Immunogenicity of pulsatile-release PLGA microspheres for single-injection vaccination

A single-injection vaccine providing protection against two HPV types

Prophylactic human papillomavirus (HPV) vaccines against cervical cancer were successfully developed; however, challenges such as high cost and low compliance still remain to be overcome. In addition, because many HPV types can cause cervical cancer, antigens of multiple HPV types are needed to achieve broad protection. In this study, a bivalent single-injection HPV vaccine was designed in which virus-like particles (VLPs) of HPV 16 L1 and HPV 18 L1 were used as antigens. A recently developed drug carrier that uses tannic acid/polyethylene glycol films as the erodible layer was employed to accomplish multiple pulsatile releases of the antigens. Monovalent single-injection vaccines for HPV 16 and HPV 18 were first designed. A bivalent single-injection vaccine was then obtained by simply mixing the two monovalent vaccines. The bivalent vaccine provided protection against both HPV types. More importantly, it elicited both humoral and cellular immune responses as potent as those elicited by the corresponding multiple dose vaccine because of their similar release profile of antigens. Cross-reactivity was observed between HPV 16 and 18 in terms of cellular immune responses, while no cross-reactivity was found in terms of humoral immune responses. Note that other multivalent single-injection vaccines could be designed in the same way. These vaccines are expected to help prevent cervical cancer because of their broad protection, enhanced compliance and lowered vaccination cost.

Recent Applications of PLGA in Drug Delivery Systems

Poly(lactic-co-glycolic acid) (PLGA) is a widely used biodegradable and biocompatible copolymer in drug delivery systems (DDSs). In this article, we highlight the critical physicochemical properties of PLGA, including its molecular weight, intrinsic viscosity, monomer ratio, blockiness, and end caps, that significantly influence drug release profiles and degradation times. This review also covers the extensive literature on the application of PLGA in delivering small-molecule drugs, proteins, peptides, antibiotics, and antiviral drugs. Furthermore, we discuss the role of PLGA-based DDSs in the treating various diseases, including cancer, neurological disorders, pain, and inflammation. The incorporation of drugs into PLGA nanoparticles and microspheres has been shown to enhance their therapeutic efficacy, reduce toxicity, and improve patient compliance. Overall, PLGA-based DDSs holds great promise for the advancement of the treatment and management of multiple chronic conditions.

Demonstration of Tunable Control over a Delayed-Release Vaccine Using Atomic Layer Deposition

Many vaccines require multiple doses for full efficacy, posing a barrier for patient adherence and protection. One solution to achieve full vaccination may be attained with single-administration vaccines containing multiple controlled release doses. In this study, delayed-release vaccines were generated using atomic layer deposition (ALD) to coat antigen-containing powders with alumina. Using in vitro and in vivo methods, we show that increasing the coat thickness controls the kinetics of antigen release and antibody response, ranging from weeks to months. Our results establish an in vitro-in vivo correlation with a level of tunable control over the antigen release and antibody response times with the potential to impact future vaccine design.

Prolonged delivery of HIV-1 vaccine nanoparticles from hydrogels

Immunization is a straightforward concept but remains for some pathogens like HIV-1 a challenge. Thus, new approaches towards increasing the efficacy of vaccines are required to turn the tide. There is increasing evidence that antigen exposure over several days to weeks induces a much stronger and more sustained immune response compared to traditional bolus injection, which usually leads to antigen elimination from the body within a couple of days. Therefore, we developed a poly(ethylene) glycol (PEG) hydrogel platform to investigate the principal feasibility of a sustained release of antigens to mimic natural infection kinetics. Eight-and four-armed PEG macromonomers of different MWs (10, 20, and 40 kDa) were end-group functionalized to allow for hydrogel formation via covalent cross-linking. An HIV-1 envelope (Env) antigen in its trimeric (Envtri) or monomeric (Envmono) form was applied. The soluble Env antigen was compared to a formulation of Env attached to silica nanoparticles (Env-SiNPs). The latter are known to have a higher immunogenicity compared to their soluble counterparts. Hydrogels were tunable regarding the rheological behavior allowing for different degradation times and release timeframes of Env-SiNPs over two to up to 50 days. Affinity measurements of the VCR01 antibody which specifically recognizes the CD4 binding site of Env, revealed that neither the integrity nor the functionality of Envmono-SiNPs (Kd = 2.1 ± 0.9 nM) and Envtri-SiNPs (Kd = 1.5 ± 1.3 nM), respectively, were impaired after release from the hydrogel (Kd before release: 2.1 ± 0.1 and 7.8 ± 5.3 nM, respectively). Finally, soluble Env and Env-SiNPs which are two physico-chemically distinct compounds, were co-delivered and shown to be sequentially released from one hydrogel which could be beneficial in terms of heterologous immunization or single dose vaccination. In summary, this study presents a tunable, versatile applicable, and effective delivery platform that could improve vaccination effectiveness also for other infectious diseases than HIV-1.

Self-Assembled PLGA-Pluronic F127 Microsphere for Sustained Drug Release for Osteoarthritis

For many years, sustained-release drug delivery systems (SRDDS) have emerged as a featured topic in the pharmaceutical field. Particularly for chronic diseases, such as osteoarthritis, there is a lot of demand for SRDDS because of the long treatment period and repetitive medication administration. Thus, we developed an injectable PLGA-F127 microsphere (MS) that is capable of the in situ conversion to an implant. The microprecipitation method for PLGA-F127 MS was established, and the physicochemical stability of the products was confirmed. The microspheres were assembled into a single mass in 37 °C aqueous conditions and showed a remarkably delayed drug release profile. First, the release started with no significant initial burst and lagged for 60 days. After that, in the next 40 days, the remaining 75% of the drugs were constantly released until day 105. We expect that our PLGA-F127 MS could be employed to extend the release period of 2 months of medication to 4 months. This could be a valuable solution for developing novel SRDDS for local injections.

Single-injection subunit vaccine for rabies prevention using lentinan as adjuvant

Current rabies vaccines require 5 doses to provide full protection from the deadly virus, which significantly reduce the compliance of recipients. To minimize the number of immunizations herein single injection vaccines were developed. First a single injection vaccine was designed using rabies virus glycoprotein (G protein) as antigen. A time-controlled release system which uses dynamic layer-by-layer films as erodible coating was employed to accomplish multiply pulsatile releases of G protein. The single-injection vaccine elicits potent humoral and cellular immune responses comparable to the corresponding multi-dose ordinary vaccines because of their similar release pattern of G protein. To further improve its performance, a second single injection vaccine, in which lentinan was added as adjuvant, was designed. This single-injection vaccine again elicits humoral and cellular immune responses comparable to the corresponding multi-dose ordinary vaccines because of their similar release pattern of antigen and adjuvant. In addition, the second single-injection vaccine elicits higher level immune response and provides higher efficiency on virus inhibition than the first one because lentinan can booster immune response.

Exponentially decreasing exposure of antigen generates anti-inflammatory T-cell responses

Rheumatoid Arthritis (RA) is a chronic debilitating disease characterized by auto-immune reaction towards self-antigen such as collagen type II. In this study, we investigated the impact of exponentially decreasing levels of antigen exposure on pro-inflammatory T cell responses in the collagen-induced arthritis (CIA) mouse model. Using a controlled delivery experimental approach, we manipulated the collagen type II (CII) antigen concentration presented to the immune system. We observed that exponentially decreasing levels of antigen generated reduced pro-inflammatory T cell responses in secondary lymphoid organs in mice suffering from RA. Specifically, untreated mice exhibited robust pro-inflammatory T cell activation and increased paw inflammation, whereas, mice exposed to exponentially decreasing concentrations of CII demonstrated significantly reduced pro-inflammatory T cell responses, exhibited lower levels of paw inflammation, and decreased arthritis scores in right rear paw. The data also demonstrate that the decreasing antigen levels promoted the induction of regulatory T cells (Tregs), which play a crucial role in maintaining immune tolerance and suppressing excessive inflammatory responses. Our findings highlight the importance of antigen concentration in modulating pro-inflammatory T cell responses in the CIA model. These results provide valuable insights into the potential therapeutic strategies that target antigen presentation to regulate immune responses and mitigate inflammation in rheumatoid arthritis and other autoimmune diseases. Further investigations are warranted to elucidate the specific mechanisms underlying the antigen concentration-dependent modulation of T cell responses and to explore the translational potential of this approach for the development of novel therapeutic interventions in autoimmune disorders.

Advanced subunit vaccine delivery technologies: From vaccine cascade obstacles to design strategies

Designing and manufacturing safe and effective vaccines is a crucial challenge for human health worldwide. Research on adjuvant-based subunit vaccines is increasingly being explored to meet clinical needs. Nevertheless, the adaptive immune responses of subunit vaccines are still unfavorable, which may partially be attributed to the immune cascade obstacles and unsatisfactory vaccine design. An extended understanding of the crosstalk between vaccine delivery strategies and immunological mechanisms could provide scientific insight to optimize antigen delivery and improve vaccination efficacy. In this review, we summarized the advanced subunit vaccine delivery technologies from the perspective of vaccine cascade obstacles after administration. The engineered subunit vaccines with lymph node and specific cell targeting ability, antigen cross-presentation, T cell activation properties, and tailorable antigen release patterns may achieve effective immune protection with high precision, efficiency, and stability. We hope this review can provide rational design principles and inspire the exploitation of future subunit vaccines.

Effect of polycation coating on the long-term pulsatile release of antigenic ESAT-61-20 peptide from PLGA nanoparticles

The development of novel vaccine formulations against tuberculosis is necessary to reduce the number of new cases worldwide. Polymeric nanoparticles offer great potential as antigen delivery and immunostimulant systems for such purposes. In the study, we have encapsulated the antigenic peptide epitope of ESAT-6 protein of M. tuberculosis into PLGA nanoparticles and coated these nanoparticles with the cationic polymer of quaternized poly(4-vinylpyridine) (QPVP) to obtain a positively charged system as a potential nasal vaccine prototype. The produced spherical nanoparticles had hydrodynamic diameters between 180 and 240 nm with a narrow size distribution. The non-coated nanoparticle exhibited a 3-phase in vitro release profile that was completed in more than 4 months. In this release study, 5% of the peptide was released in the first 6 h and the nanoparticle remained silent until the 70th day. Then, an additional 5% of the peptide was released in 45 days. After coating the nanoparticle with QPVP, the release periods and peptide amounts dramatically changed. The antigenic peptide-loaded nanoparticles coated with the polycation stimulated the macrophages in vitro to release more nitric oxide (NO) compared to the free peptide and non-coated nanoparticle, which reveals the immunostimulant activity of the produced nanoparticle systems. The produced non-coated nanoparticles with the prolonged pulsatile release of the antigenic peptide can be used in the development of single injection self-boosting vaccine formulations. By coating these nanoparticles, both the release profile and immunogenicity can be changed.

Overcoming barriers to patient adherence: the case for developing innovative drug delivery systems

Poor medication adherence is a pervasive issue with considerable health and socioeconomic consequences. Although the underlying reasons are generally understood, traditional intervention strategies rooted in patient-centric education and empowerment have proved to be prohibitively complex and/or ineffective. Formulating a pharmaceutical in a drug delivery system (DDS) is a promising alternative that can directly mitigate many common impediments to adherence, including frequent dosing, adverse effects and a delayed onset of action. Existing DDSs have already positively influenced patient acceptability and improved rates of adherence across various disease and intervention types. The next generation of systems have the potential to instate an even more radical paradigm shift by, for example, permitting oral delivery of biomacromolecules, allowing for autonomous dose regulation and enabling several doses to be mimicked with a single administration. Their success, however, is contingent on their ability to address the problems that have made DDSs unsuccessful in the past.

Multipolymer microsphere delivery of SARS-CoV-2 antigens

Effective antigen delivery facilitates antiviral vaccine success defined by effective immune protective responses against viral exposures. To improve severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antigen delivery, a controlled biodegradable, stable, biocompatible, and nontoxic polymeric microsphere system was developed for chemically inactivated viral proteins. SARS-CoV-2 proteins encapsulated in polymeric microspheres induced robust antiviral immunity. The viral antigen-loaded microsphere system can preclude the need for repeat administrations, highlighting its potential as an effective vaccine. STATEMENT OF SIGNIFICANCE: Successful SARS-CoV-2 vaccines were developed and quickly approved by the US Food and Drug Administration (FDA). However, each of the vaccines requires boosting as new variants arise. We posit that injectable biodegradable polymers represent a means for the sustained release of emerging viral antigens. The approach offers a means to reduce immunization frequency by predicting viral genomic variability. This strategy could lead to longer-lasting antiviral protective immunity. The current proof-of-concept multipolymer study for SARS-CoV-2 achieve these metrics.

A Single Injection with Sustained-Release Microspheres and a Prime-Boost Injection of Bovine Serum Albumin Elicit the Same IgG Antibody Response in Mice

Although vaccination is still considered to be the cornerstone of public health care, the increase in vaccination coverage has stagnated for many diseases. Most of these vaccines require two or three doses to be administered across several months or years. Single-injection vaccine formulations are an effective method to overcome the logistical barrier to immunization that is posed by these multiple-injection schedules. Here, we developed subcutaneously (s.c.) injectable microspheres with a sustained release of the model antigen bovine serum albumin (BSA). The microspheres were composed of blends of two novel biodegradable multi-block copolymers consisting of amorphous, hydrophilic poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL) blocks and semi-crystalline poly(dioxanone) (PDO) blocks of different block sizes. In vitro studies demonstrated that the release of BSA could be tailored over a period of approximately four to nine weeks by changing the blend ratio of both polymers. Moreover, it was found that BSA remained structurally intact during release. Microspheres exhibiting sustained release of BSA for six weeks were selected for the in vivo study in mice. The induced BSA-specific IgG antibody titers increased up to four weeks after administration and were of the same magnitude as found in mice that received a priming and a booster dose of BSA in phosphate-buffered saline (PBS). Determination of the BSA concentration in plasma showed that in vivo release probably took place up to at least four weeks, although plasma concentrations peaked already one week after administration. The sustained-release microspheres might be a viable alternative to the conventional prime-boost immunization schedule, but a clinically relevant antigen should be incorporated to assess the full potential of these microspheres in practice.

Polymeric nanoparticle-based nanovaccines for cancer immunotherapy

Therapeutic cancer vaccines, which are designed to amplify tumor-specific T cell responses, have been envisioned as one of the most powerful tools for effective cancer immunotherapy. However, increasing the potency, quality and durability of the vaccine response remains a big challenge. In recent years, materials-based delivery systems focusing on the co-delivery of antigens and adjuvants to enhance cancer vaccination therapy have attracted increasing interest. Among various materials, polymeric nanoparticles (NPs) with different physicochemical properties which can incorporate multiple immunological cues are of great interest. In this review, the recent progress in the design and construction of both ex vivo subunit and in situ cancer vaccines using polymeric NPs is summarized. Especially, we will focus on how these NPs improve the adjuvanticity of vaccines. The design principles of polymeric NPs for ex vivo subunit cancer vaccines and in situ cancer vaccination are also discussed. Finally, we want to briefly discuss molecular chaperones in cancer immunity and the applications of our unique self-assembly mixed shell polymeric micelle-based nanochaperones for cancer vaccines.

Naringenin Microsphere as a Novel Adjuvant Reverses Colistin Resistance via Various Strategies against Multidrug-Resistant Klebsiella pneumoniae Infection

The efficacy of colistin, the last option against multidrug-resistant (MDR) Gram-negative bacteria, is severely threatened by the prevalence of plasmid- or chromosome-mediated colistin resistance genes. Herein, naringenin has dramatically restored colistin sensitivity against colistin-resistant Klebsiella pneumoniae infection without affecting bacterial viability, inducing resistance and causing obvious cell toxicity. Mechanism analysis reveals that naringenin potentiates colistin activity by multiple strategies including inhibition of mobilized colistin resistance gene activity, repression of two-component system regulation, and acceleration of reactive oxygen species-mediated oxidative damage. A lung-targeted delivery system of naringenin microspheres has been designed to facilitate naringenin bioavailability, accompanied by an effective potentiation of colistin for Klebsiella pneumoniae infection. Consequently, a new recognition of naringenin microspheres has been elucidated to restore colistin efficacy against colistin-resistant Gram-negative pathogens, which may be an effective strategy of developing potential candidates for MDR Gram-negative bacteria infection.

Single-injection COVID-19 subunit vaccine elicits potent immune responses

Current vaccination schedules, including COVID-19 vaccines, require multiple doses to be administered. Single injection vaccines eliciting equivalent immune response are highly desirable. Unfortunately because unconventional release kinetics are difficult to achieve it still remains a huge challenge. Herein a single-injection COVID-19 vaccine was designed using a highly programmable release system based on dynamic layer-by-layer (LBL) films. The antigen, S1 subunit of SARS-CoV-2 spike protein, was loaded in CaCO₃ microspheres, which were further coated with tannic acid (TA)/polyethylene glycol (PEG) LBL films. The single-injection vaccine was obtained by mixing the microspheres coated with different thickness of TA/PEG films. Because of the unique constant-rate erosion behavior of the TA/PEG coatings, this system allows for distinct multiple pulsatile release of antigen, closely mimicking the release profile of antigen in conventional multiple dose vaccines. Immunization with the single injection vaccine induces potent and persistent S1-specific humoral and cellular immune responses in mice. The sera from the vaccinated animal exhibit robust in vitro viral neutralization ability. More importantly, the immune response and viral inhibition induced by the single injection vaccine are as strong as that induced by the corresponding multiple dose vaccine, because they share the same antigen release profile. STATEMENT OF SIGNIFICANCE: Vaccines are the most powerful and cost-effective weapons against infectious diseases such as COVID-19. However, current vaccination schedules, including the COVID-19 vaccines, require multiple doses to be administered. Herein a single-injection COVID-19 vaccine is designed using a highly programmable release system. This vaccine releases antigens in a pulsatile manner, closely mimicking the release pattern of antigens in conventional multiple dose vaccines. As a result, one single injection of the new vaccine induces an immune response and viral inhibition similar to that induced by the corresponding multiple-dose vaccine approach.

Construction of single-injection vaccine using new time-controlled release system

Single-injection vaccines may overcome issues, such as high cost and poor patient compliance, of the multi-bolus regimes dominantly used in vaccination. However no such vaccine has been commercialized because time-controlled release, an unconventional release kinetics, is difficult to achieve. Here a new time-controlled release system using dynamic layer-by-layer (LBL) film as erodible coating was used to design single-injection vaccine. Unlike commonly used degradable polymers, dynamic LBL film disintegrates at a constant rate, thus allowing distinct pulsatile release of antigen at predetermined intervals. The release pattern of the single-injection vaccine mimics closely to that of ordinary multi-dose regimes. It elicits both humoral and cellular immune responses which are comparable to or even stronger than the corresponding multi-dose regime. In addition, it inhibits tumor growth more effectively. The new vaccine will not only improve patient compliance but also therapeutic outcome.

Fighting type 2 diabetes: Formulation strategies for peptide-based therapeutics

Diabetes mellitus is a major health problem with increasing prevalence at a global level. The discovery of insulin in the early 1900s represented a major breakthrough in diabetes management, with further milestones being subsequently achieved with the identification of glucagon-like peptide-1 (GLP-1) and the introduction of GLP-1 receptor agonists (GLP-1 RAs) in clinical practice. Moreover, the subcutaneous delivery of biotherapeutics is a well-established route of administration generally preferred over the intravenous route due to better patient compliance and prolonged drug absorption. However, current subcutaneous formulations of GLP-1 RAs present pharmacokinetic problems that lead to adverse reactions and treatment discontinuation. In this review, we discuss the current challenges of subcutaneous administration of peptide-based therapeutics and provide an overview of the formulations available for the different routes of administration with improved bioavailability and reduced frequency of administration.

Lung-Targeting Lysostaphin Microspheres for Methicillin-Resistant Staphylococcus aureus Pneumonia Treatment and Prevention

Multifunctional antimicrobial strategies are urgently needed to treat methicillin-resistant Staphylococcus aureus (MRSA) caused pneumonia due to its increasing resistance, enhanced virulence, and high pathogenicity. Here, we report that lysostaphin, a bacteriolytic enzyme, encapsulated within poly(lactic-co-glycolic acid) microspheres (LyIR@MS) specially treats planktonic MRSA bacteria, mature biofilms, and related pneumonia. Optimized LyIR@MS with suitable diameters could deliver a sufficient amount of lysostaphin to the lung without a decrease in survival rate after intravenous injection. Furthermore, the degradable properties of the carrier make it safe for targeted release of lysostaphin to eliminate MRSA, repressing the expression of virulence genes and improving the sensitivity of biofilms to host neutrophils. In the MRSA pneumonia mouse model, treatment or prophylaxis with LyIR@MS significantly improved survival rate and relieved inflammatory injury without introducing adverse events. These findings suggest the clinical translational potential of LyIR@MS for the treatment of MRSA-infected lung diseases.

Biomaterials and nanomaterials for sustained release vaccine delivery

Vaccines are considered one of the most significant medical advancements in human history, as they have prevented hundreds of millions of deaths since their discovery; however, modern travel permits disease spread at unprecedented rates, and vaccine shortcomings like thermal sensitivity and required booster shots have been made evident by the COVID-19 pandemic. Approaches to overcoming these issues appear promising via the integration of vaccine technology with biomaterials, which offer sustained-release properties and preserve proteins, prevent conformational changes, and enable storage at room temperature. Sustained release and thermal stabilization of therapeutic biomacromolecules is an emerging area that integrates material science, chemistry, immunology, nanotechnology, and pathology to investigate different biocompatible materials. Biomaterials, including natural sugar polymers, synthetic polyesters produced from biologically derived monomers, hydrogel blends, protein-polymer blends, and metal-organic frameworks, have emerged as early players in the field. This overview will focus on significant advances of sustained release biomaterial in the context of vaccines against infectious disease and the progress made towards thermally stable "single-shot" formulations. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Hitchhiking on Controlled-Release Drug Delivery Systems: Opportunities and Challenges for Cancer Vaccines

Cancer vaccines represent among the most promising strategies in the battle against cancers. However, the clinical efficacy of current cancer vaccines is largely limited by the lack of optimized delivery systems to generate strong and persistent antitumor immune responses. Moreover, most cancer vaccines require multiple injections to boost the immune responses, leading to poor patient compliance. Controlled-release drug delivery systems are able to address these issues by presenting drugs in a controlled spatiotemporal manner, which allows co-delivery of multiple drugs, reduction of dosing frequency and avoidance of significant systemic toxicities. In this review, we outline the recent progress in cancer vaccines including subunit vaccines, genetic vaccines, dendritic cell-based vaccines, tumor cell-based vaccines and in situ vaccines. Furthermore, we highlight the efforts and challenges of controlled or sustained release drug delivery systems (e.g., microparticles, scaffolds, injectable gels, and microneedles) in ameliorating the safety, effectiveness and operability of cancer vaccines. Finally, we briefly discuss the correlations of vaccine release kinetics and the immune responses to enlighten the rational design of the next-generation platforms for cancer therapy.

Engineering Vaccines for Tissue-Resident Memory T Cells

In recent years, tissue-resident memory T cells (TRM) have attracted significant attention in the field of vaccine development. Distinct from central and effector memory T cells, TRM cells take up residence in home tissues such as the lung or urogenital tract and are ideally positioned to respond quickly to pathogen encounter. TRM have been found to play a role in the immune response against many globally important infectious diseases for which new or improved vaccines are needed, including influenza and tuberculosis. It is also increasingly clear that TRM play a pivotal role in cancer immunity. Thus, vaccines that can generate this memory T cell population are highly desirable. The field of immunoengineering-that is, the application of engineering principles to study the immune system and design new and improved therapies that harness or modulate immune responses-is ideally poised to provide solutions to this need for next-generation TRM vaccines. This review covers recent developments in vaccine technologies for generating TRM and protecting against infection and cancer, including viral vectors, virus-like particles, and synthetic and natural biomaterials. In addition, it offers critical insights on the future of engineering vaccines for tissue-resident memory T cells.

Microarray patches enable the development of skin-targeted vaccines against COVID-19

The COVID-19 pandemic is a serious threat to global health and the global economy. The ongoing race to develop a safe and efficacious vaccine to prevent infection by SARS-CoV-2, the causative agent for COVID-19, highlights the importance of vaccination to combat infectious pathogens. The highly accessible cutaneous microenvironment is an ideal target for vaccination since the skin harbors a high density of antigen-presenting cells and immune accessory cells with broad innate immune functions. Microarray patches (MAPs) are an attractive intracutaneous biocargo delivery system that enables safe, reproducible, and controlled administration of vaccine components (antigens, with or without adjuvants) to defined skin microenvironments. This review describes the structure of the SARS-CoV-2 virus and relevant antigenic targets for vaccination, summarizes key concepts of skin immunobiology in the context of prophylactic immunization, and presents an overview of MAP-mediated cutaneous vaccine delivery. Concluding remarks on MAP-based skin immunization are provided to contribute to the rational development of safe and effective MAP-delivered vaccines against emerging infectious diseases, including COVID-19.

Effects on immunization of the physicochemical parameters of particles as vaccine carriers

Vaccination has milestone significance for the prophylactic and complete elimination of infectious diseases. However, combating malignant infectious diseases, such as Ebola or HIV, remains a challenge. It is necessary to explore novel technologies to facilitate the immune profile of vaccines. Particles exhibit a remarkable ability to modulate sophisticated immunity because of their intrinsic adjuvanticity or codelivery with immunostimulatory molecules. Recently, particles have been broadly investigated as carriers for vaccine delivery. Their physicochemical parameters (e.g., size, shape, and surface chemistry) significantly influence their in vivo fate and subsequent immunization effect. Herein, we highlight several types of particulate carrier used in the delivery of vaccines. We also examine how to engineer the physical and chemical characteristics of particulate adjuvants to make them robust candidates for a versatile vaccine delivery platform.

Improving pandemic preparedness through better, faster influenza vaccines

Introduction. Timely availability of effective influenza vaccine will be critical to mitigate the next influenza pandemic. The mission of Biomedical Advanced Research and Development Authority (BARDA) is to develop medical countermeasures against pandemics, including influenza and other health security threats.Areas covered. Despite considerable gains in pandemic vaccine preparedness since 2009, old and new challenges threaten the pandemic influenza response capabilities of the U.S. Government: insufficient U.S.-based vaccine production, two-dose vaccination regimen, logistically complex adjuvanted formulation, and sustained surge manufacturing capacity despite no commercial market for pandemic vaccines. Although the coronavirus disease 2019 (COVID-19) pandemic has re-exposed these gaps in preparedness and response, previous investments into flexible influenza vaccine technologies proved to be critical to accelerate COVID-19 vaccine development.Expert opinion. BARDA addresses these challenges by implementing a pandemic influenza vaccine strategy with two key goals: 1) accelerating vaccine development and production (faster) and 2) improving vaccine performance (better). This strategy involves an end-to-end approach, including increasing manufacturing and fill-finish capacity; improving release testing speed; and funding clinical trials to improve current vaccine utilization. As demonstrated by the COVID-19 response, continued investments into this pandemic influenza vaccine strategy will further enhance the ability to respond to future emerging pandemic pathogens.

Emerging skin-targeted drug delivery strategies to engineer immunity: A focus on infectious diseases

INTRODUCTION

Infectious pathogens are global disrupters. Progress in biomedical science and technology has expanded the public health arsenal against infectious diseases. Specifically, vaccination has reduced the burden of infectious pathogens. Engineering systemic immunity by harnessing the cutaneous immune network has been particularly attractive since the skin is an easily accessible immune-responsive organ. Recent advances in skin-targeted drug delivery strategies have enabled safe, patient-friendly, and controlled deployment of vaccines to cutaneous microenvironments for inducing long-lived pathogen-specific immunity to mitigate infectious diseases, including COVID-19.

AREAS COVERED

This review briefly discusses the basics of cutaneous immunomodulation and provides a concise overview of emerging skin-targeted drug delivery systems that enable safe, minimally invasive, and effective intracutaneous administration of vaccines for engineering systemic immune responses to combat infectious diseases.

EXPERT OPINION

In-situ engineering of the cutaneous microenvironment using emerging skin-targeted vaccine delivery systems offers remarkable potential to develop diverse immunization strategies against pathogens. Mechanistic studies with standard correlates of vaccine efficacy will be important to compare innovative intracutaneous drug delivery strategies to each other and to existing clinical approaches. Cost-benefit analyses will be necessary for developing effective commercialization strategies. Significant involvement of industry and/or government will be imperative for successfully bringing novel skin-targeted vaccine delivery methods to market for their widespread use.

Leveraging the modularity of biomaterial carriers to tune immune responses

Biomaterial carriers offer modular features to control the delivery and presentation of vaccines and immunotherapies. This tunability is a distinct capability of biomaterials. Understanding how tunable material features impact immune responses is important to improve vaccine and immunotherapy design, as well as clinical translation. Here we discuss the modularity of biomaterial properties as a means of controlling encounters with immune signals across scales - tissue, cell, molecular, and time - and ultimately, to direct stimulation or regulation of immune function. We highlight these advances using illustrations from recent literature across infectious disease, cancer, and autoimmunity. As the immune engineering field matures, informed design criteria could support more rational biomaterial carriers for vaccination and immunotherapy.

Microneedles with dual release pattern for improved immunological efficacy of Hepatitis B vaccine

In this study, dissolving microneedles (DMNs) with dual-release pattern, capable of both bolus release and slow release, were prepared. These DMNs were used with a hepatitis B vaccine that requires multiple shots to achieve immunological efficacy comparable to that obtained when two separate shots are administered. Dissolving microneedles with HBsAg in PLA tips and CMC coating formulation together (HBsAg-PLA/CMC-DMNs) consist of polylactic acid (PLA) tips for slow release, a carboxy-methyl cellulose (CMC) coating formulation for bolus release, and a dissolving base of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) for dissolution in the skin. The in vitro release pattern of HBsAg from the CMC coating formulation and PLA tips was observed. Through an in vivo test, 1) the delivery efficiency of HBsAg-PLA/CMC-DMNs was observed, and 2) the immunological efficacy of this method was compared with the efficacy of two shots delivered by conventional intramuscular (IM) administration and two shots delivered by HBsAg-coated microneedle (CMNs) administration. HBsAg-PLA/CMC-DMNs punctured the skin successfully. The PVA/PVP base was completely dissolved within 10 min of insertion, resulting in the delivery of all microneedle tips into the skin. In the in vitro release experiment, all of the HBsAg in the CMC coating formulation was released within 20 min, and the HBsAg present in the PLA tips was gradually released over more than 55 days. The antibody titer of one shot of HBsAg-PLA/CMC-DMNs was the same as or higher than two shots delivered by conventional IM and CMN methods. DMNs with dual-release pattern can deliver two formulations simultaneously with a single shot, resulting in improved immunological efficacy of HBsAg that requires multiple doses. In addition, this dual-release MN system can be used for the delivery of other drugs that require multiple administrations.

Technological approaches to streamline vaccination schedules, progressing towards single-dose vaccines

Vaccines represent the most successful medical intervention in history, with billions of lives saved. Although multiple doses of the same vaccine are typically required to reach an adequate level of protection, it would be advantageous to develop vaccines that induce protective immunity with fewer doses, ideally just one. Single-dose vaccines would be ideal to maximize vaccination coverage, help stakeholders to greatly reduce the costs associated with vaccination, and improve patient convenience. Here we describe past attempts to develop potent single dose vaccines and explore the reasons they failed. Then, we review key immunological mechanisms of the vaccine-specific immune responses, and how innovative technologies and approaches are guiding the preclinical and clinical development of potent single-dose vaccines. By modulating the spatio-temporal delivery of the vaccine components, by providing the appropriate stimuli to the innate immunity, and by designing better antigens, the new technologies and approaches leverage our current knowledge of the immune system and may synergize to enable the rational design of next-generation vaccination strategies. This review provides a rational perspective on the possible development of future single-dose vaccines.

Controlling timing and location in vaccines

Vaccines are one of the most powerful technologies supporting public health. The adaptive immune response induced by immunization arises following appropriate activation and differentiation of T and B cells in lymph nodes. Among many parameters impacting the resulting immune response, the presence of antigen and inflammatory cues for an appropriate temporal duration within the lymph nodes, and further within appropriate subcompartments of the lymph nodes- the right timing and location- play a critical role in shaping cellular and humoral immunity. Here we review recent advances in our understanding of how vaccine kinetics and biodistribution impact adaptive immunity, and the underlying immunological mechanisms that govern these responses. We discuss emerging approaches to engineer these properties for future vaccines, with a focus on subunit vaccines.

Technological Approaches for Improving Vaccination Compliance and Coverage

Vaccination has been well recognised as a critically important tool in preventing infectious disease, yet incomplete immunisation coverage remains a major obstacle to achieving disease control and eradication. As medical products for global access, vaccines need to be safe, effective and inexpensive. In line with these goals, continuous improvements of vaccine delivery strategies are necessary to achieve the full potential of immunisation. Novel technologies related to vaccine delivery and route of administration, use of advanced adjuvants and controlled antigen release (single-dose immunisation) approaches are expected to contribute to improved coverage and patient compliance. This review discusses the application of micro- and nano-technologies in the alternative routes of vaccine administration (mucosal and cutaneous vaccination), oral vaccine delivery as well as vaccine encapsulation with the aim of controlled antigen release for single-dose vaccination.

Development of an antimicrobial peptide-loaded mineralized collagen bone scaffold for infective bone defect repair

The repair of infective bone defects is a great challenge in clinical work. It is of vital importance to develop a kind of bone scaffold with good osteogenic properties and long-term antibacterial activity for local anti-infection and bone regeneration. A porous mineralized collagen (MC) scaffold containing poly(d,l-lactide-co-glycolic acid) (PLGA) microspheres loaded with two antibacterial synthetic peptides, Pac-525 or KSL-W was developed and characterized via scanning electron microscopy (SEM), porosity measurement, swelling and mechanical tests. The results showed that the MC scaffold embedded with smooth and compact PLGA microspheres had a positive effect on cell growth and also had antibacterial properties. Through toxicity analysis, cell morphology and proliferation analysis and alkaline phosphatase evaluation, the antibacterial scaffolds showed excellent biocompatibility and osteogenic activity. The antibacterial property evaluated with Staphylococcus aureus and Escherichia coli suggested that the sustained release of Pac-525 or KSL-W from the scaffolds could inhibit the bacterial growth aforementioned in the long term. Our results suggest that the antimicrobial peptides-loaded MC bone scaffold has good antibacterial and osteogenic activities, thus providing a great promise for the treatment of infective bone defects.

Particulate carrier systems as adjuvants for cancer vaccines

To overcome the immunosuppressive milieu of malignancy and lack of well-defined antigens, potent adjuvants are needed for cancer immunotherapy. Numerous small molecular immunomodulators have the potential to fulfill this role. To enhance the immune response and decrease the toxicity, particulate systems including nanoparticles and macroparticles have been increasingly proposed as carriers for cancer antigen and adjuvant delivery. These systems have the potential to co-deliver the antigens and adjuvants simultaneously in the same particle. In addition, the particles can be engineered for localized and targeted delivery, whether it be to the cellular or sub-cellular level. These properties limit systemic side effects and improve delivery efficiency, and thus enhance the vaccine's immune response. In particular, the particles can be constructed to mimic the size and surface patterns of microbes, organisms to which we have evolved a strong immune response. The release characteristics of the particles can likewise be controlled to simulate the body's response to infections. Boosting the immune response of vaccines by virtue of their intrinsic immunostimulatory properties, these particles can be dosing-sparing and have the potential to reduce production cost of vaccines. As the interest in personalized cancer vaccines increases with their encouraging outcomes in clinical trials, particulate carrier systems have the potential to play an important role in optimizing cancer vaccines.

Synthesis and Characterization of Rapidly Degrading Polyanhydrides as Vaccine Adjuvants

There is a currently a need to develop adjuvants that are best suited to simultaneously enhance immune responses, induce immunologic memory, improve patient compliance (i.e., reduce doses and inflammation), and provide vaccine shelf stability for stockpiling and global deployment to challenging environments. Biodegradable polyanhydrides have been investigated extensively to overcome such challenges. It has been shown that controlling copolymer composition can result in chemistry-dependent immunomodulatory capabilities. These studies have revealed that copolymers rich in sebacic acid (SA) are highly internalized by antigen presenting cells and confer improved shelf stability of encapsulated proteins, while copolymers rich in 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) also exhibit enhanced internalization by and activation of antigen presenting cells (APCs), in addition to providing superior retention of protein stability following encapsulation and release. However, to date, CPTEG:SA copolymers have not been synthesized and described. In this work, we hypothesized that new copolymers composed of CPTEG and SA would combine the advantages of both monomers in terms of enhanced thermal properties, maintaining antigenicity of encapsulated proteins following nanoparticle synthesis, and superior cellular internalization and activation by APCs, demonstrated by the upregulation of costimulatory markers CD80, CD86, and CD40, as well as the secretion of proinflammatory cytokines IL-6, IL-1β, and TNF-α. Herein, we describe the synthesis and design of novel CPTEG:SA nanoparticles with improved thermal properties, payload stability, and internalization by antigen presenting cells for applications in vaccine delivery. The performance of these new CPTEG:SA formulations was compared to that of traditional polyanhydride copolymers.

Nanoscale cationic micelles of amphiphilic copolymers based on star-shaped PLGA and PEI cross-linked PEG for protein delivery application

To enhance the bioavailability of protein therapeutants and improve the stability of storage and delivery, a series of branched amphiphilic block copolymers consisting of cholic acid (CA) initiated poly(D,L-lactide-co-glycolide) (CA-PLGA) and water-soluble polyethyleneimine cross-linked polyethylene glycol (PEI-PEG) denoted as CA-PLGA-b-(PEI-PEG) were synthesized and characterized. CA-PLGA-b-(PEI-PEG) presented low cytotoxicity by MTT and cck-8 assay. The cationic CA-PLGA-b-(PEI-PEG) micelles (diameter about 100 nm and zeta potential 34-61 mV) were prepared through self-assembly method, and complexed with insulin via electrostatic interaction to obtain nanoscale micelle/insulin complexes. The micelle/insulin complexes-loaded CA-PLGA microspheres (MIC-MS, 10.4 ± 3.85 μm) were manufactured by employing a double emulsion (W₁/O/W₂) method. The in vitro insulin release behavior and in vivo hypoglycaemic effect of MIC-MS on streptozotocin (STZ) induced diabetic rats were compared with those of the insulin-loaded CA-PLGA microspheres (INS-MS, 7.8 ± 2.57 μm). The initial burst in vitro release of MIC-MS was markedly lower than that of INS-MS (P < 0.01), and the pharmacological availability of MIC-MS via subcutaneous administration was 148.9% relative to INS-MS. Therefore, the cationic CA-PLGA-b-(PEI-PEG) micelles can effectively increase the bioavailability of insulin in CA-PLGA microspheres and can be considered as a potential protein carrier.

Immune Correlate-Guided HIV Vaccine Design

Although vaccines have been successfully developed against several pathogens, designing an effective vaccine to protect against human immunodeficiency virus (HIV) has remained an intractable challenge. To address this, the research community has looked to human and non-human primate studies to understand the correlates of protective immunity, based on which a targeted vaccine strategy may be designed. Two distinct approaches, focused on different immune correlates of protection, have emerged. The first focuses on structure-based design of HIV envelope immunogens that are able to induce antibodies that neutralize the virus. The second focuses on strategies aimed at driving non-neutralizing polyclonal and polyfunctional antibodies that engage other arms of immunity to clear the virus. Here we review these two different vaccine design strategies and posit that ultimately the convergence of these two efforts will likely be necessary for the development of a globally protective HIV vaccine.

Electrospun Hydrophilic Janus Nanocomposites for the Rapid Onset of Therapeutic Action of Helicid

The oral delivery of active ingredients for the fast onset of therapeutic effects is a well-known method in patients. In this study, a new kind of hydrophilic Janus structural nanocomposite was designed for the rapid dissolution and transmembrane permeation of helicid, an herbal medicine with poor water solubility. A side-by-side electrospinning process characterized by an eccentric spinneret was developed to fabricate the Janus nanocomposites. The morphology, inner structure, incorporated components and their physical states, hydrophilicity, and functional performances of the Janus nanocomposites were investigated. The experimental results demonstrated that an unspinnable fluid (polyvinylpyrrolidone K10-sodium dodecyl sulfate) could be simultaneously treated with an electrospinnable fluid (polyvinylpyrrolidone K90-helicid) to create Janus structural nanocomposites. The prepared Janus nanofibers exhibited linear morphology and notable side-by-side inner structure with all the incorporated components present in an amorphous state. Both the control of monolithic nanocomposites and the Janus composites can provide more than 10-fold the transmembrane rates of crude helicid particles. Compared with monolithic nanocomposites, the Janus nanocomposites exhibited improved hydrophilicity and can further promote the dissolution and transmembrane permeation of helicid for a potentially faster onset of therapeutic actions. The generation mechanisms and functional performance of Janus nanocomposites were suggested. The preparation protocols reported here can provide a useful approach for designing and developing new functional nanocomposites in the form of Janus structures. Meanwhile, the medicated hydrophilic Janus nanocomposites represent a newly developed kind of nano drug delivery system for the fast onset of therapeutic action of orally administered water-insoluble drugs.