Abdullah A. H. Ahmad Fuaad

Recent progress in adjuvant discovery for peptide-based subunit vaccines

Peptide-based subunit vaccines are of great interest in modern immunotherapy as they are safe, easy to produce and well defined. However, peptide antigens produce a relatively weak immune response, and thus require the use of immunostimulants (adjuvants) for optimal efficacy. Developing a safe and effective adjuvant remains a challenge for peptide-based vaccine design. Recent advances in immunology have allowed researchers to have a better understanding of the immunological implication of related diseases, which facilitates more rational design of adjuvant systems. Understanding the molecular structure of the adjuvants allows the establishment of their structure-activity relationships which is useful for the development of next-generation adjuvants. This review summarizes the current state of adjuvants development in the field of synthetic peptide-based vaccines. The structural, chemical and biological properties of adjuvants associated with their immunomodulatory effects are discussed.

Peptide Conjugation via CuAAC ‘Click’ Chemistry

The copper (I)-catalyzed alkyne azide 1,3-dipolar cycloaddition (CuAAC) or ‘click’ reaction, is a highly versatile reaction that can be performed under a variety of reaction conditions including various solvents, a wide pH and temperature range, and using different copper sources, with or without additional ligands or reducing agents. This reaction is highly selective and can be performed in the presence of other functional moieties. The flexibility and selectivity has resulted in growing interest in the application of CuAAC in various fields. In this review, we briefly describe the importance of the structural folding of peptides and proteins and how the 1,4-disubstituted triazole product of the CuAAC reaction is a suitable isoster for an amide bond. However the major focus of the review is the application of this reaction to produce peptide conjugates for tagging and targeting purpose, linkers for multifunctional biomacromolecules, and reporter ions for peptide and protein analysis.

Self-adjuvanting vaccine against group A streptococcus: Application of fibrillized peptide and immunostimulatory lipid as adjuvant

Peptides are of great interest to be used as vaccine antigens due to their safety, ease of manufacturing and specificity in generating immune response. There have been massive discoveries of peptide antigens over the past decade. However, peptides alone are poorly immunogenic, which demand co-administration with strong adjuvant to enhance their immunogenicity. Recently, fibril-forming peptides such as Q11 and lipoamino acid-based carrier have been identified to induce substantial immune responses when covalently linked to peptide epitope. In this study, we have incorporated either Q11 or lipoamino acids to a peptide epitope (J14) derived from M protein of group A streptococcus to develop self-adjuvanting vaccines. J14, Q11 and lipoamino acids were also conjugated together in a single vaccine construct in an attempt to evaluate the synergy effect of combining multiple adjuvants. Physicochemical characterization demonstrated that the vaccine constructs folded differently and self-assembled into nanoparticles. Significantly, only vaccine constructs containing double copies of lipoamino acids (regardless in conjugation with Q11 or not) were capable to induce significant dendritic cells uptake and subsequent J14-specific antibody responses in non-sizes dependent manners. Q11 had minimal impact in enhancing the immunogenicity of J14 even when it was used in combination with lipoamino acids. These findings highlight the impact of lipoamino acids moiety as a promising immunostimulant carrier and its number of attachment to peptide epitope was found to have a profound effect on the vaccine immunogenicity.

The use of a conformational cathepsin D-derived epitope for vaccine development against Schistosoma mansoni

Schistosomiasis is caused by the infection from Schistosoma species. Among these, Schistosoma mansoni is one of the major species that infects millions of people worldwide. The use of praziquantel is effective in clearing the infestation but treatment of a large and widespread population in endemic areas is unsustainable. Thus, synergistic approach of using drug and vaccination can serve as an alternative to the current treatment. In this study, we have developed vaccine candidates that composed of three components: a B-cell epitope derived from S. mansoni cathepsin D protein (Sm-CatD) flanked by GCN4 helix promoting peptide; a promiscuous T-helper epitope (P25); and a lipid core peptide system, in attempt to develop self-adjuvanting vaccine candidates against the schistosome. Physicochemical properties of the vaccine candidates were analysed and antibodies to each construct were raised in BALB/c mice. The vaccine candidates were able to self-assemble into particles that induced high titres of IgG without the use of additional adjuvant. The antibody levels were comparable to that induced by peptide formulated with strong but toxic Freunds adjuvant. The integration of a GCN4 sequence induced the helical conformation of the epitope, while the addition of the T helper peptide was very effective in inducing consistent IgG-specific antibodies response amongst mice. These findings are particularly encouraging for the development of efficient and immunogenic vaccine against schistosomiasis.

Lipopeptide Nanoparticles: Development of Vaccines against Hookworm Parasite.

Necator americanus (hookworm) infects over half a billion people worldwide. Anthelminthic drugs are commonly used to treat the infection; however, vaccination is a more favorable strategy to combat this parasite. We designed new B‐cell peptide epitopes based on the aspartic protease of N. americanus (Na‐APR‐1). The peptides were conjugated to self‐adjuvanting lipid core peptide (LCP) systems via stepwise solid‐phase peptide synthesis (SPPS) and copper catalyst azide–alkyne cycloaddition (CuAAC) reactions. The LCP vaccine candidates were able to self‐assemble into nanoparticles, were administered to mice without the use of additional adjuvant, and generated antibodies that recognized the parent epitope. However, only one LCP derivative was able to produce a high titer of antibodies specific to Na‐APR‐1; circular dichroism analyses of this compound showed a β‐sheet conformation for the incorporated epitope. This study provides important insight in epitope and delivery system design for the development of a vaccine against hookworm infections.

Group A Streptococcal Vaccine Candidates based on the Conserved Conformational Epitope from M Protein

Copper catalysed azide alkyne Huisgen cycloaddition (click) reaction assisted conjugation of the multiple copy of conserve epitope (J14) derived from Group A Streptococcal M-protein to LCP core induced desired α-helical conformation of the epitope. The constructs were able to self assemble into large nanoparticles under aqueous conditions. Immunological assessment of these particles demonstrated their capacity to elicit high-titer systemic IgG antibodies against the epitope without help of adjuvant. The LCP systems incorporating the epitope via its N- or C-termini did not elicit significantly different immune responses.

Synthesis and Characterisation of Self‐Assembled and Self‐Adjuvanting Asymmetric Multi‐Epitope Lipopeptides of Ovalbumin

Designing a lipopeptide (LP) vaccine with a specific asymmetric arrangement of epitopes may result in an improved display of antigens, increasing host-cell recognition and immunogenicity. This study aimed to synthesise and characterise the physicochemical properties of a library of asymmetric LP-based vaccine candidates that contained multiple CD4(+) and CD8(+) T-cell epitopes from the model protein antigen, ovalbumin. These fully synthetic vaccine candidates were prepared by microwave-assisted solid phase peptide synthesis. The C12 or C16 lipoamino acids were coupled to the N or C terminus of the OVA CD4 peptide epitope. The OVA CD4 LPs and OVA CD8 peptide constructs were then conjugated using azide-alkyne Huisgen cycloaddition to give multivalent synthetic vaccines. Physiochemical characterisation of these vaccines showed a tendency to self-assemble in aqueous media. Changes in lipid length and position induced self-assembly with significant changes to their morphology and secondary structure as shown by transmission electron microscopy and circular dichroism.

Development of Novel Melanocortin Receptor Agonists Based on the Cyclic Peptide Framework of Sunflower Trypsin Inhibitor-1

Ultrastable cyclic peptide frameworks offer great potential for drug design due to their improved bioavailability compared to their linear analogues. Using the sunflower trypsin inhibitor-1 (SFTI-1) peptide scaffold in combination with systematic N-methylation of the grafted pharmacophore led to the identification of novel subtype selective melanocortin receptor (MCR) agonists. Multiple bicyclic peptides were synthesized and tested toward their activity at MC1R and MC3-5R. Double N-methylated compound 18 showed a p Ki of 8.73 ± 0.08 ( Ki = 1.92 ± 0.34 nM) and a pEC50 of 9.13 ± 0.04 (EC50 = 0.75 ± 0.08 nM) at the human MC1R and was over 100 times more selective for MC1R. Nuclear magnetic resonance structural analysis of 18 emphasized the role of peptide bond N-methylation in shaping the conformation of the grafted pharmacophore. More broadly, this study highlights the potential of cyclic peptide scaffolds for epitope grafting in combination with N-methylation to introduce receptor subtype selectivity in the context of peptide-based drug discovery.

Nanoparticles-based peptide subunit vaccines against group A Streptococcus

No abstract is available for this article.