The influence of orientation and number of copies of T and B cell epitopes on the specificity and affinity of antibodies induced by chimeric peptides

Identification of potential candidate vaccines against Mycobacterium ulcerans based on the major facilitator superfamily transporter protein

Buruli ulcer is a neglected tropical disease that is characterized by non-fatal lesion development. The causative agent is Mycobacterium ulcerans (M. ulcerans). There are no known vectors or transmission methods, preventing the development of control methods. There are effective diagnostic techniques and treatment routines; however, several socioeconomic factors may limit patients' abilities to receive these treatments. The Bacillus Calmette-Guérin vaccine developed against tuberculosis has shown limited efficacy, and no conventionally designed vaccines have passed clinical trials. This study aimed to generate a multi-epitope vaccine against M. ulcerans from the major facilitator superfamily transporter protein using an immunoinformatics approach. Twelve M. ulcerans genome assemblies were analyzed, resulting in the identification of 11 CD8+ and 7 CD4+ T-cell epitopes and 2 B-cell epitopes. These conserved epitopes were computationally predicted to be antigenic, immunogenic, non-allergenic, and non-toxic. The CD4+ T-cell epitopes were capable of inducing interferon-gamma and interleukin-4. They successfully bound to their respective human leukocyte antigens alleles in in silico docking studies. The expected global population coverage of the T-cell epitopes and their restricted human leukocyte antigens alleles was 99.90%. The population coverage of endemic regions ranged from 99.99% (Papua New Guinea) to 21.81% (Liberia). Two vaccine constructs were generated using the Toll-like receptors 2 and 4 agonists, LprG and RpfE, respectively. Both constructs were antigenic, non-allergenic, non-toxic, thermostable, basic, and hydrophilic. The DNA sequences of the vaccine constructs underwent optimization and were successfully in-silico cloned with the pET-28a(+) plasmid. The vaccine constructs were successfully docked to their respective toll-like receptors. Molecular dynamics simulations were carried out to analyze the binding interactions within the complex. The generated binding energies indicate the stability of both complexes. The constructs generated in this study display severable favorable properties, with construct one displaying a greater range of favorable properties. However, further analysis and laboratory validation are required.

Recombinant KRAS G12D Protein Vaccines Elicit Significant Anti-Tumor Effects in Mouse CT26 Tumor Models

Drug development targeting the most frequently mutation G12D of KRAS has great significance. As an attractive immunotherapy, cancer vaccines can overcome binding difficulties of small molecules; however, the weak immunogenicity and production difficulties of reported KRAS mutation vaccines limit their clinical application. To improve antigen-specific immune responses and Anti-Tumor effects on tumors expressing KRAS G12D mutation, we designed recombinant proteins containing KRAS peptide (amino acids 5–21) with G12D (called SP) in two forms: DTT-SP₄ and DTSP. DTT-SP₄ was constructed by fusing four copies of SP to the C-terminal of the translocation domain of diphtheria toxin (DTT), and DTSP was constructed by grafting SP onto DTT. The two vaccines in combination with aluminum hydroxide (Alum) and cytosine phosphoguanine (CpG) successfully induced conspicuous SP-specific humoral and cellular immune responses, and displayed prominent protective and therapeutic Anti-Tumor effects in mouse CT26 tumor models. Surprisingly, the DTSP-treated group displayed better Anti-Tumor effects in vivo compared with the DTT-SP₄-treated and control groups. Moreover, 87.5 and 50% of DTSP-treated mice in the preventive and therapeutic models were tumor free, respectively. Notably, in the DTSP-treated group, the interferon-γ (IFN-γ) expression of T cells in vitro and the T-helper 1 (Th1)–related cytokine expression in tumor tissues indicated that the activated Th1 immune response may be involved in Anti-Tumor activity. Furthermore, DTSP treatment remarkably altered the subpopulation of T cells in splenocytes and tumor-infiltrating lymphocytes. The percentage of effector CD8⁺ T cells increased, whereas that of immunosuppressive CD4⁺Foxp3⁺ T cells remained reduced in the DTSP group. Dramatic tumor-inhibitory effects of DTSP, which is easily prepared, make it a more attractive strategy against KRAS G12D tumors.

Promiscuous T cell epitopes boosts specific IgM immune response against a P0 peptide antigen from sea lice in different teleost species

The development of vaccines employing conserved protein antigens, for instance ribosomal protein P0, has as disadvantage the high degree of identity between pathogen and host proteins due to possible induction of tolerance or auto antibodies in the host organism. To overcome this drawback, peptide-based vaccines have been designed with a proved high efficacy. The use of defined peptides as antigens has the problem that they are generally poor immunogenic unless coupled to a carrier protein. Several studies have established the potential for promiscuous T cell epitopes incorporated into chimeric peptides to enhance the immunogenicity in mammals. On the contrary, studies about the role of these epitopes on teleost immune system are scarce. Therefore, the main objective of our present study was to evaluate the potential of promiscuous T cell epitopes to boost specific IgM immune response in teleost fish against a peptide antigen. With this aim, we used a peptide of 35 amino acids from the ribosomal P0 protein of Lepeophtheirus salmonis, an important parasite in salmon aquaculture. We fused this peptide to the C-terminal of T cell epitopes from tetanus toxin and measles virus and produced the chimeric protein in Escherichia coli. Following vaccination, IgM antibody production was monitored in different immunization schemes in Tilapia, African catfish and Atlantic salmon. The results demonstrated for first time that the addition of T cell epitopes at the N-terminal of a target peptide increased IgM specific response in different teleost species, revealing the potential of this approach to develop peptide-based vaccines for aquaculture. The results are also of great importance in the context of vaccine development against sea lice using ribosomal protein P0 as antigen taking into account the key role of P0 in protein synthesis and other essential physiological processes.

Vaccination with a Paramyosin-Based Multi-Epitope Vaccine Elicits Significant Protective Immunity against Trichinella spiralis Infection in Mice

Trichinellosis is a worldwide zoonosis and remains a serious public health problem. Interrupting parasite transmission via vaccination of livestocks with a potent vaccine is a practical approach to prevent human Trichinellosis. Our previous studies have identified that paramyosin of Trichinella spiralis (Ts-Pmy) is a good vaccine candidate against Trichinellosis. In this study, a novel multi-epitope vaccine (MEP) was constructed by using four CD4⁺ T cell epitopes (P2, P3, P4, and P5) and one B cell epitope (YX1) from Ts-Pmy and expressed as a soluble recombinant protein (rMEP) in Escherichia coli. Mice immunized with rMEP vaccine produced significant higher muscle larval reduction (55.4%) than that induced by immunization of parental rTs-Pmy (34.4%) against T. spiralis infection. The better protection is associated with rMEP induced high levels of anti-rMEP specific IgG and subclass IgG1/IgG2a, elevated T cell proliferation of splenocytes and secretion of IFN-γ, IL-4 and IL-5. The cellular response to individual T cell epitope also showed that splenocytes from mice immunized with rMEP strongly response to the stimulation of synthetic epitope peptide P2, P3, and P4, but not to P5, suggesting that most of T cell epitopes are exposed and processed well during immunization that may contribute to the high protection induced by the immunization of rMEP. This study implies that epitope vaccine is a promising approach for the development of vaccines against Trichinellosis.

Immune-tolerant elastin-like polypeptides (iTEPs) and their application as CTL vaccine carriers

BACKGROUND

Cytotoxic T lymphocyte (CTL) vaccine carriers are known to enhance the efficacy of vaccines, but a search for more effective carriers is warranted. Elastin-like polypeptides (ELPs) have been examined for many medical applications but not as CTL vaccine carriers.

PURPOSE

We aimed to create immune tolerant ELPs using a new polypeptide engineering practice and create CTL vaccine carriers using the ELPs.

RESULTS

Four sets of novel ELPs, termed immune-tolerant elastin-like polypeptide (iTEP) were generated according to the principles dictating humoral immunogenicity of polypeptides and phase transition property of ELPs. The iTEPs were non-immunogenic in mice. Their phase transition feature was confirmed through a turbidity assay. An iTEP nanoparticle (NP) was assembled from an amphiphilic iTEP copolymer plus a CTL peptide vaccine, SIINFEKL. The NP facilitated the presentation of the vaccine by dendritic cells (DCs) and enhanced vaccine-induced CTL responses.

DISCUSSION

A new ELP design and development practice was established. The non-canonical motif and the immune tolerant nature of the iTEPs broaden our insights about ELPs. ELPs, for the first time, were successfully used as carriers for CTL vaccines.

CONCLUSION

It is feasible to concurrently engineer both immune-tolerant and functional peptide materials. ELPs are a promising type of CTL vaccine carriers.

Tandem truncated rotavirus VP8* subunit protein with T cell epitope as non-replicating parenteral vaccine is highly immunogenic

The two currently available live oral rotavirus vaccines, Rotarix(®) and RotaTeq(®), are highly efficacious in the developed countries. However, the efficacy of such vaccines in resource deprived countries in Africa and Southeast Asia is low. We reported previously that a bacterially-expressed rotavirus P2-P[8] ΔVP8* subunit vaccine candidate administered intramuscularly elicited high-titers of neutralizing antibodies in guinea pigs and mice and significantly shortened the duration of diarrhea in neonatal gnotobiotic pigs upon oral challenge with virulent human rotavirus Wa strain. To further improve its vaccine potential and provide wider coverage against rotavirus strains of global and regional epidemiologic importance, we constructed 2 tandem recombinant VP8* proteins, P2-P[8] ΔVP8*-P[8] ΔVP8* and P2-P[8] ΔVP8*-P[6] ΔVP8* based on Escherichia coli expression system. The two resulting recombinant tandem proteins were highly soluble and P2-P[8] ΔVP8*-P[8] ΔVP8* was generated with high yield. Moreover, guinea pigs immunized intramuscularly by 3 doses of the P2-P[8] ΔVP8*-P[8] ΔVP8* or P2-P[8] ΔVP8*-P[6] ΔVP8* vaccine with aluminum phosphate adjuvant developed high titers of homotypic and heterotypic neutralizing antibodies against human rotaviruses bearing G1-G4, G8, G9 and G12 with P[8], P[4] or P[6] combination. The results suggest that these 2 subunit vaccines in monovalent or bivalent formulation can provide antigenic coverage to almost all the rotavirus G (VP7) types and major P (VP4) types of global as well as regional epidemiologic importance.

Multiple antigen peptide consisting of B- and T-cell epitopes of F1 antigen of Y. pestis showed enhanced humoral and mucosal immune response in different strains of mice

Yersinia pestis is a causative agent of plague. F1 and V antigen based vaccines have shown remarkable protection in experimental animals. In order to develop epitope based immunogen, three B and one T-cell epitopes of F1 antigen with palmitate residue at amino terminal were assembled on a lysine backbone as multiple antigen peptide (MAP or F1-MAP). MAP was characterized by SDS-PAGE, immunoblot and immunoreactivity with anti F1 sera. MAP was entrapped in PLGA (polylactide-co-glycolide) microparticles and humoral, mucosal immune responses were studied after intranasal immunization with/without CpG ODN 1826 (CpG)/murabutide in different strains of mice. Serum and mucosal washes were measured for MAP specific IgG, IgA, sIgA and IgG subclasses in three strains of mice. F1-MAP showed high serum antibody and mucosal IgG and IgA peak antibody titers. MAP with CpG showed significantly high (p<0.001) peak antibody titer ranging from 102,400 to 204,800 for IgG and 6400 to 12,800 for IgA. High mucosal sIgA and its secretary component detection confirmed generation of mucosal response in intestinal and lung washes. MAP antisera also showed significant immunoreactivity with individual peptides. Moreover, antibody specific activity (IgG, IgA and sIgA) positively correlates with peak antibody titers. Predominantly IgG2a/IgG2b subclass was observed with CpG formulation but in other formulation a mixed IgG1 and IgG2a response was observed. The present study highlights the importance of multiple antigen peptide approach of F1-antigen with CpG as an alternative approach for subunit vaccine.

Immunogenic comparison for two different recombinant chimeric peptides (CP12 and CP22) containing one or two copies of three linear B cell epitopes from β-hCG subunit

To develop a superior chimeric peptide (CP) vaccine of human chorionic gonadotropin (hCG), two CP antigens (named CP12 and CP22) encoding one or two copies of three linear B cell epitopes from the β-hCG subunit and six foreign T cell epitopes, including two promiscuous TCEs from hepatitis B surface antigen and tetanus toxoid, were constructed and biosynthesized. The hCG CP12 and CP22 of 21 or 23 kDa, respectively, were expressed in Escherichia coli at the level of ~1% of total cell proteins when inserted into thermo-inducible pBV221 expression vector. The purified CP12 and CP22 proteins with >95% relative homogeneity are immunogenic, and elicited antibodies against the β5, β9 and β8 BCEs of β-hCG in both rabbits and three different inbred strains of mice. A mouse uterine weight study in Balb/c mice demonstrated that the CP12 and CP22 antigens with an additional β5 neutralizing epitope enhanced the in vivo bio-neutralization capacity of the induced antibodies compared to the C-terminal immunogen of β-hCG. We propose that the biosynthesized CP22, possessing with two copies of three BCEs, represents a novel candidate antigen for an hCG contraceptive or tumor therapeutic vaccine.

Identification and characterization of dominant helper T-cell epitopes in the nucleocapsid protein of severe acute respiratory syndrome coronavirus

By using a series of overlapping synthetic peptides covering 98% of the amino acid sequence of the nucleocapsid protein (NP) of severe acute respiratory syndrome coronavirus (SARS-CoV), four helper T-cell (Th) epitopes (NP11, residues 11 to 25; NP51, residues 51 to 65; NP61, residues 61 to 75; and NP111, residues 111 to 125) in C57BL mice (H-2(b)), four (NP21, residues 21 to 35; NP91, residues 91 to 105; NP331, residues 331 to 345; and NP351, residues 351 to 365) in C3H mice (H-2(k)), and two (NP81, residues 81 to 95; and NP351, residues 351 to 365) in BALB/c mice (H-2(d)) have been identified. All of these peptides were able to stimulate the proliferation of NP-specific T-cell lines or freshly isolated lymph node cells from mice immunized with recombinant NP. Immunization of mice with synthetic peptides containing appropriate Th epitopes elicited strong cellular immunity in vivo, as evidenced by delayed-type hypersensitivity. Priming with the helper peptides (e.g., NP111 and NP351) significantly accelerated the immune response induced by recombinant NP, as determined by the production of NP-specific antibodies. When fused with a conserved neutralizing epitope (SP1143-1157) from the spike protein of SARS-CoV, NP111 and NP351 assisted in the production of high-titer neutralizing antibodies in vivo. These data provide useful insights regarding immunity against SARS-CoV and have the potential to help guide the design of peptide-based vaccines.

Tandem copies of a human rotavirus VP8 epitope can induce specific neutralizing antibodies in BALB/c mice

The VP8 subunit protein of human rotavirus (HRV) plays an important role in viral infectivity and neutralization. Recombinant peptide antigens displaying the amino acid sequence M(1)ASLIYRQLL(10), a linear neutralization epitope on the VP8 protein, were constructed and examined for their ability to generate anti-peptide antibodies and HRV-neutralizing antibodies in BALB/c mice. Peptide antigen constructs were expressed in E. coli as fusion proteins with thioredoxin and a universal tetanus toxin T-cell epitope (P2), in order to enhance the anti-peptide immune response. The peptide antigen containing three tandem copies of the VP8 epitope induced significantly higher levels of anti-peptide antibody than only a single copy of the epitope, or the peptide co-administered with the carrier protein and T-cell epitope. Furthermore, the peptide antigen containing three copies of the peptide produced significantly higher virus-neutralization titres, higher than VP8, indicating that a peptide antigen displaying repeating copies of the amino acid region 1-10 of VP8 is a more potent inducer of HRV-neutralizing antibodies than VP8 alone, and may be useful for the production of specific neutralizing antibodies for passive immunotherapy of HRV infection.

Enhanced immunogenicity of a functional enzyme by T cell epitope modification

BACKGROUND

T helper epitopes are necessary for the induction of high titers of antigen-specific IgG antibodies. We are interested in the epitope modification of intact proteins as a method to enhance their immunogenicity for the generation of recombinant protein-based vaccines.

RESULTS

Hartley strain guinea pig T cell epitopes were mapped for two related bacterial proteases. Two T cell epitopes were found in one of the proteases, while a comparatively reduced immunogenicity protease had no detectable T cell epitopes. A T cell epitope sequence homologous to the immunogenic protease was created in the less immunogenic protease by changing a single amino acid. Proliferative responses to the whole protein parent enzyme were two-fold higher in splenocyte cultures from variant-immunized animals. We found that the single amino acid change in the variant resulted in a protein immunogen that induced higher titers of antigen-specific IgG antibody at low doses and at early time points during the immunization protocol. The serum from parent- and variant-immunized guinea pigs cross-reacted at both the protein and the peptide level. Finally, animals primed to the variant but boosted with the parent enzyme had higher levels of antigen-specific IgG than animals immunized with the parent enzyme alone.

CONCLUSIONS

With a single amino acid change we have introduced a T cell epitope into a comparatively low-immunogenic enzyme and have increased its immunogenicity while retaining the enzyme's original proteolytic function. The ability to immunomodulate proteins while leaving their function intact has important implication for the development of recombinant vaccines and protein-based therapeutics.

Mapping antigenic sites of an immunodominant surface lipoprotein of Mycoplasma agalactiae, AvgC, with the use of synthetic peptides

As a first step toward the design of an epitope vaccine to prevent contagious agalactia, the strongly immunogenic 55-kDa protein of Mycoplasma agalactiae was studied and found to correspond to the AvgC protein encoded by the avgC gene. The avg genes of M. agalactiae, which encode four variable surface lipoproteins, display a significant homology to the vsp (variable membrane surface lipoproteins) genes of the bovine pathogen Mycoplasma bovis at their promoter region as well as their N-terminus-encoding regions. Some members of the Vsp family are known to be involved in cytoadhesion to host cells. In order to localize immunogenic peptides in the AvgC antigen, the protein sequence was submitted to epitope prediction analysis, and five sets of overlapping peptides, corresponding to five selected regions, were synthesized by Spot synthesis. Reactive peptides were selected by immunobinding assay with sera from infected sheep. The three most immunogenic epitopes were shown to be surface exposed by immunoprecipitation assays, and one of these was specifically recognized by all tested sera. Our study indicates that selected epitopes of the AvgC lipoprotein may be used to develop a peptide-based vaccine which is effective against M. agalactiae infection.

Impact of epitope permutations in the antibody response of mice to a multi-epitope polypeptide of the V3 loop of human immunodeficiency virus type 1

Our group have produced in Escherichia coli and evaluated the immunogenicity of different multi-epitope polypeptides (MEPs) bearing one copy of V3 loop sequential B cell epitopes from several isolates of human immunodeficiency virus type 1 (HIV-1) gp120. One of these MEPs called TAB9 comprises the 15 central amino acids of the V3 loop from isolates LR150, JY1, RF, MN, BRVA and IIIB in this order. Antibodies against all V3 regions were elicited after immunization of rabbits, macaques and humans with TAB9. In contrast, mice immunized with this protein only developed antibodies against epitopes JY1, LR150 and MN in that order (JY1>LR150>MN>>>RF, BRVA, IIIB) resembling an immunodominant gradient from the N-terminus to the C-terminal portion of this construction. To assess what role the location of the V3 epitopes in TAB9 could play, we constructed the protein TAB16, by altering the position of V3 epitopes in TAB9 primary structure and compared the pattern of antibodies elicited by both MEPs in H-2(d) Balb/c mice. The MEP TAB16 elicited antibody titers comparable to that of the sera from mice immunized with TAB9. There were no statistical differences in antibody titers between both groups (P>0.05). JY1, LR150 and MN V3 epitopes were again immunodominant in mice immunized with TAB16 fusion protein. The highest antibody titers detected in both groups among V3 epitopes corresponded to JY1, now located at the C-terminus of the permuted chimera. Antibodies against V3 epitopes RF, BRVA and IIIB were again not detected. Additionally, the MN V3 epitope showed to be significantly more immunogenic in its new orientation in TAB16, possibly as a result of a higher degree of accessibility in the surface of the protein. The results of the present investigation strongly suggest that the sequential order or the intramolecular position of V3 epitopes inside the primary structure of TAB9 and TAB16 MEPs does not interfere with the global immunogenicity or with the hierarchy of immunodominance of these regions.

Nasal delivery of epitope based vaccines

Essentially all of the currently available vaccines are based on the use of inactivated or live-attenuated pathogens. However, these vaccines have several shortcomings, such as difficulties of in vitro culturing, biohazard risks, as well as loss of efficacy due to the genetic variations seen in many viruses. These problems may potentially be solved by immunising with epitope-based vaccines consisting of rationally designed protective epitopes, appropriately presented and easy to deliver, which are capable of stimulating effective B-cell, T-cell and cytotoxic immune responses whilst avoiding potentially hazardous and undesirable effects. Furthermore, the use of a mixture of defined epitopes could lead to an effective broad range immune response which has the potential to overcome both strain specificity of the pathogen and the MHC restriction of the host. Epitope-based vaccines can be designed to involve the use of synthetic materials that can be available in unlimited quantities and posing no biohazard. Other approaches include the use of naked DNA or recombinant viruses or bacteria expressing the epitopes. An important objective in the development of such vaccines is that they should be effective when delivered via the mucosal route and effective in the presence of maternal antibodies. In this review, we present examples of the use of various epitope-based vaccine constructs, focussing particularly upon their intranasal delivery to the immune system.

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.

An efficacious recombinant subunit vaccine against the salmonid rickettsial pathogen Piscirickettsia salmonis

Piscirickettsia salmonis is the aetiological agent of salmonid rickettsial septicaemia, an economically devastating rickettsial disease of farmed salmonids. Infected salmonids respond poorly to antibiotic treatment and no effective vaccine is available for the control of P. salmonis. Bacterin preparations of P. salmonis were found to elicit a dose-dependent response in coho salmon (Oncorhynchus kisutch), which varied from inadequate protection to exacerbation of the disease. However, an outer surface lipoprotein of P. salmonis, OspA, recombinantly produced in Escherichia coli elicited a high level of protection in vaccinated coho salmon with a relative percent survival as high as 59% for this single antigen. In an effort to further improve the efficacy of the OspA recombinant vaccine, T cell epitopes (TCE's) from tetanus toxin and measles virus fusion protein, that are universally immunogenic in mammalian immune systems, were incorporated tandemly into an OspA fusion protein. Addition of these TCE's dramatically enhanced the efficacy of the OspA vaccine, reflected by a three-fold increase in vaccine efficacy. These results represent a highly effective monovalent recombinant subunit vaccine for a rickettsia-like pathogen, P. salmonis, and for the first time demonstrate the immunostimulatory effect of mammalian TCE's in the salmonid immune model. These results may also be particularly pertinent to salmonid aquaculture in which the various subspecies are outbred and of heterologous haplotypes.

Immunocontrol in dogs

Population control in dogs and cats is an important goal for many groups. Control measures over the years has included surgery, hormonal therapy and more recently immunological control. The current presentation discusses dog population control with an emphasis on immunologic control. Specifically, vaccination with purified zona pellucida (ZP) glycoproteins leads initially to immunocontraception and then to the profound and irreversible changes of immunosterilization. The preliminary studies are extremely encouraging on developing a vaccine for lasting canine population control.

Protection against measles virus-induced encephalitis by anti-mimotope antibodies: the role of antibody affinity

Synthetic peptides mimicking a conformational B-cell epitope (M2) of the measles virus fusion protein (MVF) were used for the immunization of BALB/c mice and the anti-peptide and anti-virus antibody titers induced were compared. Of the panel of tested peptides, a chimeric peptide consisting of two copies of a T-helper epitope (residues 288-302 of MVF) and one copy of the mimotope M2 (TTM2) and a multiple antigen peptide with eight copies of M2 (MAP-M2) induced the highest titers of anti-M2 and anti-MV antibodies. Furthermore, peptides TTM2 and MAP-M2 induced antibodies with highest affinity for the mimotope and highest avidity for measles virus. Immunization with the MAP-M2 construct induced high titers of high-affinity anti-M2 antibody despite the absence of a T-helper epitope, and lymphocyte proliferation data suggest that the addition of M2 to the MAP resulted in the generation of a structure capable of stimulating T-cell help. Sera with anti-M2 reactivity were pooled according to affinity values for binding to M2, and high- and low-affinity pools were tested for their ability to prevent MV-induced encephalitis in a mouse model. The high-affinity serum pool conferred protection in 100% of mice, whereas the lower affinity pool conferred protection to only 50% of animals. These results indicate the potential of mimotopes for use as synthetic peptide immunogens and highlight the importance of designing vaccines to induce antibodies of high affinity.

Epitope mapping of the outer membrane protein P5-homologous fimbrin adhesin of nontypeable Haemophilus influenzae

To identify potential immunodominant and/or adhesin binding domains of the outer membrane protein P5-homologous fimbrin adhesin of nontypeable Haemophilus influenzae (NTHI), three sets of synthetic peptides were synthesized and assayed in an adherence inhibition assay, by Western blotting, and in a biomolecular interaction analysis (BIA) system. The first series of 34 8- to 10-mer peptides represented the entire mature protein sequentially. The second set of four peptides (each 19 to 28 residues) represented the four predicted major surface-exposed regions (or loops) of this adhesin. The third series of seven peptides (each 27 to 34 residues) were specifically designed to map the third surface-exposed region. Data obtained by BIA indicated limited reactivity of a panel of high-titered immune chinchilla sera to the 8- to 10-mer peptides representing the mature protein, likely because these linear peptides did not represent continuous epitopes. However, several of these short peptides did inhibit adherence of multiple NTHI strains to a human respiratory epithelial cell. Overall, greatest relative reactivity in both BIA and adherence inhibition assays was demonstrated against, or shown by, peptides mapping to the third and fourth predicted surface-exposed regions of this adhesin, thereby indicating the presence of immunodominant and adhesin binding domains at these sites. Middle ear fluids sequentially recovered from a chinchilla with an ongoing NTHI-induced otitis media (OM) as well as sera from children with OM due to NTHI also reacted exclusively with peptides representing the third and fourth surface-exposed regions of the P5-fimbrin adhesin, indicating a similarity in immune recognition of this bacterial protein by these two hosts. Collectively, these data together with the previously demonstrated protective efficacy of immunogens derived from this adhesin in chinchilla models support the continued development of P5-fimbrin based vaccine components.

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

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

Design of highly immunogenic liposomal constructs combining structurally independent B cell and T helper cell peptide epitopes

We have designed liposomal diepitope constructs that allow the physical combination, within the same vesicle, of B and Th epitopes as structurally separate entities. The immune response against such constructs was explored using TPEDPTDPTDPQDPSS (TPE), a B cell epitope originating from a Streptococcus mutans surface adhesin and QYIKANSKFIGITEL (QYI), a "universal" Th epitope from tetanus toxin. The two peptides were linked to the outer surface of small (diameter approximately 100 nm) unilamellar liposomes by covalent conjugation to two different anchors. To that end we have developed a strategy that allows the controlled chemical coupling of TPE and QYI, functionalized at their N terminus with a thiol, to preformed liposomes containing thiol-reactive derivatives of phosphatidylethanolamine and the lipopeptide S-[2,3-bis (palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-cysteinyl-alanyl-gly cine (Pam3CAG), respectively. This synthetic construct (administered i.p. to BALB/c mice) induced highly intense (titers > 20,000), anamnestic and long-lasting (over 2 years) immune responses, indicating that this strategy is successful. Two parameters were of prime importance to elicit this response with our liposomal diepitope constructs: (1) the simultaneous expression of B and Th epitopes on the same vesicle, and (2) the lipopeptide Pam3CAG anchor of the Th epitope QYI could not be replaced by a phosphatidylethanolamine anchor (a lesser immune response was observed). Analysis of the antibody response revealed a complex pattern; thus, besides the humoral response (production of IgG1, IgG2a, IgG2b) a superposition of a T-independent (TI-2 type) response was also found (IgM and IgG3). These results indicate that liposomal diepitope constructs could be attractive in the development of synthetic peptide-based vaccines.

Enhancement of the immunogenicity of a synthetic peptide bearing a VP3 epitope of hepatitis A virus

The immune responses elicited in mice by different forms of the VP3(110-121) B-epitope of the hepatitis A virus (HAV) were studied. Different forms of incorporation in liposomes were tested, encapsulation, rather than surface exposure, being the best antigenic preparation. Three larger peptides of the VP3 epitope, two of them containing a hepatitis B virus T-epitope, and a third containing a putative T-epitope of HAV (VP3(102-121)) were assayed. While this latter T-epitope induced an enhancement of the response against the VP3 B-epitope, the artificially coupled T-epitopes failed to induce a significant increase. The administration of two multiple antigenic peptide (MAP) constructs, the first containing the VP3(110-121) and VP1(11-25) HAV sequences and the second only the VP1(11-25) sequence, also suggested the presence of a T-epitope, since the response against the VP1 peptide was increased in the first construct.

Characterization of immune responses to experimental polyvalent subunit vaccines assembled in iscoms

Immune responses to experimental polyvalent subunit vaccines assembled in a particulate adjuvant/delivery system, iscoms, are described. The fusion protein ZZ-M5 comprises structures of staphylococcal protein A (ZZ) and the Plasmodium falciparum malaria antigen Pf155/RESA (M5). MHC congenic mice were immunized with ZZ-M5 conjugated to iscoms containing human influenza virus antigen (flu ag, M5-flu-isc) or to iscom matrix (iscom particles without flu ag, M5-isc). Comparison of antibody and T-cell responses to M5-isc and M5-flu-isc demonstrated that the flu ag in M5-flu-isc exhibits carrier-related helper functions and that the assembly of immunogens in M5-flu-isc did not result in any apparent antigenic competition. In addition, assembly of ZZ-M5 and flu ag in iscoms induced an alteration of the IgG subclass profile of the antibody response to M5. The results suggest that assembly of immunogens in iscoms may be a useful approach to the design of subunit vaccines but that both quantitative and qualitative aspects of the immunogenic properties of such constructs should be scrutinized.

Specificity of the T-cell responses in covalently linked peptides each comprising of a T helper epitope

The selection of T-cell specificities in chimeric peptides comprising of two T helper epitopes (288-302 and 240-252) from the fusion protein of measles virus was investigated. The resulting chimeric peptides (288-P-240 and 240-P-288) were shown to be immunogenic by inducing proliferative responses in both B10.s and C57BL/6 strains of mice. In B10.s mice immunization with the chimeric peptides resulted in proliferative T-cell responses only to the constituent 288-302 peptide, whereas in C57BL/6 mice no proliferative responses to the constituent 288-302 or 240-252 peptides were detected. In vivo competition studies between the 288-302 and 240-252 peptides for binding to the I-As molecule have shown that the peptide 288-302 was dominant in B10.s mice and competed with the non-dominant 240-252 peptide for the induction of an in vivo response. The absence of any proliferative T-cell response to the constituent 288-302 and 240-252 peptides after immunization of C57BL/6 mice with the 288-P-240 or 240-P-288 chimeric peptides, suggests that the dominant T-cell responses might have shifted to newly formed T cell epitope(s) as a result of the covalent linkage of the two peptides. In conclusion, these results indicate that the selection of Th epitopes within chimeric peptides is dependent not only on the amino acid composition of the epitope but also on the context of the epitope within the chimera and the haplotype of the mouse strain used.

The specificity of antibodies raised against a T cell peptide is influenced by peptide amidation

Peptides used for immunization are designed on the basis of combination of B and T cell epitopes. They are sometimes acetylated and amidated in order to mimic the protein insertion of the B cell epitope, but to our knowledge the effect of modifying the N- and C-termini is not clearly identified. In this paper, we have investigated in detail the influence of amidation and acetylation on the immunogenic properties of the T cell epitope 24-36 which is derived from a snake neurotoxin. Acetylation enhanced the capacity of the peptides to bind to I-Ed and to stimulate specific T cells in vitro but both modifications did not influence in vivo the T cell priming ability of the peptides. However, amidation of the peptides 24-36 provoked a dramatic effect on the antibody specificity they elicited, whereas acetylation did not. Antibodies recruited by amidated peptides weakly recognized the non amidated ones, while the latter elicited antibodies which hardly bind to the former. These results show how a subtle chemical change of a peptide immunogen modifies the reactivity of the elicited antibodies in an unrelated manner from the peptide MHC II binding ability and T cell stimulating capacity. We thus amplify the previously described polarity of chimeric TB peptides that raise antibodies mainly against their C-terminal part. Finally, these results may also facilitate the choice of the status of N and C termini of the peptides designed for immunization which at present have their extremities indifferently free or modified by acetylation and/or amidation.

Tandem repeats of T helper epitopes enhance immunogenicity of fusion proteins by promoting processing and presentation

Empirical findings have shown that recombinant chimeric proteins may be made more immunogenic if T helper epitopes are incorporated as tandem repeats. In the present study we investigated the mechanisms responsible for the enhanced immunogenicity of fusion proteins composed of the heat-stable enterotoxin of enterotoxigenic E. coli (STa) linked to multiple copies of the ovalbumin323-339 T helper epitope (ova) and a connecting dimer of an Ig-binding region of Staphylococcus aureus protein A (ZZ), which were previously shown to stimulate strong anti-STa titres in mice. We used B cell and macrophage cell lines as APC and IL-2 production by ova-specific T cells as our read-out system. Fusion proteins containing four repeated T helper epitopes were found to be the most immunogenic and resulted in 50-fold higher IL-2 production than constructs with a single T helper epitope. Under limiting APC conditions the construct with four epitopes was the best inducer of IL-2, indicating that this construct was most effectively processed by the APC. Analysis of IL-2R alpha expression by flow cytometry confirmed that four copies gave the highest frequency of activated T cells in culture, indicating a direct correlation between ability to activate T cells and IL-2 production in culture. Also in vivo, the fusion protein with four epitopes exhibited the strongest T cell priming effect. Moreover, both in vitro and in vivo, the ZZ construct was found to serve as an efficient means for targeting of the fusion proteins to B cells, thereby allowing access to the Ig receptor uptake pathway for Ag. The present study provides direct evidence that fusion proteins can be constructed to optimize processing in the individual APC and enhance activation of clonal T cells.

ZP3 peptide vaccine that induces antibody and reversible infertility without autoimmune oophoritis

Autoantibodies to ZP3, a major glycoprotein of the zona pellucida (ZP) with sperm receptor function, can block sperm/oocyte interaction. However, only mice of certain major histocompatibility complex (MHC) haplotype respond to the ZP3 peptide. Moreover, ZP3-specific T cells can mediate ovarian autoimmune disease. A chimeric peptide has been designed that induces antibody to native ZP3 regardless of the MHC haplotype of the inbred mice tested. This results in reduction in fertility that is reversible. Infertility correlates well with ZP antibody titer, and the mice do not develop concomitant autoimmune oophoritis. The vaccine contains (1) a promiscuous foreign T-cell peptide capable of eliciting a T-cell response regardless of the animals' MHC haplotype, and (2) a modified native B-cell peptide of ZP3.

The effect of orientation within a chimeric peptide on the immunogenicity of Chlamydia trachomatis epitopes

Peptides representing the Chlamydia trachomatis major outer membrane protein variable domains (VD) 1 and 4 of serovars C and E, respectively, have been shown to elicit a neutralizing antibody response in mice. To assess whether the position within a chimeric peptide influences the immunogenicity of the epitopes, two constructs, VD 1-4 and VD 4-1, were made in which the position of the VD relative to the amino and carboxy terminals were rotated. C57BL/10 mice were immunized with 100 micrograms of peptide in complete Freund's adjuvant (FA) on day 0, followed by an immunization with peptide (100 micrograms) in complete FA on day 14. By day 21 the immunodominant epitope in both chimeras as measured by ELISA was the one located at the carboxy terminus. A pepscan of the VD 1-4 antisera revealed a main peak in VD 4 which had been previously identified by neutralizing MAbs. The VD 4-1 antisera gave a peak in the VD 1 region which did not correspond to regions previously mapped with neutralizing MAbs. The VD 1-4 antisera but not the VD 4-1 antisera was able to neutralize in vitro serovar E. In summary, the position of these chlamydial epitopes within a chimeric peptide greatly influenced the resulting immune response.

Induction of measles virus-specific cytotoxic T-cell responses after intranasal immunization with synthetic peptides

We have investigated the structural requirements for the induction of cytotoxic T-cell responses (CTL) in vivo after intranasal immunization with an immunodominant CTL epitope from the nucleoprotein of measles virus (MV). For the induction of CTL responses, covalent linkage of the CTL epitope to a helper T-cell epitope was required and the orientation of the epitopes influenced the immunogenicity of the CTL epitope. The presence of two copies as compared with one copy of a T-helper epitope, rendered the CTL epitope more immunogenic and resulted in the in vivo induction of MV-specific CTLs without the need for an adjuvant. The role of CTL responses to this epitope in protection after intranasal administration was evaluated in a mouse model against challenge with a neuroadapted strain of MV. Although a decreased mortality in the peptide immunized compared with that in unimmunized mice was observed, the protection achieved was not significant. These findings highlight the importance of the rational design of synthetic immunogens for the induction of CTL responses and the potential of the intranasal route for immunization.

An antigenic peptide inducing cross-reacting antibodies inhibiting the interaction of Streptococcus mutans PAc with human salivary components

A 190-kDa surface protein antigen (PAc) of Streptococcus mutans, in particular the A region of this molecule, may be implicated in the induction of dental caries via an interaction with salivary components. For this reason, it was probably used successfully as an antigenic component for experimental vaccination to prevent dental caries in animals. While developing a synthetic peptide vaccine for dental caries, as reported herein, we have identified a unique peptide, TYEAALKQYEADL, as a candidate vaccinal immunogen. The amino acid sequence of this peptide completely corresponds to the sequence of a B-cell epitope in the A region of PAc and additionally contains its own T-cell epitope for B10.D2 mice within the molecule. This peptide strongly induces the production of only cross-reacting antibodies against PAc. In addition, as demonstrated by surface plasmon resonance analysis using the BIAcore system, these cross-reacting antibodies inhibit approximately 50% of the binding of fluid-phase salivary components to immobilized recombinant PAc.

Induction of systemic immune responses to measles virus synthetic peptides administered intranasally

A systemic antibody response was induced when a chimeric peptide containing two copies of a promiscuous T-cell epitope and one copy of a B-cell epitope (TTB) from the fusion protein of measles virus (MV) was administered to mice intranasally without adjuvant. A higher antibody titre was produced when the peptide was administered intranasally with cholera toxin B subunit (CTB) as an adjuvant and these antibodies crossreacted with the MV. Furthermore, splenocytes from intranasally immunized mice proliferated in vitro in the presence of the TTB peptide. The immune response following intranasal immunization with the peptide was influenced by the MHC haplotype of the strain of mice used. Thus CBA and BALB/c mice were high responders whereas C57BL/6 mice were low responders. Although peptide administered intranasally with CTB to CBA mice induced an immune response, no significant protection was observed against intra-cranial challenge with canine distemper virus which is antigenically related to MV.

Protection against morbillivirus-induced encephalitis by immunization with a rationally designed synthetic peptide vaccine containing B- and T-cell epitopes from the fusion protein of measles virus

Synthetic peptides representing T- and B-cell epitopes from the fusion (F) protein of measles virus (MV) were tested for their ability to induce a protective immune response against intracerebral challenge with neuroadapted strains of MV and canine distemper virus (CDV) in mice. Of the panel of peptides tested, only a chimeric peptide consisting of two copies of a promiscuous T-cell epitope (representing residues 288 to 302 of MV F protein) synthesized at the amino terminus of a B-cell epitope (representing residues 404 to 414 of MV F protein) was able to induce a protective response against challenge with MV and CDV in inbred mice. The protective response induced by this peptide (TTB) was associated with a significant reduction in mortality, histological absence of acute encephalitis, and greatly reduced titers of virus in the brains of TTB-immune mice following challenge compared with the results for nonimmunized controls. A chimeric peptide comprising one copy of the T-cell epitope and one copy of the B-cell epitope (TB) did not induce a protective response. A comparison of the antibody responses induced by the two chimeras suggested that differences in protective efficacy following immunization may be a result of the higher affinity of the antibody induced by the TTB peptide than that of the antibody induced by the TB peptide. In addition, differences in the immunoglobulin G subclass of the antipeptide antibody responses were observed, and these may play a role in the differences in protection observed. These results indicate that appropriately designed synthetic peptides have potential as vaccines for the induction of cross-reactive protection against morbilliviruses.

The affinity of IgG antibodies to gag p24 and p17 in HIV-1-infected patients correlates with disease progression

The affinity of anti-gag antibody was studied for up to 9 years (1984-1993) in sera from 15 HIV-1+ patients with haemophilia. On the basis of their 1993 clinical status patients were divided into two groups: (i) patients who remained asymptomatic (n = 9); and (ii) those who progressed to AIDS between late 1987 and 1993. The affinity constants of antibody for p24 and p17 were determined by a double isotope fluid-phase radioimmunoassay; and the relationships between antibody affinity and titre, patient clinical course, CD4 cell counts and p24 antigenaemia were analysed. The affinity of p24- and p17-specific antibody was up to 100 times greater in asymptomatic patients than in patients who progressed to AIDS. Patients who developed AIDS either lost or failed to develop high-affinity antibodies early in the infection. Asymptomatic patients maintained high-affinity antibodies for several years; however, in some of these patients the affinity of anti-p24 and p17 antibodies subsequently fell later in the study period. The presence of low-affinity antibody and progressive reduction in the titre of specific antibody were earlier predictors of disease onset than CD4 cell counts. The failure to either develop or maintain high affinity gag-specific antibody suggests an early impairment of T helper function in individuals who progressed to AIDS. The presence of antibody of high affinity could be essential in controlling virus replication and the onset of AIDS.

Dituftsin and polytuftsin induce an anti-peptide IgG response to non-immunogenic peptides in mice

The effect of covalently attaching multiple forms of the immunomodulating tetrapeptide tuftsin to normally non-immunogenic peptides was studied in BALB/c and C57Bl/6 mice. The peptides: (NANP)3 from the Plasmodium falciparum circumsporozoite protein and peptides 136-152 and 205-213 derived from the capsid protein of foot-and-mouth disease virus were coupled to polytuftsin or dituftsin. Anti-peptide IgG titers were determined after two immunizations. All of these three non-immunogenic peptides coupled to polytuftsin or dituftsin induced anti-peptide antibody production in mice while peptides alone did not elicit IgG. In addition, a conjugate of (NANP)3 and polytuftsin with built-in glycopeptide adjuvant elicited an anti-peptide response comparable in magnitude with that of a peptide-KLH conjugate. The data suggest that when non-immunogenic peptides are synthesized in tandem with dituftsin or conjugated to polytuftsin a significant immune response to the peptides may be elicited. This approach may be employed in synthetic vaccine design.

Fusion proteins with heterologous T helper epitopes. Recombinant E. coli heat-stable enterotoxin proteins

Fusion proteins containing specific B cell and T cell epitopes were used to examine how the intramolecular arrangement of T and B cell epitopes within a chimeric protein influences antigen-specific B cell antibody responses as well as specific T cell activation. Chimeric proteins, containing single or multiple copies of the Th epitope ovalbumin 323-339 (ova) linked at different positions to STa, the heat-stable enterotoxin of E. coli, were compared with respect to their ability to induce STa-specific antibody production and to induce ova-specific T cell activation. Chimeric proteins induced ova-dependent antibody production against STa at the amino terminal end, irrespective of the positioning of ova. Multiple tandem copies of ova in any position led to increased levels of antibody production against this epitope. In contrast, T cell help for antibody production against a second B cell epitope at the carboxy terminus of the fusion proteins was more effective after insertion of multiple copies of ova in a distal than in an adjacent position. A fusion protein, containing four copies of ova effectively elicited T cell help for antibody production against both examined B cell determinants, showing that activated Th cells recognizing a single epitope could simultaneously provide help for distinct sets of B cells specific for widely separated epitopes within a protein. T cell recognition of ova in all chimeric peptides, independently of its position, following the same pattern of genetic restriction (i.e. immunodominant in H-2d and nonimmunogenic in H-2k) as in the native ovalbumin molecule.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of epitope polarity and adjuvants on the immunogenicity and efficacy of a synthetic peptide vaccine against Semliki Forest virus

The antibody response to a previously defined B-cell epitope of Semliki Forest virus (SFV) was investigated in male BALB/c (H-2d) mice. The B-cell epitope, located at amino acid positions 240 to 255 of the E2 protein, was linked to an H-2d-restricted T-helper cell epitope of SFV located at positions 137 to 151 of the E2 protein. Colinearly synthesized peptides, of either T-B or B-T polarity, mixed with different adjuvants (the nonionic block copolymer L 180.5, a water-oil-water [W/O/W] emulsion of L 180.5, Montanide, and Q VAC) were used for immunization. Generally, after one booster immunization, high serum antibody titers were measured against either peptide. With Q VAC and W/O/W L 180.5 as adjuvants, the titers of SFV-reactive (nonneutralizing) antibodies were consistently much higher after immunization with the T-B peptide than with the B-T peptide, which was reflected in a higher vaccine efficacy. With these two adjuvants, the survival ratio in T-B peptide-immunized mice was 82%, compared with 8% in B-T peptide-immunized mice. Intermediate results were obtained with the adjuvant Montanide. L 180.5 alone was ineffective in this study. All immunoglobulin G (IgG) isotypes were induced with either adjuvant, but Q VAC was clearly the most effective in inducing IgG2a and IgG2b isotypes with the T-B peptide as the antigen. Subsequently, monoclonal antibodies (MAbs) of IgM, IgG1, IgG2a, IgG2b, and IgG3 subclasses were prepared against the B-cell epitope. These nonneutralizing but SFV-reactive MAbs protected 40 to 80% of mice against a lethal challenge with SFV. Control mice all died. The availability of those antipeptide MAbs allowed competition binding assays with a previously characterized panel of E2-specific MAbs. Binding of enzyme-labeled antipeptide MAbs was very effectively inhibited by two strongly SFV-neutralizing mutually competitive MAbs, suggesting that the linear B-cell epitope (amino acids 240 to 255) is associated with a major neutralization site of SFV.

Influence of the T-helper epitope on the titre and affinity of antibodies to B-cell epitopes after co-immunization

We have assessed the influence of different T-helper cell epitopes on the level and affinity of antibody to B-cell epitopes induced following co-immunization with free peptides mimicking epitopes from measles and respiratory syncytial virus envelope proteins. The responses obtained following co-immunization have been compared to those obtained following immunization with chimeric synthetic peptide immunogens in which the epitopes were covalently coupled. The results show that covalent linkage of the B- and T-cell epitopes is not necessary for the generation of T-cell dependent antibody responses to non-immunogenic B-cell epitopes. In addition the induction of memory B-cells required adjuvant but subsequent stimulation of these memory cells did not. The responses obtained were non-MHC restricted since co-immunization resulted in the production of antibody responses to B-cell epitopes in a panel of five inbred mouse strains but there were differences in the ability of different T-cell epitopes to provide help for antibody production to the same B-cell epitope. The affinity of antibodies to the B-cell epitopes induced following immunization with chimeric T:B peptides was higher than that obtained following co-immunization. These results indicate the value of co-immunization for the induction of antibody responses to B-cell epitopes across MHC differences and suggest that this strategy may be of value in the development of synthetic peptide vaccines. However, modifications of the approach need to be developed to ensure the production of antibody of the highest possible affinity.