Injectable tissue integrating networks from recombinant polypeptides with tunable order

Emergent properties of natural biomaterials result from the collective effects of nanoscale interactions among ordered and disordered domains. Here, using recombinant sequence design, we have created a set of partially ordered polypeptides to study emergent hierarchical structures by precisely encoding nanoscale order-disorder interactions. These materials, which combine the stimuli-responsiveness of disordered elastin-like polypeptides and the structural stability of polyalanine helices, are thermally responsive with tunable thermal hysteresis and the ability to reversibly form porous, viscoelastic networks above threshold temperatures. Through coarse-grain simulations, we show that hysteresis arises from physical crosslinking due to mesoscale phase separation of ordered and disordered domains. On injection of partially ordered polypeptides designed to transition at body temperature, they form stable, porous scaffolds that rapidly integrate into surrounding tissue with minimal inflammation and a high degree of vascularization. Sequence-level modulation of structural order and disorder is an untapped principle for the design of functional protein-based biomaterials.

Author Correction: Injectable tissue integrating networks from recombinant polypeptides with tunable order

In the version of this Article originally published, one of the authors' names was incorrectly given as Jeffery Schaal; it should have been Jeffrey L. Schaal. This has been corrected in all versions of the Article.

Self-Assembling Peptide Gels for 3D Prostate Cancer Spheroid Culture

Progress in prostate cancer research is presently limited by a shortage of reliable in vitro model systems. The authors describe a novel self-assembling peptide, bQ13, which forms nanofibers and gels useful for the 3D culture of prostate cancer spheroids, with improved cytocompatibility compared to related fibrillizing peptides. The mechanical properties of bQ13 gels can be controlled by adjusting peptide concentration, with storage moduli ranging between 1 and 10 kPa. bQ13's ability to remain soluble at mildly basic pH considerably improved the viability of encapsulated cells compared to other self-assembling nanofiber-forming peptides. LNCaP cells formed spheroids in bQ13 gels with similar morphologies and sizes to those formed in Matrigel or RADA16-I. Moreover, prostate-specific antigen (PSA) is produced by LNCaP cells in all matrices, and PSA production is more responsive to enzalutamide treatment in bQ13 gels than in other fibrillized peptide gels. bQ13 represents an attractive platform for further tailoring within 3D cell culture systems.

Intranasal delivery of adjuvant-free peptide nanofibers elicits resident CD8+ T cell responses

Influenza vaccines that can be administered intranasally or by other needle-free delivery routes have potential advantages over injected formulations in terms of patient compliance, cost, and ease of global distribution. Supramolecular peptide nanofibers have been investigated previously as platforms for vaccines and immunotherapies and have been shown to raise immune responses in the absence of exogenous adjuvants and without measurable inflammation. However, at present it has not been tested whether the immunogenicity of these materials extends to the intranasal route. Here we investigated the extent to which self-assembled peptide nanofibers bearing an influenza peptide epitope elicit antigen-specific CD8+ T cell responses when delivered intranasally, and we compared these responses with those elicited by subcutaneous immunization. Peptides containing an epitope from influenza acid polymerase (PA) and the Q11 self-assembly domain formed nanofibers that were avidly taken up by dendritic cells in lung-draining mediastinal lymph nodes after intranasal immunization. Intranasally delivered nanofibers generated greater antigen-specific CD8+ T cell responses in the lung-draining lymph nodes than subcutaneous immunizations while retaining the non-inflammatory character of the materials observed in other delivery sites. The CD8+ T cells elicited systemically were functional as assessed by their ability to produce IFN-γ ex vivo, lyse epitope-pulsed target cells in vivo, and diminish viral loads in infected mice. Compared to subcutaneously delivered nanofibers, intranasally delivered peptide nanofibers significantly increased the number of persisting antigen-specific tissue resident memory CD8+ T cells in the lung, allowing for a more rapid response to infection at 6 weeks post-vaccination. These results indicate that intranasally delivered self-assembled peptide nanofibers are immunogenic when delivering CD8+ epitopes without adjuvant or CD4+ epitopes, are non-inflammatory, and promote more lung-resident memory CD8+ T cells compared to subcutaneous immunization.

Progress Toward the Clinical Translation of Bioinspired Peptide and Protein Assemblies

Supramolecular materials composed of proteins and peptides have been receiving considerable attention toward a range of diseases and conditions from vaccines to drug delivery. Owing to the relative newness of this class of materials, the bulk of work to date has been preclinical. However, examples of approved treatments particularly in vaccines, dentistry, and hemostasis demonstrate the translational potential of supramolecular polypeptides. Critical milestones in the clinical development of this class of materials and currently approved supramolecular polypeptide therapies are described in this study. Additional examples of not-yet-approved materials that are steadily advancing toward clinical use are also featured. Spherical assemblies such as virus-like particles, designed protein nanoparticles, and spherical peptide amphiphiles are highlighted, followed by fiber-forming systems such as fibrillizing peptides, fiber-forming peptide-amphiphiles, and filamentous bacteriophages.

Practical Considerations in the Design and Use of Immunologically Active Fibrillar Peptide Assemblies

The design, formulation, and immunological evaluation of self-assembling peptide materials is relatively straightforward. Indeed, one of the advantages of synthetic self-assembling peptides is that one can progress from initial concept to in vivo testing in a matter of days. However, because these materials are supramolecular, working with them is not without some practical challenges, and subtle changes in design, synthesis, handling, and formulation can affect the materials' immunogenicity. This chapter is intended to communicate some of these practical aspects of working with these materials that are not always enumerated in conventional research papers. Epitope considerations, peptide synthesis, purification, storage, nanofiber formation, quality control, immunological evaluation, and the overall phenotypic characteristics of the immune responses to be expected from these materials are discussed.

Active immunotherapy for TNF-mediated inflammation using self-assembled peptide nanofibers

Active immunotherapies raising antibody responses against autologous targets are receiving increasing interest as alternatives to the administration of manufactured antibodies. The challenge in such an approach is generating protective and adjustable levels of therapeutic antibodies while at the same time avoiding strong T cell responses that could lead to autoimmune reactions. Here we demonstrate the design of an active immunotherapy against TNF-mediated inflammation using short synthetic peptides that assemble into supramolecular peptide nanofibers. Immunization with these materials, without additional adjuvants, was able to break B cell tolerance and raise protective antibody responses against autologous TNF in mice. The strength of the anti-TNF antibody response could be tuned by adjusting the epitope content in the nanofibers, and the T-cell response was focused on exogenous and non-autoreactive T-cell epitopes. Immunization with unadjuvanted peptide nanofibers was therapeutic in a lethal model of acute inflammation induced by intraperitoneally delivered lipopolysaccharide, whereas formulations adjuvanted with CpG showed comparatively poorer protection that correlated with a more Th1-polarized response. Additionally, immunization with peptide nanofibers did not diminish the ability of mice to clear infections of Listeria monocytogenes. Collectively this work suggests that synthetic self-assembled peptides can be attractive platforms for active immunotherapies against autologous targets.

A Supramolecular Vaccine Platform Based on α-Helical Peptide Nanofibers

A supramolecular peptide vaccine system was designed in which epitope-bearing peptides self-assemble into elongated nanofibers composed almost entirely of alpha-helical structure. The nanofibers were readily internalized by antigen presenting cells and produced robust antibody, CD4+ T-cell, and CD8+ T-cell responses without supplemental adjuvants in mice. Epitopes studied included a cancer B-cell epitope from the epidermal growth factor receptor class III variant (EGFRvIII), the universal CD4+ T-cell epitope PADRE, and the model CD8+ T-cell epitope SIINFEKL, each of which could be incorporated into supramolecular multi-epitope nanofibers in a modular fashion.

Biomaterial strategies for generating therapeutic immune responses

Biomaterials employed to raise therapeutic immune responses have become a complex and active field. Historically, vaccines have been developed primarily to fight infectious diseases, but recent years have seen the development of immunologically active biomaterials towards an expanding list of non-infectious diseases and conditions including inflammation, autoimmunity, wounds, cancer, and others. This review structures its discussion of these approaches around a progression from single-target strategies to those that engage increasingly complex and multifactorial immune responses. First, the targeting of specific individual cytokines is discussed, both in terms of delivering the cytokines or blocking agents, and in terms of active immunotherapies that raise neutralizing immune responses against such single cytokine targets. Next, non-biological complex drugs such as randomized polyamino acid copolymers are discussed in terms of their ability to raise multiple different therapeutic immune responses, particularly in the context of autoimmunity. Last, biologically derived matrices and materials are discussed in terms of their ability to raise complex immune responses in the context of tissue repair. Collectively, these examples reflect the tremendous diversity of existing approaches and the breadth of opportunities that remain for generating therapeutic immune responses using biomaterials.

Switching the Immunogenicity of Peptide Assemblies Using Surface Properties

Biomaterials created from supramolecular peptides, proteins, and their derivatives have been receiving increasing interest for both immunological applications, such as vaccines and immunotherapies, as well as ostensibly nonimmunological applications, such as therapeutic delivery or tissue engineering. However, simple rules for either maximizing immunogenicity or abolishing it have yet to be elucidated, even though immunogenicity is a prime consideration for the design of any supramolecular biomaterial intended for use in vivo. Here, we investigated a range of physicochemical properties of fibrillized peptide biomaterials, identifying negative surface charge as a means for completely abolishing antibody and T cell responses against them in mice, even when they display a competent epitope. The work was facilitated by the modularity of the materials, which enabled the generation of a set of co-assembled fibrillar peptide materials with broad ranges of surface properties. It was found that negative surface charge, provided via negatively charged amino acid residues, prevented T cell and antibody responses to antigen-carrying assemblies because it prevented uptake of the materials by antigen-presenting cells (APCs), which in turn prevented presentation of the epitope peptide in the APCs' major histocompatibility class II molecules. Conversely, positive surface charge augmented the uptake of fibrillized peptides by APCs. These findings suggest that some surface characteristics, such as extensive negative charge, should be avoided in vaccine design using supramolecular peptide assemblies. More importantly, it provides a strategy to switch off potentially problematic immunogenicity for using these materials in nonimmunological applications.

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.

This paper is the winner of an SFB Award in the Hospital Intern, Residency category: Peptide biomaterials raising adaptive immune responses in wound healing contexts

Biomaterials used in the context of tissue engineering or wound repair are commonly designed to be "nonimmunogenic." However, previously it has been observed that self-assembled peptide nanofiber materials are noninflammatory despite their immunogenicity, suggesting that they may be appropriate for use in wound-healing contexts. To test this hypothesis, mice were immunized with epitope-containing peptide self-assemblies until they maintained high antibody titers against the material, then gels of the same peptide assemblies were applied within full-thickness dermal wounds. In three different murine dermal-wounding models with different baseline healing rates, even significantly immunogenic peptide assemblies did not delay healing. Conversely, adjuvanted peptide assemblies, while raising similar antibody titers to unadjuvanted assemblies, did delay wound healing. Analysis of the healing wounds indicated that compared to adjuvanted peptide assemblies, the unadjuvanted assemblies exhibited a progression of the dominant T-cell subset from CD4(+) to CD8(+) cells in the wound, and CD4(+) cell populations displayed a more Th2-slanted response. These findings illustrate an example of a significant antibiomaterial adaptive immune response that does not adversely affect wound healing despite ongoing antibody production. This material would thus be considered "immunologically compatible" in this specific context rather than "nonimmunogenic," a designation that is expected to apply to a range of other protein- and peptide-based biomaterials in wound-healing and tissue-engineering applications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1853-1862, 2016.

Thermal stability of self-assembled peptide vaccine materials

The majority of current vaccines depend on a continuous "cold chain" of storage and handling between 2 and 8°C. Vaccines experiencing temperature excursions outside this range can suffer from reduced potency. This thermal sensitivity results in significant losses of vaccine material each year and risks the administration of vaccines with diminished protective ability, issues that are heightened in the developing world. Here, using peptide self-assemblies based on the fibril-forming peptide Q11 and containing the epitopes OVA323-339 from ovalbumin or ESAT651-70 from Mycobacterium tuberculosis, the chemical, conformational, and immunological stability of supramolecular peptide materials were investigated. It was expected that these materials would exhibit advantageous thermal stability owing to their adjuvant-free and fully synthetic construction. Neither chemical nor conformational changes were observed for either peptide when stored at 45°C for 7days. ESAT651-70-Q11 was strongly immunogenic whether it was stored as a dry powder or as aqueous nanofibers, showing undiminished immunogenicity even when stored as long as six months at 45°C. This result was in contrast to ESAT651-70 conjugated to a protein carrier and adjuvanted with alum, which demonstrated marked thermal sensitivity in these conditions. Antibody titers and affinities were undiminished in mice for OVA323-339-Q11 if it was stored as assembled nanofibers, yet some diminishment was observed for material stored as a dry powder. The OVA study was done in a different mouse strain and with a different prime/boost regimen, and so it should not be compared directly with the study for the ESAT epitope. This work indicates that peptide self-assemblies can possess attractive thermal stability properties in the context of vaccine development.

STATEMENT OF SIGNIFICANCE

Almost all current vaccines must be maintained within a tight and refrigerated temperature range, usually between 2 and 8°C. This presents significant challenges for their distribution, especially in the developing world. Here we report on the surprisingly robust thermal stability of a self-assembled peptide vaccine. In particular a self-assembled peptide vaccine containing a tuberculosis epitope maintained all of its potency in mice when exposed to an extreme thermal treatment of six months at 45°C. In a different mouse model, we investigated another model epitope and found some storage conditions where potency was diminished. Overall this study illustrates that some self-assembled peptide vaccines can have remarkable thermal stability.

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.

Self-assembled glycopeptide nanofibers as modulators of galectin-1 bioactivity

Galectins are carbohydrate-binding proteins that act as extracellular signaling molecules in various normal and pathological processes. Galectin bioactivity is mediated by specific non-covalent interactions with cell-surface and extracellular matrix (ECM) glycoproteins, which can enhance or inhibit signaling events that influence various cellular behaviors, including adhesion, proliferation, differentiation, and apoptosis. Here, we developed a materials approach to modulate galectin bioactivity by mimicking natural galectin-glycoprotein interactions. Specifically, we created a variant of a peptide that self-assembles into β-sheet nanofibers under aqueous conditions, QQKFQFQFEQQ (Q11), which has an asparagine residue modified with the monosaccharide N-acetylglucosamine (GlcNAc) at its N-terminus (GlcNAc-Q11). GlcNAc-Q11 self-assembled into β-sheet nanofibers under similar conditions as Q11. Nanofibrillar GlcNAc moieties were efficiently converted to the galectin-binding disaccharide N-acetyllactosamine (LacNAc) via the enzyme β-1,4-galactosyltransferase and the sugar donor UDP-galactose, while retaining β-sheet structure and nanofiber morphology. LacNAc-Q11 nanofibers bound galectin-1 and -3 in a LacNAc concentration-dependent manner, although nanofibers bound galectin-1 with higher affinity than galectin-3. In contrast, galectin-1 bound weakly to GlcNAc-Q11 nanofibers, while no galectin-3 binding to these nanofibers was observed. Galectin-1 binding to LacNAc-Q11 nanofibers was specific because it could be inhibited by excess soluble β-lactose, a galectin-binding carbohydrate. LacNAc-Q11 nanofibers inhibited galectin-1-mediated apoptosis of Jurkat T cells in a LacNAc concentration-dependent manner, but were unable to inhibit galectin-3 activity, consistent with galectin-binding affinity of the nanofibers. We envision that glycopeptide nanofibers capable of modulating galectin-1 bioactivity will be broadly useful as biomaterials for various medical applications, including cancer therapeutics, immunotherapy, tissue regeneration, and viral prophylaxis.

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.

Gradated assembly of multiple proteins into supramolecular nanomaterials

Biomaterials exhibiting precise ratios of different bioactive protein components are critical for applications ranging from vaccines to regenerative medicine, but their design is often hindered by limited choices and cross-reactivity of protein conjugation chemistries. Here, we describe a strategy for inducing multiple different expressed proteins of choice to assemble into nanofibres and gels with exceptional compositional control. The strategy employs 'βTail' tags, which allow for good protein expression in bacteriological cultures, yet can be induced to co-assemble into nanomaterials when mixed with additional β-sheet fibrillizing peptides. Multiple different βTail fusion proteins could be inserted into peptide nanofibres alone or in combination at predictable, smoothly gradated concentrations, providing a simple yet versatile route to install precise combinations of proteins into nanomaterials. The technology is illustrated by achieving precisely targeted hues using mixtures of fluorescent proteins, by creating nanofibres bearing enzymatic activity, and by adjusting antigenic dominance in vaccines.

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.

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.

A self-adjuvanting supramolecular vaccine carrying a folded protein antigen

This work illustrates a strategy for the design of molecularly defined immunotherapies, using a blend of supramolecular peptide self-assembly and active site-directed protein capture.

Tangled Up in Nanofibers

Self-assembled peptide nanofibers are capable of manipulating viruses.

Inspired by Porcupines

Porcupine quills inspire new design concepts for hypodermic needles.

Controllably degradable β-sheet nanofibers and gels from self-assembling depsipeptides

Self-assembled peptide materials have received considerable interest for a range of applications, including 3D cell culture, tissue engineering, and the delivery of cells and drugs. One challenge in applying such materials within these areas has been the extreme stability of β-sheet fibrillized peptides, which are resistant to proteolysis, degradation, and turnover in biological environments. In this study, we designed self-assembling depsipeptides containing ester bonds within the peptide backbone. Beta-sheet fibrillized nanofibers were formed in physiologic conditions, and two of these nanofiber-forming depsipeptides produced hydrogels that degraded controllably over the course of days-to-weeks via ester hydrolysis. With HPLC, TEM, and oscillating rheometry, we show that the rate of hydrolysis can be controlled in a straightforward manner by specifying the amino acid residues surrounding the ester bond. In 3D cell cultures, depsipeptide gels softened over the course of several days and permitted considerably more proliferation and spreading of C3H10T1/2 pluripotent stem cells than non-degradable analogs. This approach now provides a reliable and reproducible means to soften or clear β-sheet fibrillized peptide materials from biological environments.

Driving a Wedge into Acute Allergic Responses

A new strategy for stripping immunoglobulin E from mast cells has potential as a therapy for anaphylaxis-inducing allergic reactions.