Design of peptide and polypeptide vaccines

Identification of by-products from an orthogonal peptide ligation by oxime bonds using mass spectrometry and tandem mass spectrometry

Synthetic proteins with unusual architecture are obtained through chemoselective ligation, a method based on the condensation of unprotected peptides under mild aqueous conditions. The last step of a new procedure leading to a tri-branched conjugate consists of the chemoselective ligation reaction between an (aminooxy)acetyl peptide and a peptide aldehyde resulting from a first ligation via an oxime bond. In order to optimize the reaction conditions, electrospray ionization mass spectrometry combined with liquid chromatography and tandem mass spectrometry has been used. In addition to the target tri-branched conjugate, two other conjugates were characterized allowing documentation of transoximation reactions in peptide chemistry. A fourth conjugate was identified as a side product appearing after the first ligation. Data obtained by low-energy collision-induced dissociation led to a rapid and reliable identification of impurities observed in the (aminooxy)acetyl peptide despite a previous high performance liquid chromatography (HPLC) purification. This highlights the great reactivity of the aminooxy group towards carbonyl-containing compounds.

Structural features of a chimeric peptide inducing cytotoxic T lymphocyte responses in saline

Little information is available correlating the structural properties of peptides with their immunogenicity in terms of responses via cytotoxic T lymphocytes (CTLs). The TT-NP6 chimeric peptide, consisting of two copies of a promiscuous T-helper epitope (T: residues 288-302 from the fusion protein of the measles virus) linked to the NP6 T-cytotoxic epitope (NP6: residues 52-60 from the nucleoprotein of measles virus) was able to induce virus-specific CTL responses in the absence of any adjuvant and hydrophobic component. The present work was undertaken to gain insight into structural features of the TT-NP6 peptide that may be important in optimizing the CTL immunogenicity of the peptide. Circular dichroism data, obtained in a buffer of physiological ionic strength and pH, strongly suggest a self-associated state for the peptide, which was confirmed by a sedimentation velocity experiment. However, helix association is accompanied by loss of overall helical content. Thermal-dependence studies show that the unfolding of self-associated alpha-helices is significantly more pronounced than the unfolding of isolated alpha-helices. Circular dichroism data, together with tryptic limited proteolysis, suggest the presence of a charged amino acid within the hydrophobic core. This study should provide a basis for engineering more effective immunogenic peptides against the measles virus by increasing the stability of the TT-NP6 peptide.

Intranasal administration of synthetic recombinant peptide-based vaccine protects mice from infection by Schistosoma mansoni

Schistosomiasis is the cause of a chronic debilitating disease which accounts for significant mortality and morbidity every year, especially in tropical and subtropical areas. An epitope derived from the protective surface protein 9B-Ag of Schistosoma mansoni, designated 9B peptide-1, was previously showed to be protective in mice when conjugated to bovine serum albumin and administered subcutaneously in complete Freund's adjuvant. In this work, this protective peptide was expressed in the flagellin of a Salmonella vaccine strain, and the isolated recombinant flagella were used for immunization of mice. Since during the invasion of the parasite into the host the schistosomula migrate first to the lungs, the intranasal route of administration was employed in order to halt the parasite at an early stage of the infection. Such intranasal immunization with this peptide expressed in flagellin, without the addition of adjuvants, resulted in a significant humoral response and also led to protection against challenge infection, manifested as a reduction of the worm burden by an average of 42%.

Production of recombinant subunit vaccines: protein immunogens, live delivery systems and nucleic acid vaccines

The first scientific attempts to control an infectious disease can be attributed to Edward Jenner, who, in 1796 inoculated an 8-year-old boy with cowpox (vaccinia), giving the boy protection against subsequent challenge with virulent smallpox. Thanks to the successful development of vaccines, many major diseases, such as diphtheria, poliomyelitis and measles, are nowadays kept under control, and in the case of smallpox, the dream of eradication has been fulfilled. Yet, there is a growing need for improvements of existing vaccines in terms of increased efficacy and improved safety, besides the development of completely new vaccines. Better technological possibilities, combined with increased knowledge in related fields, such as immunology and molecular biology, allow for new vaccination strategies. Besides the classical whole-cell vaccines, consisting of killed or attenuated pathogens, new vaccines based on the subunit principle, have been developed, e.g. the Hepatitis B surface protein vaccine and the Haemophilus influenzae type b vaccine. Recombinant techniques are now dominating in the strive for an ideal vaccine, being safe and cheap, heat-stable and easy to administer, preferably single-dose, and capable of inducing broad immune response with life-long memory both in adults and in infants. This review will describe different recombinant approaches used in the development of novel subunit vaccines, including design and production of protein immunogens, the development of live delivery systems and the state-of-the-art for nucleic acids vaccines.

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.

A mutational approach shows similar mechanisms of recognition for the isolated and integrated versions of a protein epitope

Antibody mAb164 is directed against the native form of the TrpB2 subunit of Escherichia coli tryptophan synthase. It recognizes a synthetic peptide, P11, constituted of residues 273-283 of TrpB, with high affinity. We introduced 16 single and 3 double mutations in each of the two contexts, TrpB2 and P11, and used them as local probes to study the cross-reactivity of mAb164 toward these two antigens. The equilibrium constant, KD, of dissociation from mAb164 was measured for each of the mutant derivatives of TrpB2 and P11 by a competition enzyme-linked immunosorbent assay and compared with the wild type one. The variation of the free energy of interaction, DeltaDeltaG, covered nearly 8 kcal/mol for the different mutations. The values of DeltaDeltaG for the mutant derivatives of TrpB2 and for those of P11 were close and the two sets of values were strongly correlated (r = 0.96). This correlation showed that mAb164 recognized the integrated and isolated versions of residues 273-283 with very similar mechanisms. A few significant differences between the recognitions of TrpB2 and P11 by mAb164 suggested some adaptability of the interaction. The results were compatible with a recognition of residues 273-283 of TrpB in a loop conformation, close to their structure in the crystals of the complete tryptophan synthase, TrpA2TrpB2.

Synthesis and characterization of a protective peptide-based vaccine against Schistosoma mansoni

Two synthetic peptides, corresponding to the N-terminal sequence of the 45-kDa subunit of the protective 9B antigen of Schistosoma mansoni and differing in only one amino acid residue, were synthesized. These peptides were recognized by the protective monoclonal antibody 152-66-9B, as well as by sera of mice and humans infected with schistosomiasis. The peptides were coupled to a protein carrier and used for immunization. One of the peptides, 9B-peptide1, induced in mice significant protection against challenge infection, manifested in a 40 to 50% reduction in worm burden.

Epitope-specific focusing of the immune response to a minimized human chorionic gonadotropin analog

Minimized proteins have long been used to elicit an immune response to particular regions of a protein antigen. Most efforts to derive minimized proteins have employed synthetic peptide fragments. This approach works well for linear epitopes but poorly for conformational epitopes. Here we describe a homodimeric human chorionic gonadotropin (hCG) analog that retains the conformation of related parts of hCG and elicits high affinity specific antibodies. This novel immunogen displays the tertiary structure of selected loops of the protein but lacks structures that could elicit potentially undesirable antibodies.