The central role played by peptides in the immune response and the design of peptide-based vaccines against infectious diseases and cancer

Selection of vaccine-candidate peptides from Mycobacterium avium subsp. paratuberculosis by in silico prediction, in vitro T-cell line proliferation, and in vivo immunogenicity

Mycobacterium avium subspecies paratuberculosis (MAP) is a global concern in modern livestock production worldwide. The available vaccines against paratuberculosis do not offer optimal protection and interfere with the diagnosis of bovine tuberculosis. The aim of this study was to identify immunogenic MAP-specific peptides that do not interfere with the diagnosis of bovine tuberculosis. Initially, 119 peptides were selected by either (1) identifying unique MAP peptides that were predicted to bind to bovine major histocompatibility complex class II (MHC-predicted peptides) or (2) selecting hydrophobic peptides unique to MAP within proteins previously shown to be immunogenic (hydrophobic peptides). Subsequent testing of peptide-specific CD4+ T-cell lines from MAP-infected, adult goats vaccinated with peptides in cationic liposome adjuvant pointed to 23 peptides as being most immunogenic. These peptides were included in a second vaccine trial where three groups of eight healthy goat kids were vaccinated with 14 MHC-predicted peptides, nine hydrophobic peptides, or no peptides in o/w emulsion adjuvant. The majority of the MHC-predicted (93%) and hydrophobic peptides (67%) induced interferon-gamma (IFN-γ) responses in at least one animal. Similarly, 86% of the MHC-predicted and 89% of the hydrophobic peptides induced antibody responses in at least one goat. The immunization of eight healthy heifers with all 119 peptides formulated in emulsion adjuvant identified more peptides as immunogenic, as peptide specific IFN-γ and antibody responses in at least one heifer was found toward 84% and 24% of the peptides, respectively. No peptide-induced reactivity was found with commercial ELISAs for detecting antibodies against Mycobacterium bovis or MAP or when performing tuberculin skin testing for bovine tuberculosis. The vaccinated animals experienced adverse reactions at the injection site; thus, it is recommend that future studies make improvements to the vaccine formulation. In conclusion, immunogenic MAP-specific peptides that appeared promising for use in a vaccine against paratuberculosis without interfering with surveillance and trade tests for bovine tuberculosis were identified by in silico analysis and ex vivo generation of CD4+ T-cell lines and validated by the immunization of goats and cattle. Future studies should test different peptide combinations in challenge trials to determine their protective effect and identify the most MHC-promiscuous vaccine candidates.

Immunoinformatics-Based Identification of the Conserved Immunogenic Peptides Targeting of Zika Virus Precursor Membrane Protein

Zika virus infections lead to neurological complications such as congenital Zika syndrome and Guillain-Barré syndrome. Rising Zika infections in newborns and adults have triggered the need for vaccine development. In the current study, the precursor membrane (prM) protein of the Zika virus is explored for its functional importance and design of epitopes enriched conserved peptides with the usage of different immunoinformatics approach. Phylogenetic and mutational analyses inferred that the prM protein is highly conserved. Three conserved peptides containing multiple T and B cell epitopes were designed by employing different epitope prediction algorithms. IEDB population coverage analysis of selected peptides in six different continents has shown the population coverage of 60-99.8% (class I HLA) and 80-100% (class II HLA). Molecular docking of selected peptides/epitopes was carried out with each of class I and II HLA alleles using HADDOCK. A majority of peptide-HLA complex (pHLA) have HADDOCK scores found to be comparable and more than native-HLA complex representing the good binding interaction of peptides to HLA. Molecular dynamics simulation with best docked pHLA complexes revealed that pHLA complexes are stable with RMSD <5.5Å. Current work highlights the importance of prM as a strong antigenic protein and selected peptides have the potential to elicit humoral and cell-mediated immune responses.

The Bioinformatic and In Vitro Studies of Clostridioides Difficile Aminopeptidase M24 Revealed the Immunoreactive KKGIK Peptide

Clostridioides difficile (CD) is a Gram-positive pathogen responsible for CD-associated disease (CDAD), which is characterized by symptoms ranging from mild diarrhea to pseudomembranous colitis. This work is an attempt to respond to the need of novel methods for CD infection (CDI) prevention, since the number of CDI cases is still rising. A bioinformatics approach was applied to design twenty-one peptides consisting of in silico predicted linear B-cell and T-cell epitopes of aminopeptidase M24 from CD. These peptides were mapped for epitopes exploiting PEPSCAN procedure and using sera obtained from CD infected patients, umbilical cord blood, and healthy volunteers. Two new CD epitopes, ¹³¹KKGIK¹³⁵ and ¹⁸⁴KGTSTHVIT¹⁹², were identified and characterized. Immunoreactivity of the synthetic biotinylated ¹³¹KKGIK¹³⁵ epitope was significantly higher compared to ¹⁸⁴KGTSTHVIT¹⁹² epitope in Enzyme-Linked Immunosorbent Assay (ELISA) with umbilical cord blood and CDI patients' sera. Hereafter, the conjugate of bovine serum albumin and epitope ¹³¹KKGIK¹³⁵ was evaluated in vitro on lung epithelial cell line. In vitro, a significant induction of IL-6 by conjugate was observed, thereby we postulate that this new ¹³¹KKGIK¹³⁵ epitope possesses immunostimulating properties suggesting possibility of its use in a vaccine against Clostridioides difficile.

A novel vaccine candidate based on chimeric virus-like particle displaying multiple conserved epitope peptides induced neutralizing antibodies against EBV infection

Rationale: Epstein-Barr virus (EBV) is the causative pathogen for infectious mononucleosis and many kinds of malignancies including several lymphomas such as Hodgkin's lymphoma, Burkitt's lymphoma and NK/T cell lymphoma as well as carcinomas such as nasopharyngeal carcinoma (NPC) and EBV-associated gastric carcinoma (EBV-GC). However, to date no available prophylactic vaccine was launched to the market for clinical use.

Methods: To develop a novel vaccine candidate to prevent EBV infection and diseases, we designed chimeric virus-like particles (VLPs) based on the hepatitis B core antigen (HBc149). Various VLPs were engineered to present combinations of three peptides derived from the receptor binding domain of EBV gp350. All the chimeric virus-like particles were injected into Balb/C mice for immunogenicity evaluation. Neutralizing titer of mice sera were detected using an in vitro cell model.

Results: All chimeric HBc149 proteins self-assembled into VLPs with gp350 epitopes displayed on the surface of spherical particles. Interestingly, the different orders of the three epitopes in the chimeric proteins induced different immune responses in mice. Two constructs (149-3A and 149-3B) induced high serum titer against the receptor-binding domain of gp350. Most importantly, these two VLPs elicited neutralizing antibodies in immunized mice, which efficiently blocked EBV infection in cell culture. Competition analysis showed that sera from these mice contained antibodies to a major neutralizing epitope recognized by the strong neutralizing mAb 72A1.

Conclusion: Our data demonstrate that HBc149 chimeric VLPs provide a valuable platform to present EBV gp350 antigens and offer a robust basis for the development of peptide-based candidate vaccines against EBV.

Isolation and characterization of new human carrier peptides from two important vaccine immunogens

In the preparation of glycoconjugate vaccines in clinical practice, two highly immunogenic carrier proteins, CRM₁₉₇ and tetanus toxoid (TT), are predominantly conjugated with the capsular polysaccharides (CPSs) of bacterial pathogens. In addition, TT has long been used as an effective vaccine to prevent tetanus. While these carrier proteins play an important role in immunogenicity and vaccine design alike, their defined human major histocompatibility complex class II (MHCII) T cell epitopes are inadequately characterized. In this current work, we use mass spectrometry to identify the peptides from these carrier proteins that are naturally processed and presented by human B cells via MHCII pathway. The MHCII-presented peptides are screened for their T cell stimulation using primary CD4+ T cells from four healthy adult donors. These combined methods reveal a subset of eleven CD4+ T cell epitopes that proliferate and stimulate human T cells with diverse MHCII allelic repertoire. Six of these peptides stand out as potential immunodominant epitopes by responding in three or more donors. Additionally, we provide evidence of these natural epitopes eliciting more significant T cell responses in donors than previously published TT peptides selected from T cell epitope screening. This study serves toward understanding carrier protein immune responses and thus enables the use of these peptides in developing novel knowledge-based vaccines to combat persisting problems in glycoconjugate vaccine design.

Immunogenicity of synthetic peptide constructs based on PvMSP9E795-A808, a linear B-cell epitope of the P. vivax Merozoite Surface Protein-9

Plasmodium vivax Merozoite Surface Protein-9 (PvMSP-9) is a malaria vaccine candidate naturally immunogenic in humans and able to induce high antibody titers in animals when delivered as a recombinant protein. Recently, we identified the sequence EAAPENAEPVHENA (PvMSP9_E795-A808) as the main linear B-cell epitope in naturally exposed individuals. However, the potential of PvMSP9_E795-A808 as an immunogen in experimental animal models remained unexplored. Here we assess the immunogenicity of PvMSP9_E795-A808 using synthetic peptides. The peptides tested in BALB/c mice include two repeats of the sequence EAAPENAEPVHENA tested alone (peptide RII), or linked to an autologous (PvMSP9 peptide pL; pLRII) or heterologous (p2 tetanus toxin universal T cell epitope; TTRII) T cell epitope. Immune responses were evaluated by ELISA, FLUOROSPOT, and indirect immunofluorescence. We show that all of the peptide constructs tested were immunogenic eliciting specific IgG antibodies at different levels, with a prevalence of IgG1 and IgG2. Animals immunized with synthetic peptides containing T cell epitopes (pLRII or TTRII) had more efficient antibody responses that resulted in higher antibody titers able to recognize the native protein by immunofluorescence. Relevantly, the frequency of IFN-γ secreting SFC elicited by immunization with TTRII synthetic peptide was comparable to that reported to the PvMSP9-Nt recombinant protein. Taken together, our study indicates that PvMSP9_E795-A808 is highly immunogenic in mice and further studies to evaluate its value as promising vaccine target are warranted. Moreover, our study supports the critical role of CD4 T cell epitopes to enhance humoral responses induced by subunit based vaccines.

Perspective of Peptide Vaccine Composed of Epitope Peptide, CpG-DNA, and Liposome Complex Without Carriers

The magnitude and specificity of cell-mediated and humoral immunity are critically determined by peptide sequences; peptides corresponding to the B- or T-cell receptor epitopes are sufficient to induce an effective immune response if delivered properly. Therefore, studies on the screening and application of peptide-based epitopes have been done extensively for the development of therapeutic antibodies and prophylactic vaccines. However, the efficacy of immune response and antibody production by peptide-based immunization is too limited for human application at the present. To improve the efficacy of vaccines, researchers formulated adjuvants such as alum, water-in-oil emulsion, and Toll-like receptor agonists. They also employed liposomes as delivering vehicles to stimulate immune responses. Here, we review our recent studies providing a potent method of epitope screening and antibody production without conventional carriers. We adopted Lipoplex(O), comprising a natural phosphodiester bond CpG-DNA and a specific liposome complex, as an adjuvant. Lipoplex(O) induces potent stimulatory activity in humans as well as in mice, and immunization of mice with several peptides along with Lipoplex(O) without general carriers induces significant production of each peptide-specific IgG2a. Immunization of peptide vaccines against virus-associated antigens in mice has protective effects against the viral infection. A peptide vaccine against carcinoma-associated antigen and the peptide-specific monoclonal antibody has functional effects against cancer cells in mouse models. In conclusion, we improved the efficacy of peptide vaccines in mice. Our strategy can be applied in development of therapeutic antibodies or in defense against pandemic infectious diseases through rapid screening of potent B-cell epitopes.

Peptide Vaccine: Progress and Challenges

Conventional vaccine strategies have been highly efficacious for several decades in reducing mortality and morbidity due to infectious diseases. The bane of conventional vaccines, such as those that include whole organisms or large proteins, appear to be the inclusion of unnecessary antigenic load that, not only contributes little to the protective immune response, but complicates the situation by inducing allergenic and/or reactogenic responses. Peptide vaccines are an attractive alternative strategy that relies on usage of short peptide fragments to engineer the induction of highly targeted immune responses, consequently avoiding allergenic and/or reactogenic sequences. Conversely, peptide vaccines used in isolation are often weakly immunogenic and require particulate carriers for delivery and adjuvanting. In this article, we discuss the specific advantages and considerations in targeted induction of immune responses by peptide vaccines and progresses in the development of such vaccines against various diseases. Additionally, we also discuss the development of particulate carrier strategies and the inherent challenges with regard to safety when combining such technologies with peptide vaccines.

The use of self-adjuvanting nanofiber vaccines to elicit high-affinity B cell responses to peptide antigens without inflammation

Balancing immunogenicity with inflammation is a central tenet of vaccine design, especially for subunit vaccines that utilize traditional pro-inflammatory adjuvants. Here we report that by using a nanoparticulate peptide-based vaccine, immunogenicity and local inflammation could be decoupled. Self-assembled β-sheet-rich peptide nanofibers, previously shown to elicit potent antibody responses in mice, were found to be non-cytotoxic in vitro and, remarkably, elicited no measurable inflammation in vivo-with none of the swelling at the injection site, accumulation of inflammatory cells or cytokines, or production of allergic IgE that were elicited by an alum-adjuvanted vaccine. Nanofibers were internalized by dendritic cells and macrophages at the injection site, and only dendritic cells that acquired the material increased their expression of the activation markers CD80 and CD86. Immunization with epitope-bearing nanofibers elicited antigen-specific differentiation of T cells into T follicular helper cells and B cells into germinal center cells, as well as high-titer, high-affinity IgG that cross-reacted with the native protein antigen and was neutralizing in an in vitro influenza hemagglutination inhibition assay. These responses were superior to those induced by alum and comparable to those induced by complete Freund's adjuvant. Thus, nanoparticulate assemblies may provide a new route to non-inflammatory immunotherapies and vaccines.

Lipidated promiscuous peptides vaccine for tuberculosis-endemic regions

Despite nine decades of Bacillus Calmette--Guérin (BCG) vaccination, tuberculosis continues to be a major global health challenge. Clinical trials worldwide have proved the inadequacy of the BCG vaccine in preventing the manifestation of pulmonary tuberculosis in adults. Ironically, the efficacy of BCG is poorest in tuberculosis endemic areas. Factors such as nontuberculous or environmental mycobacteria and helminth infestation have been suggested to limit the efficacy of BCG. Hence, in high TB-burden countries, radically novel strategies of vaccination are urgently required. Here we showcase the properties of lipidated promiscuous peptide vaccines that target and activate cells of the innate and adaptive immune systems by employing a Toll-like receptor-2 agonist, S-[2,3-bis(palmitoyloxy)propyl]cysteine (Pam2Cys). Such a strategy elicits robust protection and enduring memory responses by type 1 T helper cells (Th1). Consequently, lipidated peptides may yield a better vaccine than BCG.

[Synthetic peptide vaccines]

This review considers the stages of the development of synthetic peptide vaccines against infectious agents, novel approaches and technologies employed in this process, including bioinformatics, genomics, proteomics, large-scale peptide synthesis, high-throughput screening methods, the use of transgenic animals for modelling human infections. An important role for the development and selection of efficient adjuvants for peptide immunogens is noted. Examples of synthetic peptide vaccine developments against three infectious diseases (malaria, hepatitis C, and foot-and-mouth disease) are given.

A modular approach to assembly of totally synthetic self-adjuvanting lipopeptide-based vaccines allows conformational epitope building

The technology described here allows the chemical synthesis of vaccines requiring correctly folded epitopes and that contain difficult or long peptide sequences. The final self-adjuvanting product promotes strong humoral and/or cell-mediated immunity. A module containing common components of the vaccine (T helper cell epitope and the adjuvanting lipid moiety S-[2,3-bis(palmitoyloxy)propyl]cysteine) was assembled to enable a plug and play approach to vaccine assembly. The inclusion within the module of a chemical group with chemical properties complementary and orthogonal to a chemical group present in the target epitope allowed chemoselective ligation of the two vaccine components. The heat-stable enterotoxin of enterotoxigenic Escherichia coli that requires strict conformational integrity for biological activity and the reproductive hormone luteinizing hormone-releasing hormone were used as the target epitopes for the antibody vaccines. An epitope from the acid polymerase of influenza virus was used to assemble a CD8(+) T cell vaccine. Evaluation of each vaccine candidate in animals demonstrated the feasibility of the approach and that the type of immune response required, viz. antibody or cytotoxic T lymphocyte, dictates the nature of the chemical linkage between the module and target epitope. The use of a thioether bond between the module and target epitope had little or no adverse effect on antibody responses, whereas the use of a disulfide bond between the module and target epitope almost completely abrogated the antibody response. In contrast, better cytotoxic T lymphocyte responses were obtained when a disulfide bond was used.

Synthetic peptide vaccines

This review considers the stages of the development of synthetic peptide vaccines against infectious agents, novel approaches and technologies employed in this process, including bioinformatics, genomics, proteomics, large-scale peptide synthesis, high-throughput screening methods, the use of transgenic animals for modelling human infections. An important role for the development and selection of efficient adjuvants for peptide immunogens is noted. Examples of synthetic peptide vaccine developments against three infectious diseases (malaria, hepatitis C, and foot-and-mouth disease) are given.

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.

CD8+ T cell adjuvant effects of Salmonella FliCd flagellin in live vaccine vectors or as purified protein

Salmonella flagellin, the flagellum structural subunit, has received particular interest as a vaccine adjuvant conferring enhanced immunogenity to soluble proteins or peptides, both for activation of antibody and cellular immune responses. In the present study, we evaluated the Salmonella enterica FliCd flagellin as a T cell vaccine adjuvant using as model the 9-mer (SYVPSAEQI) synthetic H2(d)-restricted CD8(+) T cell-specific epitope (CS(280-288)) derived from the Plasmodium yoelii circumsporozoite (CS) protein. The FliCd adjuvant effects were determined under two different conditions: (i) as recombinant flagella, expressed by orally delivered live S. Dublin vaccine strains expressing the target CS(280-288) peptide fused at the central hypervariable domain, and (ii) as purified protein in acellular vaccines in which flagellin was administered to mice either as a recombinant protein fused or admixed with the target CS(280-288) peptide. The results showed that CS(280-288)-specific cytotoxic CD8(+) T cells were primed when BALB/c mice were orally inoculated with the expressing the CS(280-288) epitope S. Dublin vaccine strain. In contrast, mice immunized with purified FliCd admixed with the CS(280-288) peptide and, to a lesser extent, fused with the target peptide developed specific cytotoxic CD8(+) T cell responses without the need of a heterologous booster immunization. The CD8(+) T cell adjuvant effects of flagellin, either fused or not with the target peptide, correlated with the in vivo activation of CD11c(+) dendritic cells. Taken together, the present results demonstrate that Salmonella flagellins are flexible adjuvant and induce adaptative immune responses when administered by different routes or vaccine formulations.

Developing vaccines against minor capsid antigen L2 to prevent papillomavirus infection

A subset of human papillomavirus (HPV) genotypes is responsible for approximately 5% of all cancer deaths globally, and uterine cervical carcinoma accounts for the majority of these cases. The impact of HPV is greatest for women who do not have access to effective secondary preventive measures, and consequently over 80% of cervical cancer deaths worldwide occur in developing nations. The understanding that persistent infection by this 'oncogenic' subset of HPV genotypes is necessary for the development of cervical carcinoma has driven the development of preventive vaccines. Two preventive vaccines comprising recombinant HPV L1 virus-like particles (VLPs) have been licensed. However, the current cost of these vaccines precludes sustained global delivery, and they target only two of the approximately 15 known oncogenic HPV types, although approximately 70% of cervical cancer cases are attributed to these two types and there is evidence for some degree of cross-protection against other closely related types. A possible approach to broader immunity at lower cost is to consider vaccination against L2. L2 vaccines can be produced inexpensively and they also have the promise of conferring much broader cross-type protective immunity than that observed with L1 VLP immunization. However, L2 vaccine development lags behind L1 VLP vaccines and several technical hurdles remain.

The caveolin-1 binding domain of HIV-1 glycoprotein gp41 (CBD1) contains several overlapping neutralizing epitopes

The CBD1 peptide (SLEQIWNNMTWMQWDK), corresponding to the consensus caveolin-1 binding domain in HIV-1 envelope glycoprotein gp41 (CBD1), elicits the production of antibodies that inhibit infection of primary CD4(+) T lymphocytes by various primary HIV-1 isolates. Here we show that HIV-neutralizing antibodies against CBD1 react with multiple conformational epitopes that overlap the highly conserved caveolin-1 binding motif (CBM) with the N-terminal conserved isoleucine residue. The CBM-based peptides IWNNMTWMQW and IWNNMTW when fused to a T helper epitope are immunogenic by inducing high titer CBM-specific antibodies capable of neutralizing HIV-1 infection in primary T lymphocyte cultures. Interestingly, neutralizing immune sera raised against a given peptide do not cross-react with related CBM-derived peptides, thus suggesting the existence of distinct neutralizing epitopes that probably reflect the dynamic conformational features of CBD1. In accord with this, the mixture of neutralizing immune sera raised against several CBM-derived peptides exerts a synergistic neutralizing activity against HIV-1 infection. Finally, the existence of several distinct overlapping epitopes in CBD1 is confirmed by murine monoclonal antibodies that we generated against the CBM-derived chimeric peptides. Our results indicate that CBD1- and CBM-based peptides mimic distinct dynamic conformations of CBD1, and thus such peptides could provide specific immunogens for an efficient vaccine preparation against HIV/AIDS infection.

The CBD1 peptide corresponding to the caveolin-1 binding domain of HIV-1 glycoprotein gp41 elicits neutralizing antibodies in cynomolgus macaques when administered with the tetanus T helper epitope

CBD1 peptide (SLEQIWNNMTWMQWDK), corresponding to the consensus caveolin-1 binding domain in HIV-1 envelope glycoprotein gp41, elicits the production of antibodies that inhibit infection of primary CD4(+) T lymphocytes by various primary HIV-1 isolates. Here the immunogenicity of the CBD1 peptide was investigated in cynomolgus macaques using adjuvants that are acceptable for human use. In the first set of studies, macaques were immunized with the CBD1 peptide in association with muramyl dipeptide derivative MDP-Lys(L18) combined with the oil-in-water emulsion, MF-59. After five immunizations at 4 weeks interval, the antibody titer against the CBD1 peptide was found to be either medium, poor, weak or none, thus suggesting that the CBD1 immune response might be restricted by the major histocompatibility complex (MHC) class II molecules. In the second set of studies therefore, macaques were immunized with the CBD1 peptide in association with the 'promiscuous' T cell epitope from the tetanus toxin, either as free peptides or covalently linked with the dilysine linker using CpG ODN and Montanide ISA 51 as adjuvants. This latter immunization procedure boosted markedly the anti-CBD1 antibody response, since even the non-responders generated high-titered peptide-specific antibodies. Moreover, co-immunization of the CBD1 and the T helper epitope as free peptides seemed to be favorable for the production of neutralizing antibodies, with 50% inhibition of HIV-1 infection occurring at 300-400-fold dilution of the immune sera. Finally, neutralizing and non-neutralizing immune macaque sera could be differentiated by the profile of cross-reactivity with overlapping CBD1-related peptides in ELISA. Taken together, our results demonstrate that the CBD1 peptide is immunogenic in macaques and that an eventual MHC-restriction could be overcome by the administration with an appropriate T helper epitope.

Protection against heterologous human papillomavirus challenge by a synthetic lipopeptide vaccine containing a broadly cross-neutralizing epitope of L2

Persistent infection with the high-risk subset of genitotropic human papillomavirus (HPV) genotypes is a necessary cause of cervical cancer. Given the global burden of cervical cancer, a low-cost, broadly protective vaccine is needed. RG-1 is a cross-neutralizing and protective monoclonal antibody that recognizes residues 17-36 of HPV16 minor capsid protein L2. Because this epitope is highly conserved in divergent HPV types, we determined whether vaccination with HPV16 L2 17-36 peptide is broadly protective. The peptide was administered to BALB/c mice three times at monthly intervals, either alone or in the context of a synthetic lipopeptide vaccine candidate (P25-P2C-HPV) produced by linkage of the HPV peptide with a broadly recognized T helper epitope (P25) and the Toll-like receptor-2 (TLR2) ligand dipalmitoyl-S-glyceryl cysteine (P2C). In contrast to vaccination with the L2 17-36 peptide or P25-P2C alone, a potent L2-specific antibody response was generated to the P25-P2C-HPV lipopeptide when delivered either s.c. or intranasally. Sera from mice vaccinated with the P25-P2C-HPV lipopeptide neutralized not only HPV16 pseudovirions but also other evolutionarily divergent oncogenic genital (HPV18, HPV45) and cutaneous (HPV5, BPV1) types. The L2-specific antibody response depended on MHC class II, CD40, and MyD88 signaling. Additionally, vaccination with the P25-P2C-HPV lipopeptide protected mice from homologous challenge with HPV16 pseudovirions at cutaneous and genital sites and heterologous challenge with HPV45 pseudovirions. If provided in the appropriate context, therefore, HPV16 L2 17-36 might be used in a totally synthetic cross-protective HPV vaccine.

Development of a novel antimicrobial peptide, AG-30, with angiogenic properties

The utility of various synthetic peptides has been investigated in clinical trials of the treatment of cancers, infectious diseases and endocrine diseases. In the process of functional gene screening with in silico analysis for molecules with angiogenic properties, we generated a small peptide, angiogenic peptide (AG)-30, that possesses both antimicrobial and pro-inflammatory activities. AG-30 has an α-helix structure with a number of hydrophobic or net positively charged amino acids and a propensity to fold into amphipathic structures. Indeed, AG-30 exhibited antimicrobial activity against various bacteria, induced vascular endothelial cell growth and tube formation in a dose-dependent manner and increased neovascularization in a Matrigel plug assay. As a result, AG-30 up-regulated expression of angiogenesis-related cytokines and growth factors for up to 72 hrs in human aortic endothelial cells. To further evaluate the angiogenic effect of AG-30 in vivo, we developed a slow-release AG-30 system utilizing biodegradable gelatin microspheres. In the ischaemic mouse hind limb, slow-release AG-30 treatment results in an increase in angiogenic score, an increase in blood flow (as demonstrated by laser Doppler imaging) and an increase in capillary density (as demonstrated by immunostaining with anti-CD31 antibody). These data suggest that the novel peptide, AG-30, may have therapeutic potential for ischaemic diseases.

Construction and characterization of a recombinant fowlpox virus containing HIV-1 multi-epitope-p24 chimeric gene in mice

The epidemic of HIV/AIDS is sweeping across the world. It is of great importance to figure out new ways to curb this disease. Epitope-based vaccine is one of these solutions. In this study, a chimeric gene was obtained by combination of a designed HIV-1 multi-epitope gene (MEG) and HIV-1 p24 gene. A recombinant plasmid pUTA2-MEGp24 was then constructed by inserting MEGp24 gene into the downstream of the promoter (ATI-P7.5x20) of fowlpox virus (FPV) transfer vector pUTA2. The recombinant plasmid and wild-type FPV 282E4 strain were then co-transfected into CEF cells and homologous recombination occurred. A recombinant virus expressing HIV-1 protein MEGp24 was screened by genome PCR and Western blot assay. Large scale preparation and purification of the recombinant fowlpox virus (rFPV) were then carried out. BALB/c mice were immunized intramuscularly with the rFPV for three times on day 0, 14 and 42. Mice were executed and sampled one week after the third inoculation. Anti-HIV-1 antibody in serum and Th1 cytokines in the supernatant of cultured spleen cells were assayed by ELISA. The count of T lymphocyte subsets and the CTL activity of spleen lymphocytes were analyzed by flow cytometry and lactate dehydrogenase (LDH) release assay, respectively. The results showed that HIV-1 specific antibody in serum and increased T lymphocyte subsets (CD4(+) T, CD8(+) T) were detected in the immunization group. CTL target-killing activity and higher secretion of Th1 cytokines (IFN-gamma and IL-2) of spleen lymphocytes stimulated by H-2(d)-restricted CTL peptide were observed in immunized mice. We concluded that the rFPV may induce HIV-1 specific immunity especially cellular immunity in mice.

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.

Synthetic peptide vaccination in cattle: induction of strong cellular immune responses against peptides derived from the Mycobacterium bovis antigen Rv3019c

Fully synthetic peptide vaccines possess attractive cost and safety attributes. However, peptide vaccines that induce cell-mediated immunity require both selection of appropriate peptides and the development of adjuvant formulations supporting the induction of cellular immunity. An adjuvant formulation composed of emulsigen and the synthetic CpG motif containing ODN2007 was tested in cattle for its ability to induce cellular immunity after peptide vaccination, and compared to Rv3019c DNA vaccination. Peptides from the protective Mycobacterium bovis antigen Rv3019c were included into the vaccine on the basis of their frequent and strong recognition by T cells from M. bovis infected or BCG vaccinated cattle. Following peptide vaccination, strong IFN-gamma and proliferative T cell responses were observed. Proliferative, but no significant IFN-gamma responses were induced by DNA vaccination. Peptide vaccination boosted responses primed by DNA vaccination. In conclusion, emulsigen and CpG motif containing ODN constitute a promising adjuvant formulation to deliver peptides to veterinary species.

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.

Non-clinical safety evaluation of novel vaccines and adjuvants: new products, new strategies

Advances in molecular biology and biotechnology, coupled with an increased understanding of disease processes and mechanisms of protective immunity have facilitated the development of new rationally-designed vaccines utilising recombinant proteins, naked DNA, live vectors, genetically-modified toxins and whole dendritic and tumour cells for both prophylaxis and therapy of a wide range of indications. These new vaccine technologies coupled with novel adjuvants, delivery systems, formulations, dosing routes and regimes present many unique and difficult challenges in demonstrating product safety and efficacy to support clinical testing. This paper aims to review these novel vaccine and adjuvant technologies and to highlight the key safety issues potentially associated with them. Approaches taken to demonstrate vaccine safety by assessing systemic and local toxicity, biodistribution and persistence, immunogenicity and immunotoxicity, reproductive toxicology, safety pharmacology and genotoxicity within the current regulatory framework are presented.

RGDS peptide inhibits activation of lymphocytes and adhesion of activated lymphocytes to human umbilical vein endothelial cells in vitro

The Arg-Gly-Asp (RGD) motif is known to mediate cell adhesion to several extracellular matrix components as well as cell-cell interactions. In the present study, we investigated whether the RGDS peptide interferes with cell-cell recognition-based events such as allogeneic activation of PBMC and PBMC adhesion to human umbilical vein endothelial cells (HUVEC). We show here for the first time, to our knowledge, that RGDS significantly inhibits adhesion of activated PBMC to HUVEC; in addition, RGDS inhibits PBMC allogenenic activation in human mixed lymphocyte reaction assays. Caspases played a pivotal role in both events, because preventing their activation abolished or strongly reduced the observed inhibitory effect. The RGDS antirecognition effect was strongly increased by pretreatment of HUVEC with RGDS, which affected mostly T lymphocyte adhesion to HUVEC. These results indicate that PBMC allogeneic activation, as well as reciprocal recognition between activated PBMC and endothelial cells, are RGDS-dependent events that occur through a dual effect involving anti-adhesive and caspase-dependent mechanisms. These data suggest a potential role of RGDS in cell-mediated immunity, inflammation and organ transplantation.

Preclinical safety testing of biotechnology-derived pharmaceuticals: understanding the issues and addressing the challenges

The unique and complex nature of biotechnology-derived pharmaceuticals has meant that it is often not possible to follow the conventional safety testing programs used for chemicals, and hence they are evaluated on a case-by-case basis. Nonclinical safety testing programs must be rationally designed with a strong scientific understanding of the product, including its method of manufacture, purity, sequence, structure, species specificity, pharmacological and immunological effects, and intended clinical use. This knowledge, coupled with a firm understanding of the regulatory requirements for particular product types, will ensure that the most sensitive and regulatory-compliant test systems are used to optimize the chances of gaining regulatory approval for clinical testing or marketing authorization in the shortest possible time frame.

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.

Successful identification of novel agents to control infectious diseases from screening mixture-based peptide combinatorial libraries in complex cell-based bioassays

Mixture-based peptide synthetic combinatorial libraries (SCLs) represent a valuable source for the development of novel agents to control infectious diseases. Indeed, a number of studies have now proven the ability of identifying active peptides from libraries composed of thousands to millions of peptides in cell-based biosystems of varying complexity. Furthermore, progressing knowledge on the importance of endogenous peptides in various immune responses lead to a regain in importance for peptides as potential therapeutic agents. This article is aimed at providing recent studies in our laboratory for the development of antimicrobial or antiviral peptides derived from mixture-based SCLs using cell-based assays, as well as a short review of the importance of such peptides in the control of infectious diseases. Furthermore, the use of positional scanning (PS) SCL-based biometrical analyses for the identification of native optimal epitopes specific to HIV-1 proteins is also presented.

Novel strategy for identification of candidate cytotoxic T-cell epitopes from human preproinsulin

We describe a strategy for identifying ligands of human leukocyte antigen (HLA) class I molecules based on a peptide library-mediated in vitro assembly of recombinant class I molecules. We established a microscale class I assembly assay and used a capture ELISA to quantify the assembled HLA-peptide complexes. The identity of the bound ligands was then deduced by mass spectrometry. In this method, HLA complexes assembled in vitro in the presence of components of a mixture of peptides were immunoprecipitated and the bound peptide(s) identified by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. This process of epitope extraction is robust and can be used with complex mixtures containing in excess of 300 candidate ligands. A library of overlapping peptides representing all potential octamers, nonamers and decamers from human preproinsulin was synthesized using unique library chemistry. Peptides from the library were used to initiate assembly of recombinant HLA-B8, HLA-B15 and HLA-A2, facilitating the identification of candidate T-cell epitopes from preproinsulin.

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.