Prolonged Codelivery of Hemagglutinin and a TLR7/8 Agonist in a Supramolecular Polymer-Nanoparticle Hydrogel Enhances Potency and Breadth of Influenza Vaccination

A thiol-ene click-based strategy to customize injectable polymer-nanoparticle hydrogel properties for therapeutic delivery

Polymer-nanoparticle (PNP) hydrogels are a promising injectable biomaterial platform that has been used for a wide range of biomedical applications including adhesion prevention, adoptive cell delivery, and controlled drug release. By tuning the chemical, mechanical, and erosion properties of injected hydrogel depots, additional control over cell compatibility and pharmaceutical release kinetics may be realized. Here, we employ thiol-ene click chemistry to prepare a library of modified hydroxypropylmethylcellulose (HPMC) derivatives for subsequent use in PNP hydrogel applications. When combined with poly(ethylene glycol)-b-poly(lactic acid) nanoparticles, we demonstrate that systematically altering the hydrophobic, steric, or pi stacking character of HPMC modifications can readily tailor the mechanical properties of PNP hydrogels. Additionally, we highlight the compatibility of the synthetic platform for the incorporation of cysteine-bearing peptides to access PNP hydrogels with improved bioactivity. Finally, through leveraging the tunable physical properties afforded by this method, we show hydrogel retention time in vivo can be dramatically altered without sacrificing mesh size or cargo diffusion rates. This work offers a route to optimize PNP hydrogels for a variety of translational applications and holds promise in the highly tunable delivery of pharmaceuticals and adoptive cells.

A TLR7 Agonist Conjugated to a Nanofibrous Peptide Hydrogel as a Potent Vaccine Adjuvant

Toll-like receptors (TLRs) recognize pathogen- and damage-associated molecular patterns and, in turn, trigger the release of cytokines and other immunostimulatory molecules. As a result, TLR agonists are increasingly being investigated as vaccine adjuvants. Many of these agonists are small molecules that quickly diffuse away from the vaccination site, limiting their co-localization with antigens and, thus, their effect. Here, the small-molecule TLR7 agonist 1V209 is conjugated to a positively-charged multidomain peptide (MDP) hydrogel, K2, which was previously shown to act as an adjuvant promoting humoral immunity. Mixing the 1V209-conjugated K2 50:50 with the unfunctionalized K2 produces hydrogels that retain the shear-thinning and self-healing physical properties of the original MDP while improving the solubility of 1V209 more than 200-fold compared to the unconjugated molecule. When co-delivered with ovalbumin as a model antigen, 1V209-functionalized K2 produces a robust Th2 immune response and an antigen-specific Th1 immune response superior to alum, a widely used vaccine adjuvant. Together, these results suggest that K2 MDP hydrogels functionalized with 1V209 are a promising adjuvant for vaccines against infectious diseases, especially those benefiting from a combined Th1 and Th2 immune response.

Amphiphilic pH-responsive core-shell nanoparticles can increase the performances of cellulose-based drug delivery systems

Polymer and nanoparticles (NPs) together are able to form nanocomposite materials that combine the beneficial properties of the traditional single systems. In this work, we propose a stimuli-responsive nanocomposite system which combines pH-responsive NPs with cellulose. Ring opening polymerization (ROP) followed by two reversible addition-fragmentation chain transfer (RAFT) polymerization steps were performed to synthetize ((PHEMA-graft-LA12)-co-PMAA)-b-PDEGMA copolymer characterized by tailored molecular weights and low polydispersity values. Uniform NPs were obtained by nanoprecipitation of the so-obtained copolymer in water. Moreover, drug release studies (using rhodamine b, fluorescein isothiocyanate, pyrene and 5-fluorouracil) at different pHs demonstrated the pH-responsivity of NPs, revealing a significant improvement of hydrophobic molecules release at acidic conditions. In vitro tests verified the biocompatibility of NPs and the efficacy in decreasing cancer cell viability. Finally, NPs were loaded into hydroxypropylmethyl-cellulose-C12 matrix to obtain the final polymer-NPs composite system. The composite systems showed the ability to sustain the release of low steric hindrance drugs loaded with NPs and high steric hindrance ones loaded within the polymeric network. Overall, the proposed pH-responsive drug delivery system represents a co-delivery device which could be applied for localized treatment in different combined therapeutic program.

Self-Adjuvanting Adenoviral Nanovaccine for Effective T-Cell-Mediated Immunity and Long-Lasting Memory Cell Activation against Tuberculosis

An enhanced vaccine is immediately required to swap the more than 100 year-old bacillus Calmette-Guerin (BCG) vaccine against tuberculosis. Here, trimethyl chitosan-loaded inactivated Mycobacterium smegmatis (MST), along with potent adenovirus hexon protein (AdHP), and toll-like receptor (TLR)-1/2 as a nanovaccine, was developed against tuberculosis (TB). The nanoformulation increased the bioavailability of MST and elicited the targeting ability. Nanovaccines have a size range of 183.5 ± 9.5 nm with a spherical morphology and uniform distribution. The nanovaccine exhibited a higher release of antigen in acidic pH, and this is mainly due to protonation of ionizable groups in polymeric materials. The nanovaccine facilitated the effective cellular uptake of bone-marrow-derived dendritic cells and progressive endosomal escape in a shorter period. In vitro analyses indicated that the nanovaccine activated cytokine and T-cell production and also assisted in humoral immunity by producing antibodies. The nanovaccine was able to induce more cellular and humoral memory cells and a better protective immune response. Nanomaterials effectively delivered the MST, AdHP, and TLR1/2 antigens to the major histocompatibility complex class I and II pathways to generate protective cytotoxic CD8+ and CD4+ T-cells. In vivo experiments, compared with free MST and BCG, showed that mice immunized with the nanovaccine induced more specific CD4+, CD8+, and memory T-cell activations. Overall, the fabricated nanovaccine was able to control the release of antigens and adjuvants and enhance memory cell activation and humoral immunity against TB.

Injectable hydrogel based on liposome self-assembly for controlled release of small hydrophilic molecules

Controlled release of low molecular weight hydrophilic drugs, administered locally, allows maintenance of high concentrations at the target site, reduces systemic side effects, and improves patient compliance. Injectable hydrogels are commonly used as a vehicle. However, slow release of low molecular weight hydrophilic drugs is very difficult to achieve, mainly due to a rapid diffusion of the drug out of the drug delivery system. Here we present an injectable and self-healing hydrogel based entirely on the self-assembly of liposomes. Gelation of liposomes, without damaging their structural integrity, was induced by modifying the cholesterol content and surface charge. The small hydrophilic molecule, sodium fluorescein, was loaded either within the extra-liposomal space or encapsulated into the aqueous cores of the liposomes. This encapsulation strategy enabled the achievement of controlled and adjustable release profiles, dependent on the mechanical strength of the gel. The hydrogel had a high mechanical strength, minimal swelling, and slow degradation. The liposome-based hydrogel had prolonged mechanical stability in vivo with benign tissue reaction. This work presents a new class of injectable hydrogel that holds promise as a versatile drug delivery system. STATEMENT OF SIGNIFICANCE: The porous nature of hydrogels poses a challenge for delivering small hydrophilic drug, often resulting in initial burst release and shorten duration of release. This issue is particularly pronounced with physically crosslinked hydrogels, since their matrix can swell and dissipate rapidly, but even in cases where the polymers in the hydrogel are covalently cross-linked, small molecules can be rapidly released through its porous mesh. Here we present an injectable self-healing hydrogel based entirely on the self-assembly of liposomes. Small hydrophilic molecules were entrapped inside the extra-liposomal space or loaded into the aqueous cores of the liposomes, allowing controlled and tunable release profiles.

Peptide-TLR7/8a-Coordinated DNA Vaccines Elicit Enhanced Immune Responses against Infectious Diseases

DNA vaccines represent an innovative approach for the immunization of diverse diseases. However, their clinical trial outcomes are constrained by suboptimal transfection efficiency and immunogenicity. In this work, we present a universal methodology involving the codelivery of Toll-like receptor 7/8 agonists (TLR7/8a) and antigen gene using TLR7/8a-conjugated peptide-coated poly(β-amino ester) (PBAE) nanoparticles (NPs) to augment delivery efficiency and immune response. Peptide-TLR7/8a-coated PBAE NPs exhibit advantageous biophysical attributes, encompassing diminutive particle dimensions, nearly neutral ζ potential, and stability in the physiological environment. This synergistic approach not only ameliorates the stability of plasmid DNA (pDNA) and gene delivery efficacy but also facilitates subsequent antigen production. Furthermore, under optimal formulation conditions, the TLR7/8a-conjugated peptide coated PBAE NPs exhibit a potent capacity to induce robust immune responses. Collectively, this nanoparticulate gene delivery system demonstrates heightened transfection efficacy, stability, biodegradability, immunostimulatory effect, and low toxicity, making it a promising platform for the clinical advancement of DNA vaccines.

Improved biodistribution and enhanced immune response of subunit vaccine using a nanostructure formed by self-assembly of ascorbyl palmitate

New adjuvant strategies are needed to improve protein-based subunit vaccine immunogenicity. We examined the potential to use nanostructure of 6-O-ascorbyl palmitate to formulate ovalbumin (OVA) protein and an oligodeoxynucleotide (CpG-ODN) (OCC). In mice immunized with a single dose, OCC elicited an OVA-specific immune response superior to OVA/CpG-ODN solution (OC). Rheological studies demonstrated OCC's self-assembling viscoelastic properties. Biodistribution studies indicated that OCC prolonged OVA and CpG-ODN retention at injection site and lymph nodes, reducing systemic spread. Flow-cytometry assays demonstrated that OCC promoted OVA and CpG-ODN co-uptake by Ly6ChiCD11bhiCD11c+ monocytes. OCC and OC induced early IFN-γ in lymph nodes, but OCC led to higher concentration. Conversely, mice immunized with OC showed higher serum IFN-γ concentration compared to those immunized with OCC. In mice immunized with OCC, NK1.1+ cells were the IFN-γ major producers, and IFN-γ was essential for OVA-specific IgG2c switching. These findings illustrate how this nanostructure improves vaccine's response.

Recent Insights into the Molecular Mechanisms of the Toll-like Receptor Response to Influenza Virus Infection

Influenza A viruses (IAVs) pose a significant global threat to human health. A tightly controlled host immune response is critical to avoid any detrimental effects of IAV infection. It is critical to investigate the association between the response of Toll-like receptors (TLRs) and influenza virus. Because TLRs may act as a double-edged sword, a balanced TLR response is critical for the overall benefit of the host. Consequently, a thorough understanding of the TLR response is essential for targeting TLRs as a novel therapeutic and prophylactic intervention. To date, a limited number of studies have assessed TLR and IAV interactions. Therefore, further research on TLR interactions in IAV infection should be conducted to determine their role in host-virus interactions in disease causation or clearance of the virus. Although influenza virus vaccines are available, they have limited efficacy, which should be enhanced to improve their efficacy. In this study, we discuss the current status of our understanding of the TLR response in IAV infection and the strategies adopted by IAVs to avoid TLR-mediated immune surveillance, which may help in devising new therapeutic or preventive strategies. Furthermore, recent advances in the use of TLR agonists as vaccine adjuvants to enhance influenza vaccine efficacy are discussed.

Biomaterial engineering strategies for B cell immunity modulations

B cell immunity has a penetrating effect on human health and diseases. Therapeutics aiming to modulate B cell immunity have achieved remarkable success in combating infections, autoimmunity, and malignancies. However, current treatments still face significant limitations in generating effective long-lasting therapeutic B cell responses for many conditions. As the understanding of B cell biology has deepened in recent years, clearer regulation networks for B cell differentiation and antibody production have emerged, presenting opportunities to overcome current difficulties and realize the full therapeutic potential of B cell immunity. Biomaterial platforms have been developed to leverage these emerging concepts to augment therapeutic humoral immunity by facilitating immunogenic reagent trafficking, regulating T cell responses, and modulating the immune microenvironment. Moreover, biomaterial engineering tools have also advanced our understanding of B cell biology, further expediting the development of novel therapeutics. In this review, we will introduce the general concept of B cell immunobiology and highlight key biomaterial engineering strategies in the areas including B cell targeted antigen delivery, sustained B cell antigen delivery, antigen engineering, T cell help optimization, and B cell suppression. We will also discuss our perspective on future biomaterial engineering opportunities to leverage humoral immunity for therapeutics.

Lymphatic distribution considerations for subunit vaccine design and development

Subunit vaccines are an important platform for controlling current and emerging infectious diseases. The lymph nodes are the primary site generating the humoral response and delivery of antigens to these sites is critical to effective immunization. Indeed, the duration of antigen exposure within the lymph node is correlated with the antibody response. While current licensed vaccines are typically given through the intramuscular route, injecting vaccines subcutaneously allows for direct access to lymphatic vessels and therefore can enhance the transfer of antigen to the lymph nodes. However, protein subunit antigen uptake into the lymph nodes is inefficient, and subunit vaccines require adjuvants to stimulate the initial immune response. Therefore, formulation strategies have been developed to enhance the exposure of subunit proteins and adjuvants to the lymph nodes by increasing lymphatic uptake or prolonging the retention at the injection site. Given that lymph node exposure is a crucial consideration in vaccine design, in depth analyses of the pharmacokinetics of antigens and adjuvants should be the focus of future preclinical and clinical studies. This review will provide an overview of formulation strategies for targeting the lymphatics and prolonging antigen exposure and will discuss pharmacokinetic evaluations which can be applied toward vaccine development.

A TLR7 Agonist Conjugated to a Nanofibrous Peptide Hydrogel as a Potent Vaccine Adjuvant

Toll-like receptors (TLRs) recognize pathogen- and damage-associated molecular patterns and, in turn, trigger the release of cytokines and other immunostimulatory molecules. As a result, TLR agonists are increasingly being investigated as vaccine adjuvants, though many of these agonists are small molecules that quickly diffuse away from the vaccination site, limiting their co-localization with antigens and, thus, their effect. Here, the small-molecule TLR7 agonist 1V209 is conjugated to a positively-charged multidomain peptide (MDP) hydrogel, K 2 , which was previously shown to act as an adjuvant promoting humoral immunity. Mixing the 1V209-conjugated K 2 50:50 with the unfunctionalized K 2 produces hydrogels that retain the shear-thinning and self-healing physical properties of the original MDP, while improving the solubility of 1V209 more than 200-fold compared to the unconjugated molecule. When co-delivered with ovalbumin as a model antigen, 1V209-functionalized K 2 produces antigen-specific IgG titers that were statistically similar to alum, the gold standard adjuvant, and a significantly lower ratio of Th2-associated IgG1 to Th1-associated IgG2a than alum, suggesting a more balanced Th1 and Th2 response. Together, these results suggest that K 2 MDP hydrogels functionalized with 1V209 are a promising adjuvant for vaccines against infectious diseases, especially those benefiting from a combined Th1 and Th2 immune response.

Table of Contents

Activation of toll-like receptors (TLRs) stimulates a signaling cascade to induce an immune response. A TLR7 agonist was conjugated to an injectable peptide hydrogel, which was then used to deliver a model vaccine antigen. This platform produced antibody titers similar to the gold standard adjuvant alum and demonstrated an improved balance between Th1- and Th2-mediated immunity over alum.

Nanoparticle-Conjugated Toll-Like Receptor 9 Agonists Improve the Potency, Durability, and Breadth of COVID-19 Vaccines

Development of effective vaccines for infectious diseases has been one of the most successful global health interventions in history. Though, while ideal subunit vaccines strongly rely on antigen and adjuvant(s) selection, the mode and time scale of exposure to the immune system has often been overlooked. Unfortunately, poor control over the delivery of many adjuvants, which play a key role in enhancing the quality and potency of immune responses, can limit their efficacy and cause off-target toxicities. There is a critical need for improved adjuvant delivery technologies to enhance their efficacy and boost vaccine performance. Nanoparticles have been shown to be ideal carriers for improving antigen delivery due to their shape and size, which mimic viral structures but have been generally less explored for adjuvant delivery. Here, we describe the design of self-assembled poly(ethylene glycol)-b-poly(lactic acid) nanoparticles decorated with CpG, a potent TLR9 agonist, to increase adjuvanticity in COVID-19 vaccines. By controlling the surface density of CpG, we show that intermediate valency is a key factor for TLR9 activation of immune cells. When delivered with the SARS-CoV-2 spike protein, CpG nanoparticle (CpG-NP) adjuvant greatly improves the magnitude and duration of antibody responses when compared to soluble CpG, and results in overall greater breadth of immunity against variants of concern. Moreover, encapsulation of CpG-NP into injectable polymeric-nanoparticle (PNP) hydrogels enhances the spatiotemporal control over codelivery of CpG-NP adjuvant and spike protein antigen such that a single immunization of hydrogel-based vaccines generates humoral responses comparable to those of a typical prime-boost regimen of soluble vaccines. These delivery technologies can potentially reduce the costs and burden of clinical vaccination, both of which are key elements in fighting a pandemic.

Nanoparticles and Antiviral Vaccines

Viruses have threatened human lives for decades, causing both chronic and acute infections accompanied by mild to severe symptoms. During the long journey of confrontation, humans have developed intricate immune systems to combat viral infections. In parallel, vaccines are invented and administrated to induce strong protective immunity while generating few adverse effects. With advancements in biochemistry and biophysics, different kinds of vaccines in versatile forms have been utilized to prevent virus infections, although the safety and effectiveness of these vaccines are diverse from each other. In this review, we first listed and described major pathogenic viruses and their pandemics that emerged in the past two centuries. Furthermore, we summarized the distinctive characteristics of different antiviral vaccines and adjuvants. Subsequently, in the main body, we reviewed recent advances of nanoparticles in the development of next-generation vaccines against influenza viruses, coronaviruses, HIV, hepatitis viruses, and many others. Specifically, we described applications of self-assembling protein polymers, virus-like particles, nano-carriers, and nano-adjuvants in antiviral vaccines. We also discussed the therapeutic potential of nanoparticles in developing safe and effective mucosal vaccines. Nanoparticle techniques could be promising platforms for developing broad-spectrum, preventive, or therapeutic antiviral vaccines.

Use of a biomimetic hydrogel depot technology for sustained delivery of GLP-1 receptor agonists reduces burden of diabetes management

Glucagon-like peptide-1 (GLP-1) is an incretin hormone and neurotransmitter secreted from intestinal L cells in response to nutrients to stimulate insulin and block glucagon secretion in a glucose-dependent manner. Long-acting GLP-1 receptor agonists (GLP-1 RAs) have become central to treating type 2 diabetes (T2D); however, these therapies are burdensome, as they must be taken daily or weekly. Technological innovations that enable less frequent administrations would reduce patient burden and increase patient compliance. Herein, we leverage an injectable hydrogel depot technology to develop a GLP-1 RA drug product capable of months-long GLP-1 RA delivery. Using a rat model of T2D, we confirm that one injection of hydrogel-based therapy sustains exposure of GLP-1 RA over 42 days, corresponding to a once-every-4-months therapy in humans. Hydrogel therapy maintains management of blood glucose and weight comparable to daily injections of a leading GLP-1 RA drug. This long-acting GLP-1 RA treatment is a promising therapy for more effective T2D management.

Broad and Durable Humoral Responses Following Single Hydrogel Immunization of SARS-CoV-2 Subunit Vaccine

Most vaccines require several immunizations to induce robust immunity, and indeed, most SARS-CoV-2 vaccines require an initial two-shot regimen followed by several boosters to maintain efficacy. Such a complex series of immunizations unfortunately increases the cost and complexity of populations-scale vaccination and reduces overall compliance and vaccination rate. In a rapidly evolving pandemic affected by the spread of immune-escaping variants, there is an urgent need to develop vaccines capable of providing robust and durable immunity. In this work, a single immunization SARS-CoV-2 subunit vaccine is developed that can rapidly generate potent, broad, and durable humoral immunity. Injectable polymer-nanoparticle (PNP) hydrogels are leveraged as a depot technology for the sustained delivery of a nanoparticle antigen (RND-NP) displaying multiple copies of the SARS-CoV-2 receptor-binding domain (RBD) and potent adjuvants including CpG and 3M-052. Compared to a clinically relevant prime-boost regimen with soluble vaccines formulated with CpG/alum or 3M-052/alum adjuvants, PNP hydrogel vaccines more rapidly generated higher, broader, and more durable antibody responses. Additionally, these single-immunization hydrogel-based vaccines elicit potent and consistent neutralizing responses. Overall, it is shown that PNP hydrogels elicit improved anti-COVID immune responses with only a single administration, demonstrating their potential as critical technologies to enhance overall pandemic readiness.

Prolonging the delivery of influenza virus vaccine improves the quantity and quality of the induced immune responses in mice

Introduction

Influenza vaccines play a vital role in protecting individuals from influenza virus infection and severe illness. However, current influenza vaccines have suboptimal efficacy, which is further reduced in cases where the vaccine strains do not match the circulating strains. One strategy to enhance the efficacy of influenza vaccines is by extended antigen delivery, thereby mimicking the antigen kinetics of a natural infection. Prolonging antigen availability was shown to quantitatively enhance influenza virus-specific immune responses but how it affects the quality of the induced immune response is unknown. Therefore, the current study aimed to investigate whether prolongation of the delivery of influenza vaccine improves the quality of the induced immune responses over that induced by prime-boost immunization.

Methods

Mice were given daily doses of whole inactivated influenza virus vaccine for periods of 14, 21, or 28 days; the control group received prime-boost immunization with a 28 days interval.

Results

Our data show that the highest levels of cellular and humoral immune responses were induced by 28 days of extended antigen delivery, followed by 21, and 14 days of delivery, and prime-boost immunization. Moreover, prolonging vaccine delivery also improved the quality of the induced antibody response, as indicated by higher level of high avidity antibodies, a balanced IgG subclass profile, and a higher level of cross-reactive antibodies.

Conclusions

Our findings contribute to a better understanding of the immune response to influenza vaccination and have important implications for the design and development of future slow-release influenza vaccines.

Optimization of an alum-anchored clinical HIV vaccine candidate

In the ongoing effort to develop a vaccine against HIV, vaccine approaches that promote strong germinal center (GC) responses may be critical to enable the selection and affinity maturation of rare B cell clones capable of evolving to produce broadly neutralizing antibodies. We previously demonstrated an approach for enhancing GC responses and overall humoral immunity elicited by alum-adjuvanted protein immunization via the use of phosphoserine (pSer) peptide-tagged immunogens that stably anchor to alum particles via ligand exchange with the alum particle surface. Here, using a clinically relevant stabilized HIV Env trimer termed MD39, we systematically evaluated the impact of several parameters relevant to pSer tag composition and trimer immunogen design to optimize this approach, including phosphate valency, amino acid sequence of the trimer C-terminus used for pSer tag conjugation, and structure of the pSer tag. We also tested the impact of co-administering a potent saponin/monophosphoryl lipid A (MPLA) nanoparticle co-adjuvant with alum-bound trimers. We identified MD39 trimer sequences bearing an optimized positively-charged C-terminal amino acid sequence, which, when conjugated to a pSer tag with four phosphates and a polypeptide spacer, bound very tightly to alum particles while retaining a native Env-like antigenicity profile. This optimized pSer-trimer design elicited robust antigen-specific GC B cell and serum IgG responses in mice. Through this optimization, we present a favorable MD39-pSer immunogen construct for clinical translation.

An Analysis of Linker-Dependent Effects on the APC Activation and In Vivo Immunogenicity of an R848-Conjugated Influenza Vaccine

Subunit or inactivated vaccines comprise the majority of vaccines used against viral and bacterial pathogens. However, compared to their live/attenuated counterparts, these vaccines often demonstrate reduced immunogenicity, requiring multiple boosters and or adjuvants to elicit protective immune responses. For this reason, studies of adjuvants and the mechanism through which they can improve inactivated vaccine responses are critical for the development of vaccines with increased efficacy. Studies have shown that the direct conjugation of adjuvant to antigen promotes vaccine immunogenicity, with the advantage of both the adjuvant and antigen targeting the same cell. Using this strategy of direct linkage, we developed an inactivated influenza A (IAV) vaccine that is directly conjugated with the Toll-like receptor 7/8 agonist resiquimod (R848) through a heterobifunctional crosslinker. Previously, we showed that this vaccine resulted in improved protection and viral clearance in newborn nonhuman primates compared to a non-adjuvanted vaccine. We subsequently discovered that the choice of linker used to conjugate R848 to the virus alters the stimulatory activity of the vaccine, promoting increased maturation and proinflammatory cytokine production from DC differentiated in vitro. With this knowledge, we explored how the choice of crosslinker impacts the stimulatory activity of these vaccines. We found that the linker choice alters signaling through the NF-κB pathway in human monocyte-derived dendritic cells (moDCs). Further, we extended our analyses to in vivo differentiated APC present in human peripheral blood, replicating the linker-dependent differences found in in vitro differentiated cells. Finally, we demonstrated in a mouse model that the choice of linker impacts the amount of IAV-specific IgG antibody produced in response to vaccination. These data enhance our understanding of conjugation approaches for improving vaccine immunogenicity.

Vaccine adjuvants: mechanisms and platforms

Adjuvants are indispensable components of vaccines. Despite being widely used in vaccines, their action mechanisms are not yet clear. With a greater understanding of the mechanisms by which the innate immune response controls the antigen-specific response, the adjuvants' action mechanisms are beginning to be elucidated. Adjuvants can be categorized as immunostimulants and delivery systems. Immunostimulants are danger signal molecules that lead to the maturation and activation of antigen-presenting cells (APCs) by targeting Toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) to promote the production of antigen signals and co-stimulatory signals, which in turn enhance the adaptive immune responses. On the other hand, delivery systems are carrier materials that facilitate antigen presentation by prolonging the bioavailability of the loaded antigens, as well as targeting antigens to lymph nodes or APCs. The adjuvants' action mechanisms are systematically summarized at the beginning of this review. This is followed by an introduction of the mechanisms, properties, and progress of classical vaccine adjuvants. Furthermore, since some of the adjuvants under investigation exhibit greater immune activation potency than classical adjuvants, which could compensate for the deficiencies of classical adjuvants, a summary of the adjuvant platforms under investigation is subsequently presented. Notably, we highlight the different action mechanisms and immunological properties of these adjuvant platforms, which will provide a wide range of options for the rational design of different vaccines. On this basis, this review points out the development prospects of vaccine adjuvants and the problems that should be paid attention to in the future.

Nanostructures for prevention, diagnosis, and treatment of viral respiratory infections: from influenza virus to SARS-CoV-2 variants

Viruses are a major cause of mortality and socio-economic downfall despite the plethora of biopharmaceuticals designed for their eradication. Conventional antiviral therapies are often ineffective. Live-attenuated vaccines can pose a safety risk due to the possibility of pathogen reversion, whereas inactivated viral vaccines and subunit vaccines do not generate robust and sustained immune responses. Recent studies have demonstrated the potential of strategies that combine nanotechnology concepts with the diagnosis, prevention, and treatment of viral infectious diseases. The present review provides a comprehensive introduction to the different strains of viruses involved in respiratory diseases and presents an overview of recent advances in the diagnosis and treatment of viral infections based on nanotechnology concepts and applications. Discussions in diagnostic/therapeutic nanotechnology-based approaches will be focused on H1N1 influenza, respiratory syncytial virus, human parainfluenza virus type 3 infections, as well as COVID-19 infections caused by the SARS-CoV-2 virus Delta variant and new emerging Omicron variant.

Long-acting vaccine delivery systems

Bolus vaccines are often administered multiple times due to rapid clearance and reduced transportation to draining lymph nodes resulting in inadequate activation of T and B lymphocytes. In order to achieve adaptive immunity, prolonged exposure of antigens to these immune cells is crucial. Recent research has been focusing on developing long-acting biomaterial-based vaccine delivery systems, which can modulate the release of encapsulated antigens or epitopes to facilitate enhanced antigen presentation in lymph nodes and subsequently achieve robust T and B cell responses. Over the past few years, various polymers and lipids have been extensively explored to develop effective biomaterial-based vaccine strategies. The article reviews relevant polymer and lipid-based strategies used to prepare long-acting vaccine carriers and discusses their results concerning immune responses.

Subcutaneous delivery of an antibody against SARS-CoV-2 from a supramolecular hydrogel depot

Prolonged maintenance of therapeutically-relevant levels of broadly neutralizing antibodies (bnAbs) is necessary to enable passive immunization against infectious disease. Unfortunately, protection only lasts for as long as these bnAbs remain present at a sufficiently high concentration in the body. Poor pharmacokinetics and burdensome administration are two challenges that need to be addressed in order to make pre- and post-exposure prophylaxis with bnAbs feasible and effective. In this work, we develop a supramolecular hydrogel as an injectable, subcutaneous depot to encapsulate and deliver antibody drug cargo. This polymer-nanoparticle (PNP) hydrogel exhibits shear-thinning and self-healing properties that are required for an injectable drug delivery vehicle. In vitro drug release assays and diffusion measurements indicate that the PNP hydrogels prevent burst release and slow the release of encapsulated antibodies. Delivery of bnAbs against SARS-CoV-2 from PNP hydrogels is compared to standard routes of administration in a preclinical mouse model. We develop a multi-compartment model to understand the ability of these subcutaneous depot materials to modulate the pharmacokinetics of released antibodies; the model is extrapolated to explore the requirements needed for novel materials to successfully deliver relevant antibody therapeutics with different pharmacokinetic characteristics.

Sustained Delivery of GLP-1 Receptor Agonists from Injectable Biomimetic Hydrogels Improves Treatment of Diabetes

Glucagon-like peptide-1 (GLP-1) is an incretin hormone and neurotransmitter secreted from intestinal L-cells in response to nutrients to stimulate insulin and block glucagon secretion in a glucose-dependent manner. GLP-1 in itself is rapidly degraded, but long-acting GLP-1 receptor agonists (GLP-1 RAs) have become central in the treatment of T2D because of the beneficial effects extending also beyond glucose control. Currently, these therapeutics must be injected either daily or weekly or taken daily orally, leaving room for technological innovations that enable less frequent administrations, which will reduce patient burden and increase patient compliance. An ideal GLP-1 RA drug product would provide continuous therapy for upwards of four months from a single administration to match the cadence with which T2D patients typically visit their physician. In this work, we leveraged an injectable hydrogel depot technology to develop a long-acting GLP-1 RA drug product. By modulating the hydrogel properties to tune GLP-1 RA retention within the hydrogel depot, we engineered formulations capable of months-long GLP-1 RA delivery. Using a rat model of T2D, we confirmed that a single injection of hydrogel-based therapies exhibits sustained exposure of GLP-1 RA over 42 days, corresponding to a once-every four month therapy in humans. Moreover, these hydrogel therapies maintained optimal management of blood glucose and weight comparable to daily injections of a leading GLP-1 RA drug molecule. The pharmacokinetics and pharmacodynamics of these hydrogel-based long-acting GLP-1 RA treatments are promising for development of novel therapies reducing treatment burden for more effective management of T2D.

Dynamic Imine Bonding Facilitates Mannan Release from a Nanofibrous Peptide Hydrogel

Recently, there has been increased interest in using mannan as an immunomodulatory bioconjugate. Despite notable immunological and functional differences between the reduced (R-Man) and oxidized (O-Man) forms of mannan, little is known about the impact of mannan oxidation state on its in vivo persistence or its potential controlled release from biomaterials that may improve immunotherapeutic or prophylactic efficacy. Here, we investigate the impact of oxidation state on the in vitro and in vivo release of mannan from a biocompatible and immunostimulatory multidomain peptide hydrogel, K2(SL)6K2 (abbreviated as K2), that has been previously used for the controlled release of protein and small molecule payloads. We observed that O-Man released more slowly from K2 hydrogels in vitro than R-Man. In vivo, the clearance of O-Man from K2 hydrogels was slower than O-Man alone. We attributed the slower release rate to the formation of dynamic imine bonds between reactive aldehyde groups on O-Man and the lysine residues on K2. This imine interaction was also observed to improve K2 + O-Man hydrogel strength and shear recovery without significantly influencing secondary structure or peptide nanofiber formation. There were no observed differences in the in vivo release rates of O-Man loaded in K2, R-Man loaded in K2, and R-Man alone. These data suggest that, after subcutaneous injection, R-Man naturally persists longer in vivo than O-Man and minimally interacts with the peptide hydrogel. These results highlight a potentially critical, but previously unreported, difference in the in vivo behavior of O-Man and R-Man and demonstrate that K2 can be used to normalize the release of O-Man to that of R-Man. Further, since K2 itself is an adjuvant, a combination of O-Man and K2 could be used to enhance the immunostimulatory effects of O-Man for applications such as infectious disease vaccines and cancer immunotherapy.

Immunoprotection Efficacy of Con A-Purified Proteins against Haemonchus contortus in Goats

Parasitic nematodes are important pathogens that infect animals, causing significant economic losses globally. Current repeated treatments have led to widespread anthelmintic resistance in nematode populations, so vaccine development offers an alternative control approach. However, only one effective vaccine (named Barbervax) has been developed to protect animals against one of the most pathogenic nematodes of ruminants—Haemonchus contortus (the barber’s pole worm). This vaccine contains a dominant component, Concanavalin A (Con A) purified H11 antigen, which has been shown to induce high levels (>85%) of immune protection in sheep breeds, but in goat breeds, the immunoprotection test of this native protein is still lacking. Here, we evaluated the protective efficacy of low-dose Con A-purified proteins for controlling the H. contortus infection in goats. Four-month-old Boer goats were equally divided into two vaccinated groups of 5 μg and 10 μg native proteins, and one adjuvant control. Each goat was immunized subcutaneously thrice and then challenged with 7000 infective third-stage larvae (L3s). The fecal egg count (FEC), degree of anemia, antibody levels of serum and abomasum mucosa, as well as worm burdens, were detected in experimental goats. Our results showed that both 5 μg and 10 μg vaccinated groups induced the effective protection in goats, reduced mean FEC by 71.8% and 68.6%, and mean worm burdens by 69.8% and 61.6%, respectively, compared to the adjuvant control. In addition, we detected that the serum antibody responses to the Con A-purified proteins were dominated by the IgG subtype, but the mucosal antibody responses were not detected. These data demonstrate Con A-purified proteins induced effective immunoprotection in goats, and underline their significance for controlling this widespread parasite.

Toll-like receptor (TLR) agonists as a driving force behind next-generation vaccine adjuvants and cancer therapeutics

Until recently, the development of new human adjuvants was held back by a poor understanding of their mechanisms of action. The field was revolutionized by the discovery of the toll-like receptors (TLRs), innate immune receptors that directly or indirectly are responsible for detecting pathogen-associated molecular patterns (PAMPs) and respond to them by activating innate and adaptive immune pathways. Hundreds of ligands targeting various TLRs have since been identified and characterized as vaccine adjuvants. This work has important implications not only for the development of vaccines against infectious diseases but also for immuno-therapies against cancer, allergy, Alzheimer's disease, drug addiction and other diseases. Each TLR has its own specific tissue localization and downstream gene signalling pathways, providing researchers the opportunity to precisely tailor adjuvants with specific immune effects. TLR agonists can be combined with other TLR or alternative adjuvants to create combination adjuvants with synergistic or modulatory effects. This review provides an introduction to the various classes of TLR adjuvants and their respective signalling pathways. It provides an overview of recent advancements in the TLR field in the past 2-3 years and discusses criteria for selecting specific TLR adjuvants based on considerations, such as disease mechanisms and correlates of protection, TLR immune biasing capabilities, route of administration, antigen compatibility, new vaccine technology platforms, and age- and species-specific effects.

Sustained delivery approaches to improving adaptive immune responses

The immune system is one of the most important, complex biological networks regulating and protecting human health. Its precise modulation can prevent deadly infections and fight cancer. Accordingly, prophylactic vaccines and cancer immunotherapies are some of the most powerful technologies to protect against potential dangers through training of the immune system. Upon immunization, activation and maturation of B and T cells of the adaptive immune system are necessary for development of proper humoral and cellular protection. Yet, the exquisite organization of the immune system requires spatiotemporal control over the exposure of immunomodulatory signals. For example, while the human immune system has evolved to develop immunity to natural pathogenic infections that often last for weeks, current prophylactic vaccination technologies only expose the immune system to immunomodulatory signals for hours to days. It has become clear that leveraging sustained release technologies to prolong immunogen and adjuvant exposure can increase the potency, durability, and quality of adaptive immune responses. Over the past several years, tremendous breakthroughs have been made in the design of novel biomaterials such as nanoparticles, microparticles, hydrogels, and microneedles that can precisely control and the presentation of immunomodulatory signals to the immune system. In this review, we discuss relevant sustained release strategies and their corresponding benefits to cellular and humoral responses.

Use of Nanomaterials for Diagnosis and Treatment: The Advancement of Next-Generation Antiviral Therapy

Globally, viral illness propagation is the leading cause of morbidity and death, causing wreaking havoc on socioeconomic development and health care systems. The rise of infected individuals has outpaced the existing critical care facilities. Early and sophisticated methods are desperately required in this respect to halt the spread of the infection. Therefore, early detection of infectious agents and an early treatment approach may help minimize viral outbreaks. Conventional point-of-care diagnostic techniques such as computed tomography scan, quantitative real time polymerase chain reaction (qRT-PCR), X-ray, and immunoassay are still deemed valuable. However, the labor demanding, low sensitivity, and complex infrastructure needed for these methods preclude their use in distant areas. Nanotechnology has emerged as a potentially transformative technology due to its promise as an effective theranostic platform for diagnosing and treating viral infection, circumventing the limits of traditional techniques. Their unique physical and chemical characteristics make nanoparticles (NPs) advantageous for drug delivery platforms due to their size, encapsulation efficiency, improved bioavailability, effectiveness, immunogenicity, and antiviral response. This study discusses the recent research on nanotechnology-based treatments designed to combat new viruses.

Subcutaneous delivery of an antibody against SARS-CoV-2 from a supramolecular hydrogel depot

Prolonged maintenance of therapeutically-relevant levels of broadly neutralizing antibodies (bnAbs) is necessary to enable passive immunization against infectious disease. Unfortunately, protection only lasts for as long as these bnAbs remain present at a sufficiently high concentration in the body. Poor pharmacokinetics and burdensome administration are two challenges that need to be addressed in order to make pre- and post-exposure prophylaxis with bnAbs feasible and effective. In this work, we develop a supramolecular hydrogel as an injectable, subcutaneous depot to encapsulate and deliver antibody drug cargo. This polymer-nanoparticle (PNP) hydrogel exhibits shear-thinning and self-healing properties that are required for an injectable drug delivery vehicle. In vitro drug release assays and diffusion measurements indicate that the PNP hydrogels prevent burst release and slow the release of encapsulated antibodies. Delivery of bnAbs against SARS-CoV-2 from PNP hydrogels is compared to standard routes of administration in a preclinical mouse model. We develop a multi-compartment model to understand the ability of these subcutaneous depot materials to modulate the pharmacokinetics of released antibodies; the model is extrapolated to explore the requirements needed for novel materials to successfully deliver relevant antibody therapeutics with different pharmacokinetic characteristics.

Special Features of Polyester-Based Materials for Medical Applications

This article presents current possibilities of using polyester-based materials in hard and soft tissue engineering, wound dressings, surgical implants, vascular reconstructive surgery, ophthalmology, and other medical applications. The review summarizes the recent literature on the key features of processing methods and potential suitable combinations of polyester-based materials with improved physicochemical and biological properties that meet the specific requirements for selected medical fields. The polyester materials used in multiresistant infection prevention, including during the COVID-19 pandemic, as well as aspects covering environmental concerns, current risks and limitations, and potential future directions are also addressed. Depending on the different features of polyester types, as well as their specific medical applications, it can be generally estimated that 25-50% polyesters are used in the medical field, while an increase of at least 20% has been achieved since the COVID-19 pandemic started. The remaining percentage is provided by other types of natural or synthetic polymers; i.e., 25% polyolefins in personal protection equipment (PPE).

Immune Enhancement by the Tetra-Peptide Hydrogel as a Promising Adjuvant for an H7N9 Vaccine against Highly Pathogenic H7N9 Virus

Background: Short peptide hydrogel was reported as a possible adjuvant for vaccines. In order to evaluate whether the Tetra-Peptide Hydrogel can be a promising adjuvant for an H7N9 vaccine against the highly pathogenic H7N9 virus, we conducted this study. Methods: Tetra-Peptide Hydrogels (D and L conformations) were prepared by a self-assembly system using a Naproxen acid modified tetra peptide of GFFY (Npx-GFFY). Mice received two immunizations with the D-Tetra-Peptide Hydrogel adjuvant vaccine, the L-Tetra-Peptide Hydrogel adjuvant vaccine, or the split vaccine. Fourteen days following the second dose, the mice were challenged with the highly pathogenic A/Guangdong/GZ8H002/2017(H7N9) virus. The mice were observed for signs of illness, weight loss, pathological alterations of the lung tissues and immune responses in the following 2 weeks. Results: The D/L-Tetra-Peptide Hydrogels resembled long bars with hinges on each other, with a diameter of ~10 nm. The H7N9 vaccine was observed to adhere to the hydrogel. All the unvaccinated mice were dead by 8 days post infection with H7N9. The mice immunized by the split H7N9 vaccine were protected against infection with H7N9. Mice immunized by D/L-Tetra-Peptide Hydrogel adjuvant vaccines experienced shorter symptomatic periods and their micro-neutralization titers were higher than in the split H7N9 vaccine at 2 weeks post infection. The hemagglutinating inhibition (HI) titer in the L-Tetra-Peptide Hydrogel adjuvant vaccine group was higher than that in the split H7N9 vaccine 1 week and 2 weeks post infection. The HI titer in the D-Tetra-Peptide Hydrogel adjuvant vaccine group was higher than that in the split H7N9 vaccine at 2 weeks post infection. Conclusion: The D/L Tetra-Peptide Hydrogels increased the protection of the H7N9 vaccine and could be promising adjuvants for H7N9 vaccines against highly pathogenic H7N9 virus.

Designing spatial and temporal control of vaccine responses

Vaccines are the key technology to combat existing and emerging infectious diseases. However, increasing the potency, quality and durability of the vaccine response remains a challenge. As our knowledge of the immune system deepens, it becomes clear that vaccine components must be in the right place at the right time to orchestrate a potent and durable response. Material platforms, such as nanoparticles, hydrogels and microneedles, can be engineered to spatially and temporally control the interactions of vaccine components with immune cells. Materials-based vaccination strategies can augment the immune response by improving innate immune cell activation, creating local inflammatory niches, targeting lymph node delivery and controlling the time frame of vaccine delivery, with the goal of inducing enhanced memory immunity to protect against future infections. In this Review, we highlight the biological mechanisms underlying strong humoral and cell-mediated immune responses and explore materials design strategies to manipulate and control these mechanisms.

Facile Preparation of Drug-Releasing Supramolecular Hydrogel for Preventing Postoperative Peritoneal Adhesion

Hydrogels have attracted widespread attention for breaking the bottlenecks faced during facile drug delivery. To date, the preparation of jelly carriers for hydrophobic drugs remains challenging. In this study, by evaporating ethanol to drive the formation of hydrogen bonds, hydrophilic poly(vinyl alcohol) (PVA) and certain hydrophobic compounds [luteolin (LUT), quercetin (QUE), and myricetin (MYR)] were rapidly prepared into supramolecular hydrogel within 10 min. The gelation performance of these three hydrogels changed regularly with the changing sequence of LUT, QUE, and MYR. An investigation of the gelation pathway of these hybrid gels reveals that the formation of this type of gel follows a simple supramolecular self-assembly process, called "hydrophobe-hydrophile crosslinked gelation". Because the hydrogen bond between PVA and the drug is noncovalent and reversible, the hydrogel has good plasticity and self-healing properties, while the drugs can be controllably released by tuning the output stimuli. Using a rat sidewall-cecum abrasion adhesion model, the as-prepared hydrogel was highly efficient and safe in preventing postsurgical adhesion. This work provides a useful archetypical template for researchers interested in the efficient delivery and controllable release of hydrophobic drugs.

Implantation of a neoantigen-targeted hydrogel vaccine prevents recurrence of pancreatic adenocarcinoma after incomplete resection

Tumor involvement of major vascular structures limits surgical options in pancreatic adenocarcinoma (PDAC), which in turn limits opportunities for cure. Despite advances in locoregional approaches, there is currently no role for incomplete resection. This study evaluated a gelatinized neoantigen-targeted vaccine applied to a grossly positive resection margin in preventing local recurrence. Incomplete surgical resection was performed in mice bearing syngeneic flank Panc02 tumors, leaving a 1 mm rim adherent to the muscle bed. A previously validated vaccine consisting of neoantigen peptides, a stimulator of interferon genes (STING) agonist and AddaVax^TM (termed PancVax) was embedded in a hyaluronic acid hydrogel and applied to the tumor bed. Tumor remnants, regional lymph nodes, and spleens were analyzed using histology, flow cytometry, gene expression profiling, and ELISPOT assays. The immune microenvironment at the tumor margin after surgery alone was characterized by a transient influx of myeloid-derived suppressor cells (MDSCs), prolonged neutrophil influx, and near complete loss of cytotoxic T cells. Application of PancVax gel was associated with enhanced T cell activation in the draining lymph node and expansion of neoantigen-specific T cells in the spleen. Mice implanted with PancVax gel demonstrated no evidence of residual tumor at two weeks postoperatively and healed incisions at two months postoperatively without local recurrence. In summary, application of PancVax gel at a grossly positive tumor margin led to systemic expansion of neoantigen-specific T cells and effectively prevented local recurrence. These findings support further work into locoregional adjuncts to immune modulation in PDAC.

Revolutionizing polymer-based nanoparticle-linked vaccines for targeting respiratory viruses: A perspective

Viral respiratory tract infections have significantly impacted global health as well as socio-economic growth. Respiratory viruses such as the influenza virus, respiratory syncytial virus (RSV), and the recent SARS-CoV-2 infection (COVID-19) typically infect the upper respiratory tract by entry through the respiratory mucosa before reaching the lower respiratory tract, resulting in respiratory disease. Generally, vaccination is the primary method in preventing virus pathogenicity and it has been shown to remarkably reduce the burden of various infectious diseases. Nevertheless, the efficacy of conventional vaccines may be hindered by certain limitations, prompting the need to develop novel vaccine delivery vehicles to immunize against various strains of respiratory viruses and to mitigate the risk of a pandemic. In this review, we provide an insight into how polymer-based nanoparticles can be integrated with the development of vaccines to effectively enhance immune responses for combating viral respiratory tract infections.

Modulation of injectable hydrogel properties for slow co-delivery of influenza subunit vaccine components enhance the potency of humoral immunity

Vaccines are critical for combating infectious diseases across the globe. Influenza, for example, kills roughly 500,000 people annually worldwide, despite annual vaccination campaigns. Efficacious vaccines must elicit a robust and durable antibody response, and poor efficacy often arises from inappropriate temporal control over antigen and adjuvant presentation to the immune system. In this work, we sought to exploit the immune system's natural response to extended pathogen exposure during infection by designing an easily administered slow-delivery influenza vaccine platform. We utilized an injectable and self-healing polymer-nanoparticle (PNP) hydrogel platform to prolong the co-delivery of vaccine components to the immune system. We demonstrated that these hydrogels exhibit unique dynamic physical characteristics whereby physicochemically distinct influenza hemagglutinin antigen and a toll-like receptor 7/8 agonist adjuvant could be co-delivered over prolonged timeframes that were tunable through simple alteration of the gel formulation. We show a relationship between hydrogel physical properties and the resulting immune response to immunization. When administered in mice, hydrogel-based vaccines demonstrated enhancements in the magnitude and duration of humoral immune responses compared to alum, a widely used clinical adjuvant system. We found stiffer hydrogel formulations exhibited slower release and resulted in the greatest improvements to the antibody response while also enabling significant adjuvant dose sparing. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.