparticles

Many studies are currently investigating the development of safe and effective vaccines to prevent various infectious diseases. Multiple antigen-presenting peptide vaccine systems have been developed to avoid the adverse effects associated with conventional vaccines (i.e., live-attenuated, killed or inactivated pathogens), carrier proteins and cytotoxic adjuvants. Recently, two main approaches have been used to develop multiple antigen-presenting peptide vaccine systems: (1) the addition of functional components, e.g., T-cell epitopes, cell-penetrating peptides, and lipophilic moieties; and (2) synthetic approaches using size-defined nanomaterials, e.g., self-assembling peptides, non-peptidic dendrimers, and gold nanoparticles, as antigen-displaying platforms. This review summarizes the recent experimental studies directed to the development of multiple antigen-presenting peptide vaccine systems.

A lipopeptide based on the M2 and HA proteins of influenza A viruses induces protective antibody

A conserved 15 amino-acid residue sequence of the ectodomain of the M2 protein of influenza A virus (M2e) induces a strong antibody (Ab) response when incorporated into a synthetic lipopeptide vaccine candidate containing a T-helper epitope from influenza A hemagglutinin and the dendritic cell-targeting lipid moiety S-[2,3-bis(palmitoyloxy)propyl]cysteine (Pam2Cys). Abs elicited by the truncated M2e sequence were specific for the M2 protein of influenza A virus and were also capable of binding to cells that were infected with influenza A viruses of different subtypes. The Ab titres against the lipopeptide were similar in magnitude to those elicited by the full-length (23 residue) M2e peptide when administered in Freund's adjuvant. Abs to the truncated M2e sequence were also able to significantly reduce the viral load in airways of BALB/c mice after challenge with live influenza virus.

The hinge region fragment of immunoglobulin G improves immunogenicity of recombinant gonadotrophin-releasing hormone conjugated to the T-helper epitope in designing peptide vaccines

In our previous study, the hinge fragment (225-232/225'-232') of human immunoglobulin G1 (IgG1) was used as a space peptide linker for synthesizing the GnRH3-hinge-MVP chimeric peptide, whereby three repeated gonadotrophin-releasing hormone (GnRH) units and a T-cell epitope from measles virus fusion protein (MVP) were amide-bond-linked at the N and C terminus, respectively, to the hinge peptide for producing anti-GnRH antibody responses. To investigate whether or not the hinge region fragment can improve the immunogenicity of GnRH, we further synthesized and purified GnRH3-hinge-MVP, GnRH3-hinge and GnRH3-MVP using recombinant DNA technology. Under high pH conditions, GnRH3-hinge-MVP was capable of forming double-chain structures. Immunization of male mice with the immunogens of GnRH3-hinge-MVP resulted in the generation of high-titre antibodies specific for GnRH. The synthetic GnRH3-hinge and GnRH3-MVP induced a lower titre of anti-GnRH antibody than GnRH3-hinge-MVP. This was followed by a decrease in serum testosterone levels, which resulted in a low level of expression of the relaxin-like factor gene in the testis. Our data suggest that peptide and T-cell epitopes oriented at the N-terminus or C-terminus of hinge peptides simplify the antigenic peptide conjugates and may be considered as potential synthetic immunogens.

Multiple antigenic peptides as vaccine platform for the induction of humoral responses against dengue-2 virus

Dengue is an important agent of human disease for which no licensed vaccine is available to the public. We used multiple antigenic peptides (MAPs) as an antigen carrier for the development of subunit vaccines against dengue-2 virus (DEN-2). Commercially available software (MacVector 7.0) was used to identify potential antigenic B-cell epitopes of E-glycoprotein. A total of 60 BALB/c mice were immunized with 12 recombinant DEN-2-specific MAPs and the humoral immune response was assessed by anti-DEN-2 ELISA and PRNT50 assays. Anti-DEN-2 ELISA showed high levels of anti-DEN-2 antibodies and post-immune sera reduced viral infectivity and prevented infection of monkey kidney cells (LLC-MK2) with live DEN-2 virus. Seven neutralizing DEN-2 epitopes were identified that generated PRNT50 titers of up to 1:160. Our findings show that the MAP platform can be used as an antigen-presenting platform for dengue vaccine development.

Synthesis of toll-like receptor-2 targeting lipopeptides as self-adjuvanting vaccines

Effective Th1- and Th2-type immune responses that result in protective immunity against pathogens can be induced by self-adjuvanting lipopeptides containing the lipid moiety dipalmitoyl-S-glyceryl cysteine (Pam2Cys). The potent immunogenicity of these lipopeptides is due to their ability to activate dendritic cells by targeting and signaling through Toll-like receptor-2 (TLR-2). In addition, the simplicity and flexibility in their design as well as their ease of chemical definition and characterisation makes them highly attractive vaccine candidates for humans and animals. We describe in this chapter the techniques involved in the synthesis of an immunocontraceptive lipopeptide vaccine as well as the experimental assays carried out to evaluate its efficiency.

Immunotherapy of prostate cancer in a murine model using a novel GnRH based vaccine candidate

Previous studies with gonadotrophin releasing hormone (GnRH/LHRH) vaccines have shown the usefulness of immunization against this hormone in prostate cancer. To this end, we have generated a completely synthetic peptide modified at position 6 and attached to the 830-844 tetanic toxoid (TT) helper T cell sequence. Through this work we have demonstrated that the GnRHm1-TT molecule was highly immunogenic when it is formulated as an oil-based emulsion adjuvated with Montanide ISA 51. That results correlated directly with testosterone reduction and tumor growth inhibition of the Dunning R3327-H androgen responsive prostate tumor model in rats. GnRHm1-TT, proved to be safe and useful for future clinical trials.

Totally synthetic peptide-based immunocontraceptive vaccines show activity in dogs of different breeds

In this study we examine the immunogenicity of totally synthetic peptide-based immunocontraceptive vaccines in dogs. Seven individual epitope-based vaccines were assembled in which a different T helper (T(H)) cell epitope derived from the sequence of F protein of canine distemper virus was synthesized in tandem with a peptide representing luteinising hormone releasing hormone (LHRH). Each of the individual T(H)-LHRH peptide vaccines was inoculated subcutaneously into dogs. The results demonstrate that five of the seven peptide vaccines were able to elicit strong anti-LHRH antibody responses in beagle foxhounds accompanied by a concomitant suppression in the levels of the hormones testosterone and progesterone in the majority of the animals. A pool of these five peptides was then used to inoculate five different breeds of dogs. All animals responded with high levels of anti-LHRH antibody. An investigation of the proliferative responses of peripheral blood mononuclear cells (PBMC) obtained from inoculated dogs showed that the majority of breeds responded to each of the individual T helper cell epitope tested. The results provide a strategy for development of an immunocontraceptive vaccine for use in multiple breeds of dogs.

The C-terminal pentapeptide of LHRH is a dominant B cell epitope with antigenic and biological function

Luteinizing hormone releasing hormone (LHRH) has been intensively studied as a target for the control of fertility and hormone dependent cancers. In most studies a decapeptide, EHWSYGLRPG, which is identical to the native LHRH sequence, has been used. In this study we investigated whether short sequences of LHRH could retain immunogenic and antigenic properties and be employed in a vaccine preparation. Our results show that the C-terminal five-residue peptide (LHRH(6-10)) of LHRH was able to inhibit the binding of anti-LHRH(1-10) antisera to LHRH(1-10) in an inhibition ELISA. A totally synthetic peptide vaccine incorporating LHRH(6-10) also elicited a strong anti-LHRH antibody response and prevented mice from becoming pregnant in fertility trials. The primary immune response elicited by a peptide vaccine based on LHRH(1-10) could be boosted with LHRH(6-10). Finally, an antigen system comprising of biotinylated LHRH(6-10) bound to streptavidin-coated plates was capable of discriminating between anti-LHRH antibodies present in fertile and non-fertile mice. This study demonstrates that LHRH(6-10) retains immunogenic and antigenic properties and also discerns antibody specificities associated with reproductive competence.

A self-adjuvanting multiepitope immunogen that induces a broadly cross-reactive antibody to hepatitis C virus

We describe a peptide-based strategy for HCV vaccine design that addresses the problem of variability in hypervariable region 1 (HVR1). Peptides representing antibody epitopes of HVR1 from genotype 1a were synthesized and incorporated into multideterminant immunogens that also included lipid moieties and helper T (T(h)) cell epitopes. Mice inoculated with these polyepitopes generated strong antibody responses. Antibody titers were highest in mice inoculated with polyepitope immunogens which contained the lipid moiety dipalmitoyl-S-glyceryl cysteine (Pam2Cys). Antisera were tested for their potential to neutralize HCV by 3 currently available assays. Antibodies elicited in mice by the polyepitope-based vaccine candidates were able to (1) bind to E2 expressed on the surface of E1/E2-transfected human embryonic kidney (HEK) 293T cells, (2) capture HCV of different genotypes (1, 2, and 3) from the serum of chronically infected humans in an immune capture RT-PCR assay and (3) inhibit HCVpp entry into Huh7 cells. Antibody present in the sera of patients chronically infected with HCV genotypes 1, 2, 3, and 4 also bound to the HVR1-based polyepitope.

CONCLUSION

These results demonstrate the potential of self-adjuvanting epitope-based constructs in the development and delivery of cross-reactive immunogens that incorporate potential neutralizing epitopes present within the viral envelope of HCV.

Immunisation of male mice with a plasmid DNA vaccine encoding gonadotrophin releasing hormone (GnRH-I) and T-helper epitopes suppresses fertility in vivo

Immunisation against mammalian gonadotrophin releasing hormone (GnRH-I) linked to large carrier proteins has been shown to disrupt fertility. However, various studies have shown that the carrier protein causes epitope suppression of the hapten response, resulting in short-lived immunoneutralisation, followed by a return of fertility. A range of strategies has been used to resolve this, with limited success. The aim of this study was to construct a plasmid DNA vaccine encoding GnRH-I and T-helper epitopes. A 498 bp long vaccine construct in pcDNA3.1+ was administered to male mice in conjunction with a Hemagglutinating Virus of Japanese Envelop (HVJ-E) vector or in saline solution. The vaccine efficacy was evaluated in terms of GnRH-I specific IgG antibody response, serum testosterone levels, testicular spermatogenesis and the ability to produce offspring. The vaccine appeared to induce higher anti-GnRH-I IgG antibody response and insult the fertility axis, which was characterised by a drop of epididymal sperm counts, reduction of serum testosterone levels, suppressed testicular spermatogenesis and a significant decrease in litter numbers compared to control animals. The end-point vaccine efficacy was much higher in the HVJ-E vector mediated immunisation, than in saline alone.

Comparison of lipopeptide-based immunocontraceptive vaccines containing different lipid groups

We have previously shown that incorporating the lipid moiety dipalmitoyl-S-glyceryl cysteine (Pam2Cys) into peptide structures effectively adjuvants otherwise weak immunogens. In this study lipopeptides based on luteinising hormone releasing hormone (LHRH) as a B cell epitope, [B], were synthesised in tandem with a 17-residue T-helper epitope, [T], derived from the fusion protein of the morbillivirus canine distemper virus. In this way vaccine candidates with the structure [T]-[B] were produced. These peptides were then lipidated with different diacylated moieties. The acyl moieties used were: palmitic acid (C16) to give Pam2Cys, stearic acid (C18) to give Ste2Cys, lauric acid (C12) to give Lau2Cys and octanoic acid (C8) to give Oct2Cys. We compared the immunogenicities of these simple lipopeptides in BALB/c mice by measuring their ability to induce anti-LHRH antibodies and found that immunogenicity was dependent on the length of the alkane chains of the incorporated lipid moieties with the hierarchy C16=C18>C12>C8. The antibody levels elicited by the lipopeptides also correlated with their ability to inhibit the reproductive capability of female mice in fertility trials. Furthermore, the C16 lipopeptide was the most effective in activating dendritic cells, measured by up regulation of surface MHC Class II molecules, and also in activating NF-kappaB in a Toll-like receptor-2 (TLR2)-dependent manner.

Identification of dominant epitopes of synthetic immunocontraceptive vaccines that induce antibodies in dogs

The specificities of immunoglobulin G antibodies obtained from the sera of dogs inoculated with totally synthetic immunocontraceptive vaccine candidates based on luteinising hormone releasing hormone (LHRH: amino acid sequence HWSYGLRPG) were examined using peptides expressed in a phage display library. The three vaccine candidates each contained a different T helper-cell epitope chemically linked with the same LHRH amino acid sequence HWSYGLRPG and all of them elicited high antibody titres against the hormone. Delineation of epitopes recognised by sera from vaccinated dogs using a phage display library indicated that two of the three vaccine candidates induced antibody directed to the consensus sequence xHWSxxLxxx whereas the third vaccine candidate induced antibody against the consensus sequence xxxxxxxRPx. Two of the three vaccine candidates elicited antibodies against B cell epitopes present within the helper T-cell epitope component of the vaccine whereas the third vaccine did not. The occurrence of anti-T helper cell epitope antibodies appeared to have little or no effect on the generation of the anti-LHRH responses indicating that carrier-induced epitope suppression was not operating here. Our results also demonstrated that with animal sera of high quality, it is possible to delineate immunodominant epitopes recognised by polyclonal antibodies with high efficiency using phage display library. The approach has utility in the definition of immunodominant epitopes, which may "decoy" antibody responses away from other epitopes, which may be more useful in prophylaxis or therapy.

A synthetic gonadotropin-releasing hormone (GnRH) vaccine for control of fertility and hormone dependent diseases without any adjuvant

Active immunization against self-peptides have gained widespread acceptance inspite of their low immunogenicity. Recent applications involving multiple copies of self-peptides in linear alignment and conjugation with carrier proteins appear to increase the immune response against self-peptides. As with most vaccines, however, immunogens require supplementation with adjuvants to elicit an optimum immune response. In the present study, we prepared a double-chain mini-protein with each chain containing three linear repeats of the self-peptide gonadotropin-releasing hormone (GnRH3), the hinge region of human IgG1 (hinge), and a T-helper epitope from the measles virus protein (MVP). The GnRH3-hinge-MVP mini-protein was conjugated to purified recombinant heat shock protein 65 (Hsp 65) of Mycobacterium bovis and used to immunize rats primed with subcutaneous injections of Bacillus Calmette-Guerin (BCG) in the absence of adjuvants. The GnRH3-hinge-MVP-Hsp 65 stimulated the production of specific anti-GnRH antibodies in the absence of adjuvants and the antibody titer was comparable to that produced in rats immunized with the dimeric mini-protein in the presence of Freund's adjuvant. Moreover, immunization with the adjuvant-free GnRH3-hinge-MVP-Hsp 65 induced degeneration of the reproductive organs in both male and female rats unlike those immunized in the absence of Hsp 65 or in control animals inoculated with the vehicle only. Histological examination of the affected organs showed atrophy of the seminiferous tubules with diminished spermatogenesis in the testes of male rats. In female rats, the uteri were much smaller in size and the ovaries exhibited reduced follicular development. These findings demonstrated that GnRH3-hinge-MVP-Hsp 65 mounted a strong immune response in the absence of conventional adjuvants, and could prove useful in control of fertility and the treatment of conditions/diseases where GnRH ablation is required.

Characterisation of the antibody response to a totally synthetic immunocontraceptive peptide vaccine based on LHRH

In this study we describe our attempts to improve the immunogenicity of a synthetic epitope-based vaccine. The vaccine consists of an epitope (P25) that is recognised by CD4+ helper T cells and the target epitope luteinising hormone releasing hormone (LHRH). We show that replacement of the single cysteine residue within P25 with amino acids such as alanine, aminobutyric acid, serine or with carboxymethylated cysteine leads to diminished immunogenicity of the vaccine and only the oxidised dimeric form of the peptide retains the full immunogenicity of the vaccine. Secondly, by measuring the serum antibody response and the number of the antigen secreting cells in spleen and bone marrow we found that three doses of 20 nmol per mouse induced the more consistent and higher immune responses than those induced by three doses of either 2 nmol or 80 nmol per mouse. A greater variation in antibody titre was observed in mice that received the 2 mol or 80 nmol dose regimes. Last, by administering the vaccine in its lipidated form in the presence or absence of additional adjuvant we found that either inoculation regime elicited similar antibody responses. Only at low doses of antigen was a synergistic effect observed when lipopeptide was co-administered with additional adjuvant.

A totally synthetic vaccine of generic structure that targets Toll-like receptor 2 on dendritic cells and promotes antibody or cytotoxic T cell responses

A simple generic peptide-based vaccine structure that targets Toll-like receptor 2-expressing dendritic cells and causes their activation is described. The vaccines are totally synthetic, serve as their own adjuvant, and are composed of (i) a single helper T cell epitope, (ii) a target epitope that is either recognized by CD8+ T cells or B cells, and (iii) a Toll-like receptor 2-targeting lipid moiety, S-[2,3-bis(palmitoyloxy)propyl]cysteine, that is situated between the peptide epitopes to form a branched configuration. The different CD8+ T cell epitopes examined were from (i) influenza virus, (ii) the intracellular bacterium Listeria monocytogenes, and (iii) ovalbumin as a model tumor antigen. Vaccines containing a B cell epitope from gastrin or luteinizing hormone-releasing hormone as a B cell epitope were also examined for their ability to elicit antibody against the parent hormones. Each of the vaccines was capable of inducing either CD8+ T cell or antibody-mediated immune responses. The lipidated vaccines, but not the nonlipidated vaccines, were able to mediate protection against viral or bacterial infection and mediate prophylactic and therapeutic anticancer activity. The two hormone-based vaccines induced high antibody titers, which in the case of luteinizing hormone-releasing hormone resulted in abrogation of reproductive function. These results highlight the utility of simple, totally synthetic, epitope-based vaccines.

Immune responses to a GnRH-based anti-fertility immunogen, induced by different adjuvants and subsequent effect on vaccine efficacy

A modified GnRH peptide (CHWSYGLRPG-NH2) was conjugated to tetanus toxoid and formulated with different adjuvants (non-ionic surfactant vesicles, aluminium hydroxide, Quil A, PLGA (poly(lactide-co-glycolide)/triacetin), and Quil A/PLGA). A comparison of the anti-fertility efficacy of the formulations was made by examining specific antibody levels, antibody subclasses, endocrine ablation and gonadal atrophy. The production of IgG2b antibody provided the best correlation for castration. PLGA was considered the most effective adjuvant as it produced a consistent anti-fertility response in all the treated animals.

The immunogenicity of recombinant and dimeric gonadotrophin-releasing hormone vaccines incorporating a T-helper epitope and GnRH or repeated GnRH units

In this study, we designed two linear peptides, GnRH-hinge-MVP, which consists of human gonadotrophin-releasing hormone (GnRH), hinge fragment 225-232/225'-232' of human IgG1 and a T helper peptide from measles virus protein (MVP), and GnRH3-hinge-MVP, which contains three copies of GnRH (so termed GnRH3). The DNA constructs encoding for the two peptides were fused to the C-terminal encoding sequence of asparaginase, encompassing residues 199-326, through an acid-labile aspartyl-prolyl linker. The chimeric genes were expressed at high levels in Escherichia coli. The fusion proteins were purified to approximate homogeneity by means of washing the inclusion bodies and by ethanol precipitation. The GnRH-hinge-MVP or the GnRH3-hinge-MVP was released from the fusion proteins by cleavage with hydrochloric acid and further oxidized into double-chain miniproteins after purification. Both dimeric constructs proved to be efficient immunogens. It was shown that rats immunized with the immunogens generated antibodies specific for GnRH. The dimeric GnRH3-hinge-MVP containing three copies of GnRH in each chain induced a higher titre of anti-GnRH antibodies than the GnRH-hinge-MVP, containing a single copy of GnRH in each chain. These results demonstrate that combining multicopies or single copies of peptide with hinge fragment of human IgG and T helper peptide from measles virus protein can induce anti-peptide immune responses. Our data also suggest that these methods of preparation and dimerization of the recombinant polypeptides may provide a useful strategy for other polypeptide vaccine developments.

A novel retro-inverso gonadotropin-releasing hormone (GnRH) immunogen elicits antibodies that neutralize the activity of native GnRH

GnRH vaccines have been successfully used for the inhibition of gonadotropin secretion and gonadal function. As an alternative to native GnRH, retro-inverso (RI) GnRH might be an improved immunogen. The RI peptides are composed of D-amino acids assembled in the reverse order (C to N terminus) in relation to the parent L peptide. These peptides are immunogenic and can produce high titers of antibodies that bind the parent peptide with high affinity and specificity. We show that RI-GnRH peptides conjugated to ovalbumin as well as unconjugated RI-GnRH elicit high titers of anti-GnRH antibodies in rabbits and mice. Antibodies were affinity purified and shown by ELISA to be selective for mammalian GnRH compared with GnRH II and [Gln(8)]GnRH. The binding kinetics of antibody-peptide interactions was determined using biosensor technology (BIACORE). The purified anti-GnRH antibodies inhibited GnRH-stimulated signal transduction in COS-1 cells expressing the human GnRH receptor. Immunization of mice with unconjugated and conjugated RI-GnRH peptide, in the absence of complete Freund's adjuvant, produced antisera that cross-reacted with mammalian GnRH. As RI peptides are resistant to cleavage by proteolytic enzymes, they are potentially orally active. The ability of RI-GnRH peptides to produce antibodies to GnRH without conjugation and without Freund's complete adjuvant constitutes a novel vaccine with improved properties of potential application in animal management and sex hormone-dependent cancers.

Lipid and carbohydrate based adjuvant/carriers in immunology

This review discusses various issues regarding vaccines; what are they and how they work, safety aspects, the role of adjuvants and carriers in vaccination, synthetic peptides as immunogens, and new technologies for vaccine development and delivery including the identification of novel adjuvants for mucosal vaccine delivery. There has been a recent increase of interest in the use of lipids and carbohydrates as adjuvants, and so a particular emphasis is placed on adjuvants derived from lipids or carbohydrates, or from both.

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.

Current advances in antifertility vaccines for fertility control and noncontraceptive applications

The search for effective antifertility vaccines has been actively pursued for decades in clinical applications as contraceptives or in the treatment of hormone-dependent conditions. More recently, innovations have seen immunocontraception being employed successfully in veterinary and farming applications, as well as in population control of a number of different wildlife species. Although the basic principle behind these vaccines is the same, design considerations and criteria for commercialization are very different. This review will examine current advances in this field and evaluate the future scope of antifertility vaccines.

Influence of carrier protein conjugation site and terminal modification of a GnRH-I peptide sequence in the development of a highly specific anti-fertility vaccine. Part I

PROBLEM

We previously immunoneutralized gonadotrophin releasing hormone (GnRH), using an analogue of GnRH (des-1 GnRH-I), conjugated to tetanus toxoid via a carbodiimide reaction. The castration effect on the reproductive system was not consistent in all the treated animals. Therefore, we examined the possibility that conjugation to the carrier protein via the N- or C-terminal could have an effect on efficacy.

METHOD OF STUDY

GnRH analogue sequences were synthesized consisting of an additional cysteine at either terminal and specific conjugation was carried out using a bifunctional linker agent.

RESULTS

Conjugation of the monomer through the N-terminal proved to be a highly effective means of causing immunocastration in terms of decreased gonadotrophin and testosterone concentrations and testicular size, whereas conjugation through the C-terminal proved to be ineffective. This was reflected in the ability of the antibodies to bind native GnRH, but not the levels of the anti-GnRH antibodies.

CONCLUSION

Immunoneutralization efficacy was attributed to the importance of preserving the GnRH C-terminal.

Part II: influence of dimerization of a modified GnRH-I peptide sequence on a male antifertility vaccine

PROBLEM

In the previous paper, we described how the tetanus toxoid (TT) conjugated monomer, CHWSYGLRPG-NH2, induced high neutralizing antibody titres, which resulted in decreased levels of testosterone and subsequent antifertility. However, its counterpart HWSYGLRPGC, induced low avidity antibody titres. We wanted to know whether peptide dimerization would improve the efficacy of both peptides.

METHOD OF STUDY

Male Sprague-Dawley rats were immunized with modified dimerized GnRH-I peptides (HWSYGLRPGCCGPRLGYSWH and GPRLGYSWHCCHWSYGLRPG-NH2), with or without conjugation to TT.

RESULTS

The unconjugated dimers were not effective in causing castration, although the first peptide dimer did induce production of antibodies. When conjugated to TT, both dimers showed the same level of efficacy in causing castration as each other. However, there were differences in antibody binding to native GnRH.

CONCLUSIONS

Dimerization and conjugation to a carrier improved the antifertility efficacy of HWSYGLRPGC, whereas the conjugated monomer CHWSYGLRPG-NH2 showed a greater level of consistent castration than its conjugated dimer.

Performance of male pigs immunized against GnRH is related to the time of onset of biological response

In this study, the performance of male pigs immunized against GnRH was determined in relation to the onset of their biological response to the immunization. Pigs were immunized at 9 and 17 wk of age and were housed in a pen together with both a surgically castrated and an intact boar littermate. Feed intake was restricted to 2.8 to 3.2 times maintenance requirement for energy. Animals were weighed weekly and slaughtered at 108 kg BW. Depending on the time of onset of the response after immunization in terms of biological effects, immunized pigs were retrospectively grouped into two categories. One category consisted of the immunized pigs, which had undetectable or low levels of LH and testosterone at the time of booster immunization-known as "early" responding immunocastrates (E-IM, n = 8), whereas the "late" responding immunocastrates (L-IM, n = 7) had substantial LH and testosterone levels at that time. This dichotomy of the response to immunization also was reflected in testis weight, with 17 g and 40 g for E-IM and L-IM pigs, respectively. At slaughter, testis size and weight were reduced (P < 0.001) in the immunocastrated pigs as compared to the intact boars. Androstenone concentrations in backfat of all immunocastrated pigs were undetectable. Growth performance (i.e., ADG and feed efficiency [FE, g gain/kg feed]), was better in boars and L-IM pigs than in surgical castrates and E-IM pigs (P < 0.05). Average daily gain and FE did not differ between E-IM pigs and the surgical castrates, but intact boars performed better than L-IM (P < 0.02). There were no significant differences in carcass quality (backfat thickness and meat percentage) between boars and surgical castrates at slaughter. However, for both characteristics L-IM pigs and intact boars performed better (P < 0.03) than E-IM pigs. Thus, growth performance in L-IM is better than in either E-IM or surgical castrates.

Highly immunogenic and totally synthetic lipopeptides as self-adjuvanting immunocontraceptive vaccines

In this study, we describe the synthesis of various lipopeptides based on the sequence of luteinizing hormone-releasing hormone (LHRH) and report on their abilities to induce Abs against this "self" hormone when inoculated into mice in the absence of additional adjuvant. The peptides consisted of a colinear CD4(+) T helper cell epitope from the L chain of influenza virus hemagglutinin and LHRH, which has B cell epitopes but no T cell epitopes present in its sequence. Lipids were attached either at the N terminus or between the T cell epitope and LHRH, in the approximate center of the peptide. The lipopeptide constructs displayed different solubilities and immunological properties that depended not only on the lipid content but also on the position of attachment of the lipids. Some of these constructs were highly immunogenic, inducing high titers of Ab, which were capable of efficiently sterilizing female mice when administered in saline by s.c. or intranasal routes. The most effective vaccines were highly soluble, contained the dipalmitoyl-S-glyceryl cysteine moiety, and had this lipid attached at the center of the molecule. The relative ability of the lipopeptides to induce an Ab response in the absence of external adjuvant was reflected by their ability to up-regulate the surface expression of MHC class II molecules on immature dendritic cells. These results demonstrate that the composition and position within peptide vaccines of self-adjuvanting lipid groups can influence the ability to induce the maturation of dendritic cells and, in turn, the magnitude of the resulting Ab response.

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.

Enhanced immunogenicity of a contraceptive vaccine using diverse synthetic carriers with permissible adjuvant

A vaccine directed against human chorionic gonadotropin (hCG) has previously undergone clinical testing demonstrating the feasibility of the approach in preventing pregnancy in women. Some individuals, however, did not respond adequately despite employing highly immunogenic bacterial toxoids as carriers. We investigated the potential of three promiscuous pathogen-derived Th peptides as carriers, employing alum as the adjuvant. While conjugation with each peptide improved the antibody response against hCG in mice of different haplotypes, immunisation with a combination of these peptide-conjugates generated anti-hCG responses higher than those achieved with the individual peptides or tetanus toxoid (TT). Antibodies were of high affinity and capable of neutralising the bioactivity of hCG but were devoid of anti-peptide reactivity. These results have implication for the design of hCG vaccine with improved immunogenicity for diverse population.

Humoral hyporesponsiveness to a conjugate contraceptive vaccine and its bypass by diverse carriers using permissible adjuvant

A contraceptive vaccine directed against human chorionic gonadotropin (hCG) has previously undergone clinical testing that demonstrated the feasibility of the approach in preventing pregnancy in women. Some immunized volunteers however, did not respond with an adequate anti-hCG antibody response despite employing highly immunogenic bacterial toxoids as carriers. Since there is some evidence that T cell responses to a complex protein typically focus on a few immunodominant epitopes, we investigated the responsiveness to hCG in mice of different haplotypes using the protein carrier diphtheria toxoid (DT). Our data showed a differential carrier effect of DT. With the aim of making a more potent immunogen employing promiscuous pathogen-derived Th peptides as carriers, peptide:antigen stoichiometric ratios were optimized. When tested individually using alum as the adjuvant, three such peptide conjugates improved the anti-hCG response, though not consistently to levels higher than the DT conjugate. Immunization with a combination of these synthetic epitopes generated anti-hCG responses higher than those achieved with DT or with the individual peptides. Antibodies were of high affinity and capable of neutralizing the bioactivity of hCG, but were devoid of anti-peptide reactivity. These results support our view that differential hyporesponsiveness in a diverse population may arise from inadequate carrier effect and that it can be overcome by use of pathogen-derived broadly reactive non-B Th epitopes employing only alum, a permissible adjuvant.