A nonadjuvanted polypeptide nanoparticle vaccine confers long-lasting protection against rodent malaria

Harnessing self-assembled peptide nanoparticles in epitope vaccine design

Vaccination has been one of the most successful breakthroughs in medical history. In recent years, epitope-based subunit vaccines have been introduced as a safer alternative to traditional vaccines. However, they suffer from limited immunogenicity. Nanotechnology has shown value in solving this issue. Different kinds of nanovaccines have been employed, among which virus-like nanoparticles (VLPs) and self-assembled peptide nanoparticles (SAPNs) seem very promising. Recently, SAPNs have attracted special interest due to their unique properties, including molecular specificity, biodegradability, and biocompatibility. They also resemble pathogens in terms of their size. Their multivalency allows an orderly repetitive display of antigens on their surface, which induces a stronger immune response than single immunogens. In vaccine design, SAPN self-adjuvanticity is regarded an outstanding advantage, since the use of toxic adjuvants is no longer required. SAPNs are usually composed of helical or β-sheet secondary structures and are tailored from natural peptides or de novo structures. Flexibility in subunit selection opens the door to a wide variety of molecules with different characteristics. SAPN engineering is an emerging area, and more novel structures are expected to be generated in the future, particularly with the rapid progress in related computational tools. The aim of this review is to provide a state-of-the-art overview of self-assembled peptide nanoparticles and their use in vaccine design in recent studies. Additionally, principles for their design and the application of computational approaches to vaccine design are summarized.

Cell membrane-derived nanomaterials for biomedical applications

The continued evolution of biomedical nanotechnology has enabled clinicians to better detect, prevent, manage, and treat human disease. In order to further push the limits of nanoparticle performance and functionality, there has recently been a paradigm shift towards biomimetic design strategies. By taking inspiration from nature, the goal is to create next-generation nanoparticle platforms that can more effectively navigate and interact with the incredibly complex biological systems that exist within the body. Of great interest are cellular membranes, which play essential roles in biointerfacing, self-identification, signal transduction, and compartmentalization. In this review, we explore the major ways in which researchers have directly leveraged cell membrane-derived biomaterials for the fabrication of novel nanotherapeutics and nanodiagnostics. Such emerging technologies have the potential to significantly advance the field of nanomedicine, helping to improve upon traditional modalities while also enabling novel applications.

Self-Assembling Peptide Epitopes as Novel Platform for Anticancer Vaccination

The aim of the present study was to improve the immunogenicity of peptide epitope vaccines using novel nanocarriers based on self-assembling materials. Several studies demonstrated that peptide antigens in nanoparticulate form induce stronger immune responses than their soluble forms. However, several issues such as poor loading and risk of inducing T cell anergy due to premature release of antigenic epitopes have challenged the clinical success of such systems. In the present study, we developed two vaccine delivery systems by appending a self-assembling peptide (Ac-AAVVLLLW-COOH) or a thermosensitive polymer poly(N-isopropylacrylamide (pNIPAm) to the N-terminus of different peptide antigens (OVA250-264, HPV-E743-57) to generate self-assembling peptide epitopes (SAPEs). The obtained results showed that the SAPEs were able to form nanostructures with a diameter from 20 to 200 nm. The SAPEs adjuvanted with CpG induced and expanded antigen-specific CD8+ T cells in mice. Furthermore, tumor-bearing mice vaccinated with SAPEs harboring the HPV E743-57 peptide showed a delayed tumor growth and an increased survival compared to sham-treated mice. In conclusion, self-assembling peptide based systems increase the immunogenicity of peptide epitope vaccines and therefore warrants further development toward clinical use.

Classification of self-assembling protein nanoparticle architectures for applications in vaccine design

We introduce here a mathematical procedure for the structural classification of a specific class of self-assembling protein nanoparticles (SAPNs) that are used as a platform for repetitive antigen display systems. These SAPNs have distinctive geometries as a consequence of the fact that their peptide building blocks are formed from two linked coiled coils that are designed to assemble into trimeric and pentameric clusters. This allows a mathematical description of particle architectures in terms of bipartite (3,5)-regular graphs. Exploiting the relation with fullerene graphs, we provide a complete atlas of SAPN morphologies. The classification enables a detailed understanding of the spectrum of possible particle geometries that can arise in the self-assembly process. Moreover, it provides a toolkit for a systematic exploitation of SAPNs in bioengineering in the context of vaccine design, predicting the density of B-cell epitopes on the SAPN surface, which is critical for a strong humoral immune response.

Role of Metallic Nanoparticles in Vaccinology: Implications for Infectious Disease Vaccine Development

Subunit vaccines are safer but less immunogenic than live-attenuated vaccines or whole cell inactivated vaccines. Adjuvants are used to enhance and modulate antigen (Ag) immunogenicity, aiming to induce a protective and long-lasting immune response. Several molecules and formulations have been studied for their adjuvanticity, but only seven have been approved to formulate human vaccines. Metallic nanoparticles (MeNPs), particularly those containing gold and iron oxides, are widely used in medicine for diagnosis and therapy and have been used as carriers for drugs and vaccines. However, little is known about the immune response elicited by MeNPs or about their importance in the development of new vaccines. There is evidence that these particles display adjuvant characteristics, promoting cell recruitment, antigen-presenting cell activation, cytokine production, and inducing a humoral immune response. This review focuses on the characteristics of MeNPs that could facilitate the induction of a cellular immune response, particularly T-helper 1 and T-helper 17, and their potential functions as adjuvants for subunit vaccines.

The application of self-assembled nanostructures in peptide-based subunit vaccine development

•

Smaller polymer-peptide conjugates-based nanoparticles are often more immunogenic.

•

Lipid-antigen conjugates-based nanoparticles can interact with immune receptors.

•

Peptides with β-sheet conformation usually form nanofibers.

•

α-Helical and random coil peptides tend to self-assemble into nanoparticles.

•

Peptide-based nanostructures are usually poorer inducers of immune responses.

Peptide based-vaccines are becoming one of the most widely investigated prophylactic and therapeutic health care interventions against a variety of diseases, including cancer. However, the lack of a safe and highly efficient adjuvant (immune stimulant) is regarded as the biggest obstacle to vaccine development. The incorporation of a peptide antigen in a nanostructure-based delivery system was recently shown to overcome this obstacle. Nanostructures are often formed from antigens conjugated to molecules such as polymers, lipids, and peptide, with the help of self-assembly phenomenon. This review describes the application of self-assembly process for the production of peptide-based vaccine candidates and the ability of these nanostructures to stimulate humoral and cellular immune responses.

Harnessing supramolecular peptide nanotechnology in biomedical applications

The harnessing of peptides in biomedical applications is a recent hot topic. This arises mainly from the general biocompatibility of peptides, as well as from the ease of tunability of peptide structure to engineer desired properties. The ease of progression from laboratory testing to clinical trials is evident from the plethora of examples available. In this review, we compare and contrast how three distinct self-assembled peptide nanostructures possess different functions. We have 1) nanofibrils in biomaterials that can interact with cells, 2) nanoparticles that can traverse the bloodstream to deliver its payload and also be bioimaged, and 3) nanotubes that can serve as cross-membrane conduits and as a template for nanowire formation. Through this review, we aim to illustrate how various peptides, in their various self-assembled nanostructures, possess great promise in a wide range of biomedical applications and what more can be expected.

Recent advances in self-assembled peptides: Implications for targeted drug delivery and vaccine engineering

Self-assembled peptides have shown outstanding characteristics for vaccine delivery and drug targeting. Peptide molecules can be rationally designed to self-assemble into specific nanoarchitectures in response to changes in their assembly environment including: pH, temperature, ionic strength, and interactions between host (drug) and guest molecules. The resulting supramolecular nanostructures include nanovesicles, nanofibers, nanotubes, nanoribbons, and hydrogels and have a diverse range of mechanical and physicochemical properties. These molecules can be designed for cell-specific targeting by including adhesion ligands, receptor recognition ligands, or peptide-based antigens in their design, often in a multivalent display. Depending on their design, self-assembled peptide nanostructures have advantages in biocompatibility, stability against enzymatic degradation, encapsulation of hydrophobic drugs, sustained drug release, shear-thinning viscoelastic properties, and/or adjuvanting properties. These molecules can also act as intracellular transporters and respond to changes in the physiological environment. Furthermore, this class of materials has shown sequence- and structure-dependent impacts on the immune system that can be tailored to non-immunogenic for drug targeting, and immunogenic for vaccine delivery. This review explores self-assembled peptide nanostructures (beta sheets, alpha helices, peptide amphiphiles, amino acid pairing, elastin like polypeptides, cyclic peptides, short peptides, Fmoc peptides, and peptide hydrogels) and their application in vaccine delivery and drug targeting.

Principles Governing the Self-Assembly of Coiled-Coil Protein Nanoparticles

Self-assembly refers to the spontaneous organization of individual building blocks into higher order structures. It occurs in biological systems such as spherical viruses, which utilize icosahedral symmetry as a guiding principle for the assembly of coat proteins into a capsid shell. In this study, we characterize the self-assembling protein nanoparticle (SAPN) system, which was inspired by such viruses. To facilitate self-assembly, monomeric building blocks have been designed to contain two oligomerization domains. An N-terminal pentameric coiled-coil domain is linked to a C-terminal coiled-coil trimer by two glycine residues. By combining monomers with inherent propensity to form five- and threefold symmetries in higher order agglomerates, the supposition is that nanoparticles will form that exhibit local and global symmetry axes of order 3 and 5. This article explores the principles that govern the assembly of such a system. Specifically, we show that the system predominantly forms according to a spherical core-shell morphology using a combination of scanning transmission electron microscopy and small angle neutron scattering. We introduce a mathematical toolkit to provide a specific description of the possible SAPN morphologies, and we apply it to characterize all particles with maximal symmetry. In particular, we present schematics that define the relative positions of all individual chains in the symmetric SAPN particles, and provide a guide of how this approach can be generalized to nonspherical morphologies, hence providing unprecedented insights into their geometries that can be exploited in future applications.

Symmetry-Directed Design of Protein Cages and Protein Lattices and Their Applications

The assembly of individual protein subunits into large-scale structures is important in many biological contexts. Proteins may assemble into geometrical cages or extended lattices that are characterized by a high degree of symmetry; examples include viral capsids and bacterial S-layers. The precisely defined higher order structure exhibited by these assemblies has inspired efforts to design such structures de novo by applying the principles of symmetry evident in natural protein assemblies. Here we discuss progress towards this goal and also examples of natural protein cages and lattices that have been engineered to repurpose them towards a diverse range of applications in materials science and nano-medicine.

Vaccine Adjuvant Nanotechnologies

The increasing sophistication of vaccine adjuvant design has been driven by improved understanding of the importance of nanoscale features of adjuvants to their immunological function. Newly available advanced nanomanufacturing techniques now allow very precise control of adjuvant particle size, shape, texture, and surface chemistry. Novel adjuvant concepts include self-assembling particles and targeted immune delivery. These individual concepts can be combined to create a single integrated vaccine nanoparticle-combining antigen, adjuvants, and DC-targeting elements. In the process, the concept of an adjuvant has broadened to include not only immune-stimulatory substances but also any design features that enhance the immune response against the relevant vaccine antigen. The modern definition of an adjuvant includes not only classical immune stimulators but also any aspects of particle size, shape, and surface chemistry that enhance vaccine immunogenicity. It even includes purely physical processes such as texturing of particle surfaces to maximize immunogenicity. Looking forward, adjuvants will increasingly be seen not as separate add-on items but as wholly integrated elements of a complete vaccine delivery package. Hence, vaccine systems will increasingly approach the complexity and sophistication of pathogens themselves, incorporating highly specific particle properties, contents, and behaviors, all designed to maximize immune system recognition and drive the immune response in the specific direction that affords maximal protection.

Vaccine technologies: From whole organisms to rationally designed protein assemblies

Vaccines have been the single most significant advancement in public health, preventing morbidity and mortality in millions of people annually. Vaccine development has traditionally focused on whole organism vaccines, either live attenuated or inactivated vaccines. While successful for many different infectious diseases whole organisms are expensive to produce, require culture of the infectious agent, and have the potential to cause vaccine associated disease in hosts. With advancing technology and a desire to develop safe, cost effective vaccine candidates, the field began to focus on the development of recombinantly expressed antigens known as subunit vaccines. While more tolerable, subunit vaccines tend to be less immunogenic. Attempts have been made to increase immunogenicity with the addition of adjuvants, either immunostimulatory molecules or an antigen delivery system that increases immune responses to vaccines. An area of extreme interest has been the application of nanotechnology to vaccine development, which allows for antigens to be expressed on a particulate delivery system. One of the most exciting examples of nanovaccines are rationally designed protein nanoparticles. These nanoparticles use some of the basic tenants of structural biology, biophysical chemistry, and vaccinology to develop protective, safe, and easily manufactured vaccines. Rationally developed nanoparticle vaccines are one of the most promising candidates for the future of vaccine development.

α-Helical coiled-coil peptide materials for biomedical applications

Self-assembling coiled coils, which occur commonly in native proteins, have received significant interest for the design of new biomaterials-based medical therapies. Considerable effort over recent years has led to a detailed understanding of the self-assembly process of coiled coils, and a diverse collection of strategies have been developed for designing functional materials using this motif. The ability to engineer the interface between coiled coils allows one to achieve variously connected components, leading to precisely defined structures such as nanofibers, nanotubes, nanoparticles, networks, gels, and combinations of these. Currently these materials are being developed for a range of biotechnological and medical applications, including drug delivery systems for controlled release, targeted nanomaterials, 'drug-free' therapeutics, vaccine delivery systems, and others. WIREs Nanomed Nanobiotechnol 2017, 9:e1424. doi: 10.1002/wnan.1424 For further resources related to this article, please visit the WIREs website.

Vaccination with self-adjuvanted protein nanoparticles provides protection against lethal influenza challenge

Current influenza vaccines should be improved by the addition of universal influenza vaccine antigens in order to protect against multiple virus strains. We used our self-assembling protein nanoparticles (SAPNs) to display the two conserved influenza antigens M2e and Helix C in their native oligomerization states. To further improve the immunogenicity of the SAPNs, we designed and incorporated the TLR5 agonist flagellin into the SAPNs to generate self-adjuvanted SAPNs. We demonstrate that addition of flagellin does not affect the ability of SAPNs to self-assemble and that they are able to stimulate TLR5 in a dose-dependent manner. Chickens vaccinated with the self-adjuvanted SAPNs induce significantly higher levels of antibodies than those with unadjuvanted SAPNs and show higher cross-neutralizing activity compared to a commercial inactivated virus vaccine. Upon immunization with self-adjuvanted SAPNs, mice were completely protected against a lethal challenge. Thus, we have generated a self-adjuvanted SAPN with a great potential as a universal influenza vaccine.

Molecular Design of a Minimal Peptide Nanoparticle

Nanoparticles are getting a great deal of attention in the rapidly developing field of nanomedicine. For example they can be used as drug delivery systems, for imaging applications, or as carriers for synthetic vaccines. Protein-based nanoparticles offer the advantage of biocompatibility and biodegradability thus avoiding some of the major toxicity concerns with nanoparticle associated approaches. Our group has developed self-assembling peptide/protein nanopartices (SAPNs) that are built up from two coiled-coil oligomerization domains joined by a linker region and used them to design subunit vaccines. For drug delivery approaches the SAPNs need to be as small as possible to avoid strong immune responses that could possibly even lead to anaphylaxis. Here we used a computational and biophysical approach to minimize the size of the SAPNs for their use as drug delivery system. We tested different charge distributions on the pentameric and trimeric coiled-coils in silico with molecular dynamics simulations to down-select an optimal design. This design was then investigated in vitro by biophysical methods and we were able to engineer a minimal SAPN of only 11 nm in diameter. Such minimal-sized SAPNs offer new avenues for a safer development as drug delivery systems or other biomedical applications.

A Method for Producing Protein Nanoparticles with Applications in Vaccines

A practical method is described for synthesizing conjugated protein nanoparticles using thioether (thiol-maleimide) cross-linking chemistry. This method fills the need for a reliable and reproducible synthesis of protein conjugate vaccines for preclinical studies, which can be adapted to produce comparable material for clinical studies. The described method appears to be generally applicable to the production of nanoparticles from a variety of soluble proteins having different structural features. Examples presented include single-component particles of the malarial antigens AMA1, CSP and Pfs25, and two component particles comprised of those antigens covalently cross-linked with the immunogenic carrier protein EPA (a detoxified form of exotoxin A from Pseudomonas aeruginosa). The average molar masses (Mw) of particles in the different preparations ranged from 487 kDa to 3,420 kDa, with hydrodynamic radii (Rh) ranging from 12.1 nm to 38.3 nm. The antigenic properties and secondary structures of the proteins within the particles appear to be largely intact, with no significant changes seen in their far UV circular dichroism spectra, or in their ability to bind conformation-dependent monoclonal antibodies. Mice vaccinated with mixed particles of Pfs25 or CSP and EPA generated significantly greater antigen-specific antibody levels compared with mice vaccinated with the respective unmodified monomeric antigens, validating the potential of antigen-EPA nanoparticles as vaccines.

Design of nanomaterial based systems for novel vaccine development

With lower cell toxicity and higher specificity, novel vaccines have been greatly developed and applied to emerging infectious and chronic diseases. However, due to problems associated with low immunogenicity and complicated processing steps, the development of novel vaccines has been limited. With the rapid development of bio-technologies and material sciences, nanomaterials are playing essential roles in novel vaccine design. Incorporation of nanomaterials is expected to improve delivery efficiency, to increase immunogenicity, and to reduce the administration dosage. The purpose of this review is to discuss the employment of nanomaterials, including polymeric nanoparticles, liposomes, virus-like particles, peptide amphiphiles micelles, peptide nanofibers and microneedle arrays, in vaccine design. Compared to traditional methods, vaccines made from nanomaterials display many appealing benefits, including precise stimulation of immune responses, effective targeting to certain tissue or cells, and desirable biocompatibility. Current research suggests that nanomaterials may improve our approach to the design and delivery of novel vaccines.

Self-assembling protein nanoparticles in the design of vaccines

For over 100 years, vaccines have been one of the most effective medical interventions for reducing infectious disease, and are estimated to save millions of lives globally each year. Nevertheless, many diseases are not yet preventable by vaccination. This large unmet medical need demands further research and the development of novel vaccines with high efficacy and safety. Compared to the 19th and early 20th century vaccines that were made of killed, inactivated, or live-attenuated pathogens, modern vaccines containing isolated, highly purified antigenic protein subunits are safer but tend to induce lower levels of protective immunity. One strategy to overcome the latter is to design antigen nanoparticles: assemblies of polypeptides that present multiple copies of subunit antigens in well-ordered arrays with defined orientations that can potentially mimic the repetitiveness, geometry, size, and shape of the natural host-pathogen surface interactions. Such nanoparticles offer a collective strength of multiple binding sites (avidity) and can provide improved antigen stability and immunogenicity. Several exciting advances have emerged lately, including preclinical evidence that this strategy may be applicable for the development of innovative new vaccines, for example, protecting against influenza, human immunodeficiency virus, and respiratory syncytial virus. Here, we provide a concise review of a critical selection of data that demonstrate the potential of this field. In addition, we highlight how the use of self-assembling protein nanoparticles can be effectively combined with the emerging discipline of structural vaccinology for maximum impact in the rational design of vaccine antigens.

Head-to-Head Comparison of Soluble vs. Qβ VLP Circumsporozoite Protein Vaccines Reveals Selective Enhancement of NANP Repeat Responses

Circumsporozoite protein (CSP) of Plasmodium falciparum is a promising malaria vaccine target. RTS,S, the most advanced malaria vaccine candidate consists of the central NANP repeat and carboxy-terminal region of CSP displayed on a hepatitis B virus-like particle (VLP). To build upon the success of RTS,S, we produced a near full-length Plasmodium falciparum CSP that also includes the conserved amino-terminal region of CSP. We recently showed that this soluble CSP, combined with a synthetic Toll-like-receptor-4 (TLR4) agonist in stable oil-in-water emulsion (GLA/SE), induces a potent and protective immune response in mice against transgenic parasite challenge. Here we have investigated whether the immunogenicity of soluble CSP could be further augmented by presentation on a VLP. Bacteriophage Qβ VLPs can be readily produced in E.coli, they have a diameter of 25 nm and contain packaged E. coli RNA which serves as a built in adjuvant through the activation of TLR7/8. CSP was chemically conjugated to Qβ and the CSP-Qβ vaccine immunogenicity and efficacy were compared to adjuvanted soluble CSP in the C57Bl/6 mouse model. When formulated with adjuvants lacking a TLR4 agonist (Alum, SE and Montanide) the Qβ-CSP induced higher anti-NANP repeat titers, higher levels of cytophilic IgG2b/c antibodies and a trend towards higher protection against transgenic parasite challenge as compared to soluble CSP formulated in the same adjuvant. The VLP and soluble CSP immunogenicity difference was most pronounced at low antigen dose, and within the CSP molecule, the titers against the NANP repeats were preferentially enhanced by Qβ presentation. While a TLR4 agonist enhanced the immunogenicity of soluble CSP to levels comparable to the VLP vaccine, the TLR4 agonist did not further improve the immunogenicity of the Qβ-CSP vaccine. The data presented here pave the way for further improvement in the Qβ conjugation chemistry and evaluation of both the Qβ-CSP and soluble CSP vaccines in the non-human primate model.

The Use of Synthetic Carriers in Malaria Vaccine Design

Malaria vaccine research has been ongoing since the 1980s with limited success. However, recent improvements in our understanding of the immune responses required to combat each stage of infection will allow for intelligent design of both antigens and their associated delivery vaccine vehicles/vectors. Synthetic carriers (also known as vectors) are usually particulate and have multiple properties, which can be varied to control how an associated vaccine interacts with the host, and consequently how the immune response develops. This review comprehensively analyzes both historical and recent studies in which synthetic carriers are used to deliver malaria vaccines. Furthermore, the requirements for a synthetic carrier, such as size, charge, and surface chemistry are reviewed in order to understand the design of effective particle-based vaccines against malaria, as well as providing general insights. Synthetic carriers have the ability to alter and direct the immune response, and a better control of particle properties will facilitate improved vaccine design in the near future.

Design and optimization of peptide nanoparticles

BACKGROUND

Various supra-molecular structures form by self-assembly of proteins in a symmetric fashion. Examples of such structures are viruses, some bacterial micro-compartments and eukaryotic vaults. Peptide/protein-based nanoparticles are emerging in synthetic biology for a variety of biomedical applications, mainly as drug targeting and delivery systems or as vaccines. Our self-assembling peptide nanoparticles (SAPNs) are formed by a single peptide chain that consists of two helical coiled-coil segments connected by a short linker region. One helix is forming a pentameric coiled coil while the other is forming a trimeric coiled coil.

RESULTS

Here, we were studying in vitro and in silico the effect of the chain length and of point mutations near the linker region between the pentamer and the trimer on the self-assembly of the SAPNs. 60 identical peptide chains co-assemble to form a spherical nanoparticle displaying icosahedral symmetry. We have stepwise reduced the size of the protein chain to a minimal chain length of 36 amino acids. We first used biochemical and biophysical methods on the longer constructs followed by molecular dynamics simulations to study eleven different smaller peptide constructs. We have identified one peptide that shows the most promising mini-nanoparticle model in silico.

CONCLUSIONS

An approach of in silico modeling combined with in vitro testing and verification yielded promising peptide designs: at a minimal chain length of only 36 amino acids they were able to self-assemble into proper nanoparticles. This is important since the production cost increases more than linearly with chain length. Also the size of the nanoparticles is significantly smaller than 20 nm, thus reducing the immunogenicity of the particles, which in turn may allow to use the SAPNs as drug delivery systems without the risk of an anaphylactic shock.

Malaria vaccine based on self-assembling protein nanoparticles

Despite recent progress with GSK's RTS,S malaria vaccine, there remains a desperate need for an efficient malaria vaccine. We have used a repetitive antigen display technology to display malaria specific B cell and T cell epitopes in an effort to design a vaccine against Plasmodium falciparum malaria. Our protein sequence when assembled into a nanoparticle induces strong, long-lived and protective immune responses against infection with the parasite. We are confident that the clinical trials with our most developed vaccine candidate will show good protection in a controlled human malaria infection trial.

Particle-based platforms for malaria vaccines

Recombinant subunit vaccines in general are poor immunogens likely due to the small size of peptides and proteins, combined with the lack or reduced presentation of repetitive motifs and missing complementary signal(s) for optimal triggering of the immune response. Therefore, recombinant subunit vaccines require enhancement by vaccine delivery vehicles in order to attain adequate protective immunity. Particle-based delivery platforms, including particulate antigens and particulate adjuvants, are promising delivery vehicles for modifying the way in which immunogens are presented to both the innate and adaptive immune systems. These particle delivery platforms can also co-deliver non-specific immunostimodulators as additional adjuvants. This paper reviews efforts and advances of the Particle-based delivery platforms in development of vaccines against malaria, a disease that claims over 600,000 lives per year, most of them are children under 5 years of age in sub-Sahara Africa.

Multivalent Antigens for Promoting B and T Cell Activation

Efficacious vaccines require antigens that elicit productive immune system activation. Antigens that afford robust antibody production activate both B and T cells. Elucidating the antigen properties that enhance B-T cell communication is difficult with traditional antigens. We therefore used ring-opening metathesis polymerization to access chemically defined, multivalent antigens containing both B and T cell epitopes to explore how antigen structure impacts B cell and T cell activation and communication. The bifunctional antigens were designed so that the backbone substitution level of each antigenic epitope could be quantified using (19)F NMR. The T cell peptide epitope was appended so that it could be liberated in B cells via the action of the endosomal protease cathepsin D, and this design feature was critical for T cell activation. Antigens with high BCR epitope valency induce greater BCR-mediated internalization and T cell activation than did low valency antigens, and these high-valency polymeric antigens were superior to protein antigens. We anticipate that these findings can guide the design of more effective vaccines.

Supramolecular peptide vaccines: tuning adaptive immunity

Successful immunotherapies must be designed to elicit targeted immune responses having a specifiable phenotype across many dimensions, including the phenotypes of T cells, B cells, antigen-presenting cells, and others. For synthetic or subunit vaccines, stimulation of strong enough immune responses usually requires adjuvants, which can cause local inflammation and complicate the targeting of such phenotypes. Supramolecular materials provide routes for reducing or eliminating supplemental adjuvants. Owing to their compositional controllability, supramolecular assemblies show promise for fine-tuning immune responses by adjusting combinations of material attributes including epitope content, multivalency, size, dose, and small quantities of specific adjuvants. Here we focus on supramolecular vaccines incorporating multiple epitopes in precise ratios, with an emphasis on peptides that form high-aspect ratio (i.e. fibrillar) structures.

Nano-Synthetic Devices in Leishmaniasis: A Bioinformatics Approach

Synthetic biology is an investigative and constructive means of understanding the complexities of biology. Substantial progress in the fields has resulted in the creation of synthetic gene circuits, which when uploaded into the appropriate nanoliposomal vehicle, can be used for a tunable response in a cell. These tunable elements can be applied to treat diseased condition for a transition to a healthy state. Though in its nascent stage of development synthetic biology is beginning to use its constructs to bring engineering approaches into biomedicine for treatment of infectious disease leishmaniasis.

Optimizing the design of protein nanoparticles as carriers for vaccine applications

Successful vaccine development remains a huge challenge for infectious diseases such as malaria, HIV and influenza. As a novel way to present antigenic epitopes to the immune system, we have developed icosahedral self-assembling protein nanoparticles (SAPNs) to serve as a prototypical vaccine platform for infectious diseases. Here we examine some biophysical factors that affect the self-assembly of these nanoparticles, which have as basic building blocks coiled-coil oligomerization domains joined by a short linker region. Relying on in silico computer modeling predictions, we selected five different linker regions from the RCSB protein database that connect oligomerization domains, and then further studied the self-assembly and stability of in vitro produced nanoparticles through biophysical characterization of formed particles. One design in particular, T2i88, revealed excellent self-assembly and homogeneity thus paving the way toward a more optimized nanoparticle for vaccine applications.

From the Clinical Editor

Despite the widespread use of vaccines worldwide, successful development of vaccines against some diseases remains a challenge still. In this article, the authors investigated the physic-chemical and biological properties of icosahedral self-assembling protein nanoparticles (SAPNs), which mimic viral particles, in order to utilize this technology as potential platform for future design of vaccines.

Guiding principles in the design of molecular bioconjugates for vaccine applications

Antigen- and adjuvant-based bioconjugates that can stimulate the immune system play an important role in vaccine applications. Bioconjugates have demonstrated unique physicochemical and biological properties, enabling vaccines to be delivered to key immune cells, to target specific intracellular pathways, or to mimic immunogenic properties of natural pathogens. In this Review we highlight recent advances in such molecular immunomodulators, with an emphasis on the structure-function relationships that provide the foundation for rational design of safe and effective vaccines and immunotherapies.

A silk purse from a sow's ear-bioinspired materials based on α-helical coiled coils

This past few years have heralded remarkable times for intermediate filaments with new revelations of their structural properties that has included the first crystallographic-based model of vimentin to build on the experimental data of intra-filament interactions determined by chemical cross-linking. Now with these and other advances on their assembly, their biomechanical and their cell biological properties outlined in this review, the exploitation of the biomechanical and structural properties of intermediate filaments, their nanocomposites and biomimetic derivatives in the biomedical and private sectors has started.

Recent advances in peptide-based subunit nanovaccines

Vaccination is the most efficient way to protect humans against pathogens. Peptide-based vaccines offer several advantages over classical vaccines, which utilized whole organisms or proteins. However, peptides alone are not immunogenic and need a delivery system that can boost their recognition by the immune system. In recent years, nanotechnology-based approaches have become one of the most promising strategies in peptide vaccine delivery. This review summarizes knowledge on peptide vaccines and nanotechnology-based approaches for their delivery. The recently reported nano-sized delivery platforms for peptide antigens are reviewed, including nanoparticles composed of polymers, peptides, lipids, inorganic materials and nanotubes. The future prospects for peptide-based nanovaccines are discussed.

Titrating T-cell epitopes within self-assembled vaccines optimizes CD4+ helper T cell and antibody outputs

Epitope content plays a critical role in determining T-cell and antibody responses to vaccines, biomaterials, and protein therapeutics, but its effects are nonlinear and difficult to isolate. Here, molecular self-assembly is used to build a vaccine with precise control over epitope content, in order to finely tune the magnitude and phenotype of T helper and antibody responses. Self-adjuvanting peptide nanofibers are formed by co-assembling a high-affinity universal CD4+ T-cell epitope (PADRE) and a B-cell epitope from Staphylococcus aureus at specifiable concentrations. Increasing the PADRE concentration from micromolar to millimolar elicited bell-shaped dose-responses that are unique to different T-cell populations. Notably, the epitope ratios that maximize T follicular helper and antibody responses differed by an order of magnitude from those that maximized Th1 or Th2 responses. Thus, modular materials assembly provides a means of controlling epitope content and efficiently skewing the adaptive immune response in the absence of exogenous adjuvant; this approach may contribute to the development of improved vaccines and immunotherapies.

Nanomedicine in the Management of Microbial Infection - Overview and Perspectives

For more than 2 billion years, microbes have reigned on our planet, evolving or outlasting many obstacles they have encountered. In the 20th century, this trend took a dramatic turn with the introduction of antibiotics and vaccines. Nevertheless, since then, microbes have progressively eroded the effectiveness of previously successful antibiotics by developing resistance, and many infections have eluded conventional vaccine design approaches. Moreover, the emergence of resistant and more virulent strains of bacteria has outpaced the development of new antibiotics over the last few decades. These trends have had major economic and health impacts at all levels of the socioeconomic spectrum - we need breakthrough innovations that could effectively manage microbial infections and deliver solutions that stand the test of time. The application of nanotechnologies to medicine, or nanomedicine, which has already demonstrated its tremendous impact on the pharmaceutical and biotechnology industries, is rapidly becoming a major driving force behind ongoing changes in the antimicrobial field. Here we provide an overview on the current progress of nanomedicine in the management of microbial infection, including diagnosis, antimicrobial therapy, drug delivery, medical devices, and vaccines, as well as perspectives on the opportunities and challenges in antimicrobial nanomedicine.

Engaging adaptive immunity with biomaterials

Adaptive immune responses, characterized by T cells and B cells engaging and responding to specific antigens, can be raised by biomaterials containing proteins, peptides, and other biomolecules. How does one avoid, control, or exploit such responses? This review will discuss major properties and processes that influence biomaterials-directed adaptive immunity, including the physical dimensions of a material, its epitope content, and its multivalency. Selected strategies involving novel biomaterials designs will be discussed to illustrate these points of control. Specific immunological processes that biomaterials are being developed to direct will be highlighted, including minimally inflammatory scaffolds for tissue repair and immunotherapies eliciting desired B cell (antibody) responses, T cell responses, or tolerance. The continuing development of a knowledge base for specifying the strength and phenotype of biomaterials-mediated adaptive immune responses is important, not only for the engineering of better vaccines and immunotherapies, but also for managing immune responses against newer generations of increasingly biological and biomolecular materials in contexts such as tissue repair, tissue engineering, or cell delivery.

Effectiveness of a novel immunogenic nanoparticle platform for Toxoplasma peptide vaccine in HLA transgenic mice

We created and produced a novel self-assembling nanoparticle platform for delivery of peptide epitopes that induces CD8(+) and CD4(+)T cells that are protective against Toxoplasma gondii infection. These self-assembling polypeptide nanoparticles (SAPNs) are composed of linear peptide (LP) monomers which contain two coiled-coil oligomerization domains, the dense granule 7 (GRA720-28 LPQFATAAT) peptide and a universal CD4(+)T cell epitope (derived from PADRE). Purified LPs assemble into nanoparticles with icosahedral symmetry, similar to the capsids of small viruses. These particles were evaluated for their efficacy in eliciting IFN-γ by splenocytes of HLA-B*0702 transgenic mice and for their ability to protect against subsequent T. gondii challenge. This work demonstrates the feasibility of using this platform approach with a CD8(+) epitope that binds HLA-B7 and tests the biological activity of potentially protective peptides restricted by human major histocompatibility complex (HLA) class I molecules in HLA transgenic mice.

Immunological principles regulating immunomodulation with biomaterials

The immune system has evolved to recognize and eliminate pathogens; this recognition relies on the identification of structural molecular patterns within unique tissue microenvironments. Therefore, bioengineers can harness these immunological cues to design materials that modulate innate and adaptive immunity in a controlled manner. This review acts as an immunology primer by focusing on the basic molecular and cellular immunology principles governing immunomodulation with biomaterials.

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.

Modified dipeptide-based nanoparticles: vehicles for targeted tumor drug delivery

Aim: Different nanoparticles have been investigated to deliver chemotherapeutic agents, but complex synthesis procedures and biocompatibility issues raise concerns in developing them for safe human usage. The aim of this work is to develop α,β-dehydrophenylalanine-containing, self-assembled, amphipathic dipeptide nanoparticles for tumor-targeted drug delivery and therapy. Material & methods: Solution-phase peptide synthesis was used to synthesize dipeptides. Nanoparticles were prepared by molecular self-assembly. A tumor distribution study was carried out using a radiolabeling method. Tumor regression studies were carried out in murine ascitic tumors in BALB/c mice and breast tumor xenografts in in nonobese diabetic/severe combined immuno¬deficiency mice. Results: Arg–α,β-dehydrophenylalanine formed self-assembled nanoparticles that could be easily derivatized with folic acid. Folic acid-derivatized nanoparticles showed enhanced cellular uptake and, when loaded with doxorubicin, showed enhanced tumor regression compared with underivatized nanoparticles or native drug, without any adverse side effects, both in vitro and in vivo.

Original submitted 20 April 2012; Revised submitted 9 November 2012

The biodistribution of self-assembling protein nanoparticles shows they are promising vaccine platforms

BACKGROUND

Because of the need to limit side-effects, nanoparticles are increasingly being studied as drug-carrying and targeting tools. We have previously reported on a scheme to produce protein-based self-assembling nanoparticles that can act as antigen display platforms. Here we attempted to use the same system for cancer-targeting, making use of a C-terminal bombesin peptide that has high affinity for a receptor known to be overexpressed in certain tumors, as well as an N-terminal polyhistidine tag that can be used for radiolabeling with technetium tricarbonyl.

RESULTS

In order to increase circulation time, we experimented with PEGylated and unPEGylated varities typo particle. We also tested the effect of incorporating different numbers of bombesins per nanoparticle. Biophysical characterization determined that all configurations assemble into regular particles with relatively monodisperse size distributions, having peaks of about 33-36 nm. The carbonyl method used for labeling produced approximately 80% labeled nanoparticles. In vitro, the nanoparticles showed high binding, both specific and non-specific, to PC-3 prostate cancer cells. In vivo, high uptake was observed for all nanoparticle types in the spleens of CD-1 nu/nu mice, decreasing significantly over the course of 24 hours. High uptake was also observed in the liver, while only low uptake was seen in both the pancreas and a tumor xenograft.

CONCLUSIONS

The data suggest that the nanoparticles are non-specifically taken up by the reticuloendothelial system. Low uptake in the pancreas and tumor indicate that there is little or no specific targeting. PEGylation or increasing the amount of bombesins per nanoparticle did not significantly improve targeting. In particular, the uptake in the spleen, which is a primary organ of the immune system, highlights the potential of the nanoparticles as vaccine carriers. Also, the decrease in liver and spleen radioactivity with time implies that the nanoparticles are broken down and cleared. This is an important finding, as it shows that the nanoparticles can be safely used as a vaccine platform without the risk of prolonged side effects. Furthermore, it demonstrates that technetium carbonyl radiolabeling of our protein-based nanoparticles can be used to evaluate their pharmacokinetic properties in vivo.

Single-dose microparticle delivery of a malaria transmission-blocking vaccine elicits a long-lasting functional antibody response

Malaria sexual stage and mosquito transmission-blocking vaccines (SSM-TBV) have recently gained prominence as a necessary tool for malaria eradication. SSM-TBVs are unique in that, with the exception of parasite gametocyte antigens, they primarily target parasite or mosquito midgut surface antigens expressed only inside the mosquito. As such, the primary perceived limitation of SSM-TBVs is that the absence of natural boosting following immunization will limit its efficacy, since the antigens are never presented to the human immune system. An ideal, safe SSM-TBV formulation must overcome this limitation. We provide a focused evaluation of relevant nano-/microparticle technologies that can be applied toward the development of leading SSM-TBV candidates, and data from a proof-of-concept study demonstrating that a single inoculation and controlled release of antigen in mice, can elicit long-lasting protective antibody titers. We conclude by identifying the remaining critical gaps in knowledge and opportunities for moving SSM-TBVs to the field.

Applications of nanotechnology for immunology

Nanotechnology uses the unique properties of objects that function as a unit within the overall size range of 1-1,000 nanometres. The engineering of nanostructure materials, including nanoparticles, nanoemulsions or nanotubules, holds great promise for the development of new immunomodulatory agents, as such nanostructures can be used to more effectively manipulate or deliver immunologically active components to target sites. Successful applications of nanotechnology in the field of immunology will enable new generations of vaccines, adjuvants and immunomodulatory drugs that aim to improve clinical outcomes in response to a range of infectious and non-infectious diseases.

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

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

Report from the field: Overview of the Sixth Annual Vaccine Renaissance Conference

The Sixth Annual Vaccine Renaissance Conference, hosted by the Institute for Immunology and Informatics (iCubed) at the University of Rhode Island (URI), took place on October 15-17, 2012. This conference provides a forum for the review of current progress in the discovery and development of vaccines, and creates an environment for the exchange of ideas. Dr. Joel McCleary opened the conference with a warning about the importance of preparing for well-defined biowarfare threats, including tularemia and Staphylococcal enterotoxin B. Following the keynote address, sessions explored biodefense and preparation for pandemic and biowarfare threats; vaccines for emerging and re-emerging neglected tropical diseases; animal vaccines and human health; and vaccine vectors and the human microbiome. In this issue of Human Vaccines and Immunotherapeutics, seven Vaccine Renaissance Conference speakers will showcase their work; here, we describe a few of the conference highlights.

Mechanisms of protective immune responses induced by the Plasmodium falciparum circumsporozoite protein-based, self-assembling protein nanoparticle vaccine

Background

A lack of defined correlates of immunity for malaria, combined with the inability to induce long-lived sterile immune responses in a human host, demonstrate a need for improved understanding of potentially protective immune mechanisms for enhanced vaccine efficacy. Protective sterile immunity (>90%) against the Plasmodium falciparum circumsporozoite protein (CSP) has been achieved using a transgenically modified Plasmodium berghei sporozoite (Tg-Pb/PfCSP) and a self-assembling protein nanoparticle (SAPN) vaccine presenting CSP epitopes (PfCSP-SAPN). Here, several possible mechanisms involved in the independently protective humoral and cellular responses induced following SAPN immunization are described.

Methods

Inbred mice were vaccinated with PfCSP-SAPN in PBS. Serum antibodies were harvested and effects on P. falciparum sporozoites mobility and integrity were examined using phase contrast microscopy. The functionality of SAPN-induced antibodies on inhibition of sporozoite invasion and growth within primary human hepatocytes was also examined. The internal processing of SAPN by bone marrow-derived dendritic cells (BMDDC), using organelle-specific, fluorescent-tagged antibody or gold-encapsulated SAPN, was observed using confocal or electron microscopy, respectively.

Results

The results of this work demonstrate that PfCSP-SAPN induces epitope-specific antibody titers, predominantly of the Th2 isotype IgG1, and that serum antibodies from PfCSP-SAPN-immunized mice appear to target P. falciparum sporozoites via the classical pathway of complement. This results in sporozoite death as indicated by cessation of motility and the circumsporozoite precipitation reaction. Moreover, PfCSP-SAPN-induced antibodies are able to inhibit wild-type P. falciparum sporozoite invasion and growth within cultured primary human hepatocytes. In addition, the observation that PfCSP-SAPN are processed (and presented) to the immune system by dendritic cells in a slow and continuous fashion via transporter associated with antigen processing (TAP) recruitment to the early endosome (EE), and have partially delayed processing through the endoplasmic reticulum, has the potential to induce the long-lived, effector memory CD8⁺ T-cells as described previously.

Conclusion

This paper describes the examination of humoral and cellular immune mechanisms induced by PfCSP-SAPN vaccination which result in sterile host protection against a transgenic P. berghei malaria sporozoite expressing the P. falciparum CSP, and which significantly inhibits native P. falciparum sporozoites from invading and developing within cultured human hepatocytes. These results may indicate the type and mode of action of protective antibodies needed to control P. falciparum sporozoites from infecting humans as well as a potential mechanism of induction of protective long-lived effector memory CD8⁺ T-cells.

Expression, purification and refolding of a self-assembling protein nanoparticle (SAPN) malaria vaccine

There are many ways to present antigens to the immune system. We have used a repetitive antigen display technology that relies on the self-assembly of 60 protein chains into a spherical self-assembling protein nanoparticle (SAPN) to develop a vaccine against Plasmodium falciparum malaria. The protein sequence contains selected B- and T-cell epitopes of the circumsporozoite protein of P. falciparum (PfCSP) and, when assembled into a nanoparticle induces strong, long-lived and protective immune responses against the PfCSP. Here we describe the conditions needed for promoting self-assembly of a P. falciparum vaccine nanoparticle, PfCSP-KMY-SAPN, and note pitfalls that may occur when determining conditions for other SAPN vaccines. Attention was paid to selecting processes that were amenable to scale up and cGMP manufacturing.

Plasmodium falciparum synthetic LbL microparticle vaccine elicits protective neutralizing antibody and parasite-specific cellular immune responses

Epitopes of the circumsporozoite (CS) protein of Plasmodium falciparum, the most pathogenic species of the malaria parasite, have been shown to elicit protective immunity in experimental animals and human volunteers. The mechanisms of immunity include parasite-neutralizing antibodies that can inhibit parasite motility in the skin at the site of infection and in the bloodstream during transit to the hepatocyte host cell and also block interaction with host cell receptors on hepatocytes. In addition, specific CD4+ and CD8+ cellular mechanisms target the intracellular hepatic forms, thus preventing release of erythrocytic stage parasites from the infected hepatocyte and the ensuing blood stage cycle responsible for clinical disease. An innovative method for producing particle vaccines, layer-by-layer (LbL) fabrication of polypeptide films on solid CaCO3 cores, was used to produce synthetic malaria vaccines containing a tri-epitope CS peptide T1BT comprising the antibody epitope of the CS repeat region (B) and two T-cell epitopes, the highly conserved T1 epitope and the universal epitope T. Mice immunized with microparticles loaded with T1BT peptide developed parasite-neutralizing antibodies and malaria-specific T-cell responses including cytotoxic effector T-cells. Protection from liver stage infection following challenge with live sporozoites from infected mosquitoes correlated with neutralizing antibody levels. Although some immunized mice with low or undetectable neutralizing antibodies were also protected, depletion of T-cells prior to challenge resulted in the majority of mice remaining resistant to challenge. In addition, mice immunized with microparticles bearing only T-cell epitopes were not protected, demonstrating that cellular immunity alone was not sufficient for protective immunity. Although the microparticles without adjuvant were immunogenic and protective, a simple modification with the lipopeptide TLR2 agonist Pam3Cys increased the potency and efficacy of the LbL vaccine candidate. This study demonstrates the potential of LbL particles as promising malaria vaccine candidates using the T1BT epitopes from the P. falciparum CS protein.

Nanoscale assemblies and their biomedical applications

Nanoscale assemblies are a unique class of materials, which can be synthesized from inorganic, polymeric or biological building blocks. The multitude of applications of this class of materials ranges from solar and electrical to uses in food, cosmetics and medicine. In this review, we initially highlight characteristic features of polymeric nanoscale assemblies as well as those built from biological units (lipids, nucleic acids and proteins). We give special consideration to protein nanoassemblies found in nature such as ferritin protein cages, bacterial microcompartments and vaults found in eukaryotic cells and designed protein nanoassemblies, such as peptide nanofibres and peptide nanotubes. Next, we focus on biomedical applications of these nanoscale assemblies, such as cell targeting, drug delivery, bioimaging and vaccine development. In the vaccine development section, we report in more detail the use of virus-like particles and self-assembling polypeptide nanoparticles as new vaccine delivery platforms.