Strategies and Limitations in Dendrimeric Immunogen Synthesis. The Influenza Virus M2e Epitope as a Case Study

Peptide-Based Vaccines: Foot-and-Mouth Disease Virus, a Paradigm in Animal Health

Vaccines are considered one of the greatest global health achievements, improving the welfare of society by saving lives and substantially reducing the burden of infectious diseases. However, few vaccines are fully effective, for reasons ranging from intrinsic limitations to more contingent shortcomings related, e.g., to cold chain transport, handling and storage. In this context, subunit vaccines where the essential antigenic traits (but not the entire pathogen) are presented in rationally designed fashion have emerged as an attractive alternative to conventional ones. In particular, this includes the option of fully synthetic peptide vaccines able to mimic well-defined B- and T-cell epitopes from the infectious agent and to induce protection against it. Although, in general, linear peptides have been associated to low immunogenicity and partial protection, there are several strategies to address such issues. In this review, we report the progress towards the development of peptide-based vaccines against foot-and-mouth disease (FMD) a highly transmissible, economically devastating animal disease. Starting from preliminary experiments using single linear B-cell epitopes, recent research has led to more complex and successful second-generation vaccines featuring peptide dendrimers containing multiple copies of B- and T-cell epitopes against FMD virus or classical swine fever virus (CSFV). The usefulness of this strategy to prevent other animal and human diseases is discussed.

Trimeric heptad repeat synthetic peptides HR1 and HR2 efficiently inhibit HIV-1 entry

The trimeric heptad repeat domains HR1 and HR2 of the human immunodeficiency virus 1 (HIV-1) gp41 play a key role in HIV-1-entry by membrane fusion. To develop efficient inhibitors against this step, the corresponding trimeric-N36 and C34 peptides were designed and synthesized. Analysis by circular dichroism of monomeric and trimeric N36 and C34 peptides showed their capacities to adopt α-helical structures and to establish physical interactions. At the virological level, while trimeric-C34 conserves the same high anti-fusion activity as monomeric-C34, trimerization of N36-peptide induced a significant increase, reaching 500-times higher in anti-fusion activity, against R5-tropic virus-mediated fusion. This result was associated with increased stability of the N36 trimer peptide with respect to the monomeric form, as demonstrated by the comparative kinetics of their antiviral activities during 6-day incubation in a physiological medium. Collectively, our findings demonstrate that while the trimerization of C34 peptide had no beneficial effect on its stability and antiviral activity, the trimerization of N36 peptide strengthened both stability and antiviral activity. This approach, promotes trimers as new promising HIV-1 inhibitors and point to future development aimed toward innovative peptide fusion inhibitors, microbicides or as immunogens.

Peptide dendrimers as valuable biomaterials in medical sciences

Peptides are oligomers of amino acids, which have been used in a wide range of applications, particularly in medical and pharmaceutical sciences. Linear peptides have been extensively developed in various fields of medicine as therapeutics or targeting agents. The branched structure of peptide dendrimers with peptide (commonly, poly l‑Lysine) or non-peptide (commonly poly‑amidoamine) core, often exhibits valuable novel features, improves stability and enhances the functionality of peptide in comparison with small linear peptides. The potential applications of Branched and hyper-branched peptidic structures which are known as peptide dendrimers in biomedical sciences have been approved vastly. A peptide dendrimer contains three distinct parts including core, building blocks and branching units or surface functional groups. These structures provide a lot of opportunities in the pharmaceutical field, particularly for novel drug development. In this review, a brief summary of different biomedical applications of peptide dendrimers is presented, and peptide dendrimers as active pharmaceutical ingredients and drug delivery carriers are discussed. Applications of peptide dendrimers in vaccines and diagnostic tools are also presented, in brief. Generally, peptide dendrimers are promising biomaterials with high evolution rate for clinical and non-clinical applications in medicine.

Branched BBB-shuttle peptides: chemoselective modification of proteins to enhance blood-brain barrier transport

The blood-brain barrier (BBB) hampers the delivery of therapeutic proteins into the brain. BBB-shuttle peptides have been conjugated to therapeutic payloads to increase the permeability of these molecules. However, most BBB-shuttles have several limitations, such as a lack of resistance to proteases and low effectiveness in transporting large biomolecules. We have previously reported on the THRre peptide as a protease-resistant BBB-shuttle that is able to increase the transport of fluorophores and quantum dots in vivo. In this work, we have evaluated the capacity of linear and branched THRre to increase the permeability of proteins in cellular models of the BBB. With this purpose, we have covalently attached peptides with one or two copies of the BBB-shuttle to proteins in order to develop chemically well-defined peptide-protein conjugates. While THRre does not enhance the uptake and transport of a model protein in BBB cellular models, branched THRre peptides displaying two copies of the BBB-shuttle result in a 2.6-fold increase.

A lipidated form of the extracellular domain of influenza M2 protein as a self-adjuvanting vaccine candidate

The highly conserved extracellular domain of Matrix protein 2 (M2e) of influenza A virus has been previously investigated as a potential target for an universal influenza vaccine. In this study we prepared four lipopeptide influenza vaccine candidates in which the TLR2 agonist S-[2,3-bis(palmitoyloxy)propyl] cysteine, (Pam2Cys) was attached to either the N- or C-terminus of the M2e consensus sequence SLLTEVETPIRNEWGCRCNDSSDP and its analogue sequence with the two cysteine residues replaced with serine residues. The results of animal study show that each of these lipopeptides induced strong M2e-specific antibody responses in the absence of extraneous T helper cell epitope(s) which are normally incorporated in the previous studies or addition of extraneous adjuvant and that these antibodies are protective against lethal challenge with influenza virus. Comparison of different routes of inoculation demonstrated that intranasal administration of M2e lipopeptide induced higher titers of IgA and IgG2b antibodies in the bronchoalveolar lavage than did subcutaneous vaccination and was better at mitigating the severity of viral challenge. Finally, we show that anti-M2e antibody specificities absent from the antibody repertoire elicited by a commercially available influenza vaccine and by virus infection can be introduced by immunization with M2e-lipopeptide and boosted by viral challenge. Immunization with this lipidated form of the M2e epitope therefore offers a means of using a widely conserved epitope to generate protective antibodies which are not otherwise induced.

Taming the TCR: antigen-specific immunotherapeutic agents for autoimmune diseases

Current treatments for autoimmune diseases are typically non-specific anti-inflammatory agents that affect not only the autoreactive cells but also the parts of the immune system that are required to maintain health. There is a need for the development of antigen-specific therapeutic agents that can effectively prevent the autoimmune attack while leaving the rest of the immune system functioning as normal. The simplest way to achieve this is using the autoantigen itself as a tolerizing agent; however, there is some risk involved with administering a potentially pathogenic antigen. In this review, we focus instead on the development and use of modified T cell receptor (TCR) ligands, in which the peptide ligand is modified to change the response by the T cell from a disease inducing to a protective response, and still retain the antigen-specificity necessary to target the autoreactive T cells. We review the use of modified TCR ligands as therapeutic agents in animal models of autoimmunity and in human autoimmune disease, and finally consider how they need to be improved in order to use them effectively in patients with autoimmune disease.

Glycodendropeptides stimulate dendritic cell maturation and T cell proliferation: a potential influenza A virus immunotherapy

A GDP displaying the NP_366–374 influenza A virus epitope induces an immunostimulatory effect, emerging as a potential flu vaccine.

Gold nanoparticle-M2e conjugate coformulated with CpG induces protective immunity against influenza A virus

AIM

This study aimed to develop a novel influenza A vaccine by conjugating the highly conserved extracellular region of the matrix 2 protein (M2e) of influenza A virus to gold nanoparticles (AuNPs) and to test the vaccine in a mouse influenza challenge model.

MATERIALS & METHODS

Citrate-reduced AuNPs (diameter: 12 nm) were synthesized, and characterized by transmission electron microscopy and dynamic light scattering. M2e was conjugated to AuNPs through thiol-gold interactions to form M2e-AuNP conjugates. Particle stability was confirmed by UV-visible spectra, and M2e conjugation was further characterized by x-ray photoelectron spectroscopy. Mice were immunized with M2e-AuNPs with or without CpG (cytosine-guanine rich oligonucleotide) as an adjuvant with appropriate control groups. Sera was collected and M2e-specific immunoglobulin (IgG) was measured, and immunized mice were challenged with PR8-H1N1 influenza virus.

RESULTS

M2e-capped AuNPs could be lyophilized and stably resuspended in water. Intranasal vaccination of mice with M2e-AuNP conjugates induced M2e-specific IgG serum antibodies, which significantly increased upon addition of soluble CpG as adjuvant. Upon challenge with lethal PR8, mice vaccinated with M2e-AuNP conjugates were only partially protected, while mice that received soluble CpG as adjuvant in addition to M2e-AuNP were fully protected.

CONCLUSION

Overall, this study demonstrates the potential of using the M2e-AuNP conjugates with CpG as an adjuvant as a platform for developing an influenza A vaccine.

Influence of conjugation chemistry and B epitope orientation on the immune response of branched peptide antigens

Multimeric presentation, a well-proven way of enhancing peptide immunogenicity, has found substantial application in synthetic vaccine design. We have reported that a combination of four copies of a B-cell epitope with one of a T-cell epitope in a single branched construct results in a peptide vaccine conferring total protection against foot-and-mouth disease virus in swine, a natural host (Cubillos et al. (2008) J. Virol. 82, 7223-7230). More recently, a downsized version of this prototype with only two copies of the B epitope has proven as effective as the tetravalent one in mice. Here we evaluate three approaches to bivalent platforms of this latter type, involving different chemistries for the conjugation of two B epitope peptides to a branching T epitope. Comparison of classical thioether, "reverse" thioether (Monsó et al. (2012) Org. Biomol. Chem. 10, 3116-3121) and thiol-ene conjugation chemistries in terms of synthetic efficiency clearly singles out the latter, maleimide-based strategy as most advantageous. We also examine how minor structural differences among the conjugates--including the N- or C-terminal attachment of the B epitope to the branching T epitope--bear on the immunogenicity of these vaccine candidates, with the maleimide-based conjugate again emerging as the most successful.

Reverse thioether ligation route to multimeric peptide antigens

Multimeric presentation, a rather effective way of enhancing peptide immunogenicity, is best exemplified by MAP (multiple antigenic peptide) dendrimers consisting of a branched Lys core on which several copies of the peptide epitope are displayed. While accessible by solid-phase synthesis, MAPs can also be conveniently made in solution, e.g., by linking the epitope (N-acetylated and with a C-terminal Cys) through a thioether bond onto the α and ε (haloacetyl-activated) positions of the Lys core. We now report the reverse version of this approach, whereby a chloroacetyl-derivatised epitope is tethered to a thiol-functionalised form of a Lys dendron core. This convergent approach can be carried out either in solution or in the solid phase and is advantageous because (i) in situ tris(2-carboxyethyl)phosphine (TCEP)-mediated reduction of disulfide bonds maintains the thiol platform reactive throughout the ligation process; (ii) the low amounts of TCEP used pose minimal risk to chloroacetyl groups in the peptide, resulting in (iii) significantly reduced byproduct formation, hence cleaner products. For the solid phase version of the method, an optimised procedure has been devised to convert the Lys core into a tetrathiol dendron.

ChemMatrix(®) for complex peptides and combinatorial chemistry

CM resin is a totally PEG-based resin, made exclusively from primary ether bonds and therefore highly chemically stable. Compared to other PEG resins, it exhibits good loading and is user friendly because of its free-flowing form upon drying. It shows improved performance over PS resins for the preparation of hydrophobic, highly structured poly-Arg peptides. In combination with ψPros, it allows the synthesis of small proteins such as the chemokine RANTES. Like other PEG-based resins, CM resin swells well in biocompatible solvents such as water, thereby allowing on-bead screening. Furthermore, the high loading of this resin permits the use of a tiny quarter of a bead as a microreactor for HPLC and MALDI-TOF analysis, thus further extending its applications in the field of combinatorial chemistry.