Mannose derivative and lipid A dually decorated cationic liposomes as an effective cold chain free oral mucosal vaccine adjuvant-delivery system

Unravelling the in vivo dynamics of liposomes: Insights into biodistribution and cellular membrane interactions

Liposomes, as a colloidal drug delivery system dating back to the 1960s, remain a focal point of extensive research and stand as a highly efficient drug delivery method. The amalgamation of technological and biological advancements has propelled their evolution, elevating them to their current status. The key attributes of biodegradability and biocompatibility have been instrumental in driving substantial progress in liposome development. Demonstrating a remarkable ability to surmount barriers in drug absorption, enhance stability, and achieve targeted distribution within the body, liposomes have become pivotal in pharmaceutical research. In this comprehensive review, we delve into the intricate details of liposomal drug delivery systems, focusing specifically on their pharmacokinetics and cell membrane interactions via fusion, lipid exchange, endocytosis etc. Emphasizing the nuanced impact of various liposomal characteristics, we explore factors such as lipid composition, particle size, surface modifications, charge, dosage, and administration routes. By dissecting the multifaceted interactions between liposomes and biological barriers, including the reticuloendothelial system (RES), opsonization, enhanced permeability and retention (EPR) effect, ATP-binding cassette (ABC) phenomenon, and Complement Activation-Related Pseudoallergy (CARPA) effect, we provide a deeper understanding of liposomal behaviour in vivo. Furthermore, this review addresses the intricate challenges associated with translating liposomal technology into practical applications, offering insights into overcoming these hurdles. Additionally, we provide a comprehensive analysis of the clinical adoption and patent landscape of liposomes across diverse biomedical domains, shedding light on their potential implications for future research and therapeutic developments.

Understanding Mucosal Physiology and Rationale of Formulation Design for Improved Mucosal Immunity

The oral and nasal cavities serve as critical gateways for infectious pathogens, with microorganisms primarily gaining entry through these routes. Our first line of defense against these invaders is the mucosal membrane, a protective barrier that shields the body's internal systems from infection while also contributing to vital functions like air and nutrient intake. One of the key features of this mucosal barrier is its ability to protect the physiological system from pathogens. Additionally, mucosal tolerance plays a crucial role in maintaining homeostasis by regulating the pH and water balance within the body. Recognizing the importance of the mucosal barrier, researchers have developed various mucosal formulations to enhance the immune response. Mucosal vaccines, for example, deliver antigens directly to mucosal tissues, triggering local immune stimulation and ultimately inducing systemic immunity. Studies have shown that lipid-based formulations such as liposomes and virosomes can effectively elicit both local and systemic immune responses. Furthermore, mucoadhesive polymeric particles, with their prolonged delivery to target sites, have demonstrated an enhanced immune response. This Review delves into the critical role of material selection and delivery approaches in optimizing mucosal immunity.

Nanotechnology in the Diagnosis and Treatment of Antibiotic-Resistant Infections

The development of antimicrobial resistance (AMR), along with the relative reduction in the production of new antimicrobials, significantly limits the therapeutic options in infectious diseases. Thus, novel treatments, especially in the current era, where AMR is increasing, are urgently needed. There are several ongoing studies on non-classical therapies for infectious diseases, such as bacteriophages, antimicrobial peptides, and nanotechnology, among others. Nanomaterials involve materials on the nanoscale that could be used in the diagnosis, treatment, and prevention of infectious diseases. This review provides an overview of the applications of nanotechnology in the diagnosis and treatment of infectious diseases from a clinician's perspective, with a focus on pathogens with AMR. Applications of nanomaterials in diagnosis, by taking advantage of their electrochemical, optic, magnetic, and fluorescent properties, are described. Moreover, the potential of metallic or organic nanoparticles (NPs) in the treatment of infections is also addressed. Finally, the potential use of NPs in the development of safe and efficient vaccines is also reviewed. Further studies are needed to prove the safety and efficacy of NPs that would facilitate their approval by regulatory authorities for clinical use.

A Comprehensive review on Pharmacokinetic Studies of Vaccines: Impact of delivery route, carrier-and its modulation on immune response

The lack of knowledge about the absorption, distribution, metabolism, and excretion (ADME) of vaccines makes former biopharmaceutical optimization difficult. This was shown during the COVID-19 immunization campaign, where gradual booster doses were introduced.. Thus, understanding vaccine ADME and its effects on immunization effectiveness could result in a more logical vaccine design in terms of formulation, method of administration, and dosing regimens. Herein, we will cover the information available on vaccine pharmacokinetics, impacts of delivery routes and carriers on ADME, utilization and efficiency of nanoparticulate delivery vehicles, impact of dose level and dosing schedule on the therapeutic efficacy of vaccines, intracellular and endosomal trafficking and in vivo fate, perspective on DNA and mRNA vaccines, new generation sequencing and mathematical models to improve cancer vaccination and pharmacology, and the reported toxicological study of COVID-19 vaccines. Altogether, this review will enhance the reader's understanding of the pharmacokinetics of vaccines and methods that can be implied in delivery vehicle design to improve the absorption and distribution of immunizing agents and estimate the appropriate dose to achieve better immunogenic responses and prevent toxicities.

Liposome-based vaccines for minimally or noninvasive administration: an update on current advancements

INTRODUCTION

Vaccination requires innovation to provide effective protection. Traditional vaccines have several drawbacks, which can be overcome with advanced technologies and different administration routes. Over the past 10  years, a significant amount of research has focussed on the delivery of antigens into liposomes due to their dual role as antigen-carrying systems and vaccine adjuvants able to increase the immunogenicity of the carried antigen.

AREAS COVERED

This review encompasses the progress made over the last 10  years with liposome-based vaccines designed for minimally or noninvasive administration, filling the gaps in previous reviews and providing insights on composition, administration routes, results achieved, and Technology Readiness Level of the most recent formulations.

EXPERT OPINION

Liposome-based vaccines administered through minimally or noninvasive routes are expected to improve efficacy and complacency of vaccination programs. However, the translation from lab-scale production to large-scale production and collaborations with hospitals, research centers, and companies are needed to allow new products to enter the market and improve the vaccination programs in the future.

Mucoadhesive Vaccine Delivery Systems for the Oral Mucosa

Vaccine technology has evolved continuously since its beginning, and mucosal vaccination, including intranasal, sublingual, and oral administrations, has recently gained great scientific interest. The oral mucosa represents a promising minimally invasive route for antigen delivery, mainly at sublingual and buccal mucosal sites, and it is easily accessible, immunologically rich, and able to promote an effective systemic and local immune response. The aim of this review is to provide an updated overview on the technologies for oral mucosal vaccination, with emphasis on mucoadhesive biomaterial-based delivery systems. Polymeric-based nanoparticles, multilayer films and wafers, liposomes, microneedles, and thermoresponsive gels are the most investigated strategies to deliver antigens locally, showing mucoadhesive properties, controlled release of the antigen, and the ability to enhance immunological responses. These formulations have achieved adequate properties in terms of vaccine stability, are minimally invasive, and are easy to produce and manage. To date, oral mucosa vaccine delivery systems represent a promising and open field of research. Future directions should focus on the role of these systems to induce sustained innate and adaptive immune responses, by integrating the recent advances achieved in mucoadhesion with those related to vaccine technology. Being painless, easy to administer, highly stable, safe, and effective, the antigen delivery systems via the oral mucosa may represent a useful and promising strategy for fast mass vaccination, especially during pandemic outbreaks.

Buccal delivery of small molecules and biologics: Of mucoadhesive polymers, films, and nanoparticles - An update

Buccal delivery of small and large molecules is an attractive route of administration that has been studied extensively over the past few decades. This route bypasses first-pass metabolism and can be used to deliver therapeutics directly to systemic circulation. Moreover, buccal films are efficient dosage forms for drug delivery due to their simplicity, portability, and patient comfort. Films have traditionally been formulated using conventional techniques, including hot-melt extrusion and solvent casting. However, newer methods are now being exploited to improve the delivery of small molecules and biologics. This review discusses recent advances in buccal film manufacturing, using the latest technologies, such as 2D and 3D printing, electrospraying, and electrospinning. This review also focuses on the excipients used in the preparation of these films, with emphasis on mucoadhesive polymers and plasticizers. Along with advances in manufacturing technology, newer analytical tools have also been used for the assessment of permeation of the active agents across the buccal mucosa, the most critical biological barrier and limiting factor of this route. Additionally, preclinical and clinical trial challenges are discussed, and some small molecule products already on the market are explored.

Oromucosal delivery of macromolecules: Challenges and recent developments to improve bioavailability

Owing to their biological diversity, high potency, good tolerability, low immunogenicity, site-specific activity, and great efficacy, macromolecular drugs (i.e., proteins and peptides, antibodies, hormones, nucleic acids, vaccines, etc.) are extensively used as diagnostics, prophylactics, and therapeutics in various diseases. To overcome drawbacks associated with parenteral (invasive) delivery of macromolecules as well as to preserve their therapeutic integrity, oromucosal route (sublingual and buccal) has been proven efficient alternate port of delivery. This review aims to summarize challenges associated with oromucosal route and overtime developments in conventional delivery systems with special emphasis on most recent delivery strategies. Over the past few decades, significant efforts have been made for improving the oromucosal absorption of macromolecules by employing chemical penetration enhancers (CPE), enzyme inhibitors, chemical modification of drug structure (i.e., lipidation, PEGylation, etc.), and mucoadhesive materials in the form of buccal tablets, films (or patches), sprays, fast disintegrating tablets, and microneedles. Adaptation of adjunct strategies (e.g., iontophoresis in conjunction with CPE) has shown significant improvement in oromucosal absorption of macromolecules; however, these approaches were also associated with many drawbacks. To overcome these shortcomings and to further improve therapeutic outcomes, specialized delivery devices called "hybrid nanosystems" have been designed in recent times. This newer intervention showed promising potential for promoting oromucosal absorption and absolute bioavailability of macromolecules along with improved thermostability (cold chain free storage), enabling self-administration, site-specific activity, improving therapeutic efficacy and patient compliance. We anticipate that tailoring of hybrid nanosystems to clinical trials as well as establishing their short- and long-term safety profile would substantiate their therapeutic value as pharmaceutical devices for oromucosal delivery of macromolecules.

Applications of mannose-binding lectins and mannan glycoconjugates in nanomedicine

Glycosylated nanoparticles (NPs) have drawn a lot of attention in the biomedical field over the past few decades, particularly in applications like targeted drug delivery. Mannosylated NPs and mannan-binding lectins/proteins (MBL/MBP) are emerging as promising tools for delivery of drugs, medicines, and enzymes to targeted tissues and cells as nanocarriers, enhancing their therapeutic benefits while avoiding the adverse effects of the drug. The occurrence of plenty of lectin receptors and their mannan ligands on cell surfaces makes them multifaceted carriers appropriate for specific delivery of bioactive drug materials to their targeted sites. Thus, the present review describes the tethering of mannose (Man) to several nanostructures, like micelles, liposomes, and other NPs, applicable for drug delivery systems. Bioadhesion through MBL-like receptors on cells has involvements applicable to additional arenas of science, for example gene delivery, tissue engineering, biomaterials, and nanotechnology. This review also focuses on the role of various aspects of drug/antigen delivery using (i) mannosylated NPs, (ii) mannosylated lectins, (iii) amphiphilic glycopolymer NPs, and (iv) natural mannan-containing polysaccharides, with most significant applications of MBL-based NPs as multivalent scaffolds, using different strategies.

GRAPHICAL ABSTRACT

Mannosylated NPs and/or MBL/MBP are coming up as viable and versatile tools as nanocarriers to deliver drugs and enzymes precisely to their target tissues or cells. The presence of abundant number of lectin receptors and their mannan ligands on cell surfaces makes them versatile carriers suitable for the targeted delivery of bioactive drugs.

Nanovesicles-Mediated Drug Delivery for Oral Bioavailability Enhancement

Bioavailability is an eternal topic that cannot be circumvented by peroral drug delivery. Adequate blood drug exposure after oral administration is a prerequisite for effective treatment. Nanovesicles as pleiotropic oral vehicles can solubilize, encapsulate, stabilize an active ingredient and promote the payload absorption via various mechanisms. Vesicular systems with nanoscale size, such as liposomes, niosomes and polymersomes, provide a versatile platform for oral delivery of drugs with distinct nature. The amphiphilicity of vesicles in structure allows hydrophilic and lipophilic molecule(s) either or both to be loaded, being encapsulated in the aqueous cavity or the inner core, respectively. Depending on high oral transport efficiency based on their structural flexibility, gastrointestinal stability, biocompatibility, and/or intestinal epithelial affinity, nanovesicles can markedly augment the oral bioavailability of various poorly absorbed drugs. Vesicular drug delivery systems (VDDSs) demonstrate a lot of preferences and are becoming more prominent of late years in biomedical applications. Equally, these systems can potentiate a drug's therapeutic index by ameliorating the oral absorption. This review devotes to comment on various VDDSs with special emphasis on the peroral drug delivery. The classification of nanovesicles, preparative processes, intestinal transport mechanisms, in vivo fate, and design rationale were expounded. Knowledge on vesicles-mediated oral drug delivery for bioavailability enhancement has been properly provided. It can be concluded that VDDSs with many merits will step into an energetic arena in oral drug delivery.

Development of Nasal Vaccines and the Associated Challenges

Viruses, bacteria, fungi, and several other pathogenic microorganisms usually infect the host via the surface cells of respiratory mucosa. Nasal vaccination could provide a strong mucosal and systemic immunity to combat these infections. The intranasal route of vaccination offers the advantage of easy accessibility over the injection administration. Therefore, nasal immunization is considered a promising strategy for disease prevention, particularly in the case of infectious diseases of the respiratory system. The development of a nasal vaccine, particularly the strategies of adjuvant and antigens design and optimization, enabling rapid induction of protective mucosal and systemic responses against the disease. In recent times, the development of efficacious nasal vaccines with an adequate safety profile has progressed rapidly, with effective handling and overcoming of the challenges encountered during the process. In this context, the present report summarizes the most recent findings regarding the strategies used for developing nasal vaccines as an efficient alternative to conventional vaccines.

Mucosal vaccine delivery: A focus on the breakthrough of specific barriers

Mucosal vaccines can effectively induce an immune response at the mucosal site and form the first line of defense against microbial invasion. The induced mucosal immunity includes the proliferation of effector T cells and the production of IgG and IgA antibodies, thereby effectively blocking microbial infection and transmission. However, after a long period of development, the transformation of mucosal vaccines into clinical use is still relatively slow. To date, fewer than ten mucosal vaccines have been approved. Only seven mucosal vaccines against coronavirus disease 2019 (COVID-19) are under investigation in clinical trials. A representative vaccine is the adenovirus type-5 vectored COVID-19 vaccine (Ad5-nCoV) developed by Chen and coworkers, which is currently in phase III clinical trials. The reason for the limited progress of mucosal vaccines may be the complicated mucosal barriers. Therefore, this review summarizes the characteristics of mucosal barriers and highlights strategies to overcome these barriers for effective mucosal vaccine delivery.

Mucosal immunity of mannose-modified chitosan microspheres loaded with the nontyepable Haemophilus influenzae outer membrane protein P6 in BALB/c mice

Nontypeable Haemophilus influenzae (NTHi) is a common opportunistic pathogen that colonizes the nasopharynx. NTHi infections result in enormous global morbidity in two clinical settings: otitis media in children and acute exacerbation of chronic obstructive pulmonary disease (COPD) in adults. Thus, there is an urgent need to design and develop effective vaccines to prevent morbidity and reduce antibiotic use. The NTHi outer membrane protein P6, a potential vaccine candidate, is highly conserved and effectively induces protective immunity. Here, to enhance mucosal immune responses, P6-loaded mannose-modified chitosan (MC) microspheres (P6-MCMs) were developed for mucosal delivery. MC (18.75%) was synthesized by the reductive amination reaction method using sodium cyanoborohydride (NaBH₃CN), and P6-MCMs with an average size of 590.4±16.2 nm were successfully prepared via the tripolyphosphate (TPP) ionotropic gelation process. After intranasal immunization with P6-MCMs, evaluation of humoral immune responses indicated that P6-MCMs enhance both systemic and mucosal immune responses. Evaluation of cellular immune responses indicated that P6-MCMs enhance cellular immunity and trigger a mixed Th1/Th2-type immune response. Importantly, P6-MCMs also trigger a Th17-type immune response. They are effective in promoting lymphocyte proliferation and differentiation without toxicity in vitro. The results also demonstrate that P6-MCMs can effectively induce MHC class I- and II-restricted cross-presentation, promoting CD4⁺-mediated Th immune responses and CD8⁺-mediated cytotoxic T lymphocyte (CTL) immune responses. Evaluation of protective immunity indicated that immunization with P6-MCMs can reduce inflammation in the nasal mucosa and the lung and prevent NTHi infection. In conclusion, MCMs are a promising adjuvant-delivery system for vaccines against NTHi.

Development of Peptide-Based Vaccines for Cancer

Peptides cancer vaccines are designed based on the epitope peptides that can elicit humoral and cellular immune responses targeting tumor-associated antigens (TAAs) or tumor-specific antigens (TSAs). In order to develop a clinically safe and more effective vaccine for the future, several issues need to be addressed, and these include the selection of optimal antigen targets, adjuvants, and immunization regimens. Another emerging approach involves the use of personalized peptide-based vaccines based on neoantigens to enhance antitumor response. Rationally designed combinatorial therapy is currently being investigated with chemotherapeutic drugs or immune checkpoint inhibitor therapies to improve the efficacy. This review discusses an overview of the development of peptide-based vaccines, the role of adjuvants, and the delivery systems for peptide vaccines as well as combinatorial therapy as potential anticancer strategies.

Current view on novel vaccine technologies to combat human infectious diseases

Inactivated and live attenuated vaccines have improved human life and significantly reduced morbidity and mortality of several human infectious diseases. However, these vaccines have faults, such as reactivity or suboptimal efficacy and expensive and time-consuming development and production. Additionally, despite the enormous efforts to develop vaccines against some infectious diseases, the traditional technologies have not been successful in achieving this. At the same time, the concerns about emerging and re-emerging diseases urge the need to develop technologies that can be rapidly applied to combat the new challenges. Within the last two decades, the research of vaccine technologies has taken several directions to achieve safe, efficient, and economic platforms or technologies for novel vaccines. This review will give a brief overview of the current state of the novel vaccine technologies, new vaccine candidates in clinical trial phases 1-3 (listed by European Medicines Agency (EMA) and Food and Drug Administration (FDA)), and vaccines based on the novel technologies which have already been commercially available (approved by EMA and FDA) with the special reference to pandemic COVID-19 vaccines. KEY POINTS: • Vaccines of the new generation follow the minimalist strategy. • Some infectious diseases remain a challenge for the vaccine development. • The number of new vaccine candidates in the late phase clinical trials remains low.

Oral delivery of proteins and peptides: Challenges, status quo and future perspectives

Proteins and peptides (PPs) have gradually become more attractive therapeutic molecules than small molecular drugs due to their high selectivity and efficacy, but fewer side effects. Owing to the poor stability and limited permeability through gastrointestinal (GI) tract and epithelia, the therapeutic PPs are usually administered by parenteral route. Given the big demand for oral administration in clinical use, a variety of researches focused on developing new technologies to overcome GI barriers of PPs, such as enteric coating, enzyme inhibitors, permeation enhancers, nanoparticles, as well as intestinal microdevices. Some new technologies have been developed under clinical trials and even on the market. This review summarizes the history, the physiological barriers and the overcoming approaches, current clinical and preclinical technologies, and future prospects of oral delivery of PPs.

Overcoming barriers by local drug delivery with liposomes

Localized or topical administration of drugs may be considered as a potential approach for overcoming the problems caused by the various biological barriers encountered in drug delivery. The combination of using localized administration routes and delivering drugs in nanoparticulate formulations, such as liposomes, may have additional advantages. Such advantages include prolonged retention of high drug loads at the site of action and controlled release of the drug, ensuring prolonged therapeutic effect; decreased potential for side-effects and toxicity (due to the high topical concentrations of drugs); and increased protection of drugs from possible harsh environments at the site of action. The use of targeted liposomal formulations may further potentiate any acquired therapeutic advantages. In this review we present the most advanced cases of localized delivery of liposomal formulations of drugs, which have been investigated pre-clinically and clinically in the last ten years, together with the reported therapeutic advantages, in each case.

Beyond Just Peptide Antigens: The Complex World of Peptide-Based Cancer Vaccines

Peptide-based cancer vaccines rely upon the strong activation of the adaptive immune response to elicit its effector function. They have shown to be highly specific and safe, but have yet to prove themselves as an efficacious treatment for cancer in the clinic. This is for a variety of reasons, including tumour heterogeneity, self-tolerance, and immune suppression. Importance has been placed on the overall design of peptide-based cancer vaccines, which have evolved from simple peptide derivatives of a cancer antigen, to complex drugs; incorporating overlapping regions, conjugates, and delivery systems to target and stimulate different components of antigen presenting cells, and to bolster antigen cross-presentation. Peptide-based cancer vaccines are increasingly becoming more personalised to an individual's tumour antigen repertoire and are often combined with existing cancer treatments. This strategy ultimately aids in combating the shortcomings of a more generalised vaccine strategy and provides a comprehensive treatment, taking into consideration cancer cell variability and its ability to avoid immune interrogation.

Recent advances in nano/microparticle-based oral vaccines

Background

Vaccines are often recognized as one of the most cost-effective public health interventions in controlling infectious diseases. Most pathogens infiltrate the body from mucosal sites, primarily from the oral and pulmonary region and reach the systemic circulation where disease manifestation starts. Traditional needle-based vaccines are usually not capable of inducing immunity at the mucosal sites where pathogen infiltrates start, but induces systemic immunity. In contrast to needle-based vaccines, mucosally administered vaccines induce immunity at both the mucosal sites and systemically. The oral route of immunization is the most convenient way to administer the vaccines. However, due to the complicated and hostile gastrointestinal structure and environment, vaccines need to overcome major hurdles while retaining their stability and immunogenicity.

Area covered

This review will briefly discuss different barriers to oral vaccine development. It gives a brief overview of different types of nano/microparticle-based oral vaccines and discusses how physicochemical characteristics of the particles influence overall immunity after oral immunization.

Expert opinion

Formulation strategies using novel lipid and polymer-based nano/microparticle platforms retain stability and antigenicity of vaccines against the harsh gastrointestinal condition. The physicochemical properties of particles can be uniquely tailored to prolong the release of antigens, and attached ligands (M-cells and APC-ligands) can precisely target uptake by immune cells. These represent viable strategies for efficient delivery of oral vaccines.

Development of thermostable vaccine adjuvants

INTRODUCTION

The importance of vaccine thermostability has been discussed in the literature. Nevertheless, the challenge of developing thermostable vaccine adjuvants has sometimes not received appropriate emphasis. Adjuvants comprise an expansive range of particulate and molecular compositions, requiring innovative thermostable formulation and process development approaches.

AREAS COVERED

Reports on efforts to develop thermostable adjuvant-containing vaccines have increased in recent years, and substantial progress has been made in enhancing the stability of the major classes of adjuvants. This narrative review summarizes the current status of thermostable vaccine adjuvant development and looks forward to the next potential developments in the field.

EXPERT OPINION

As adjuvant-containing vaccines become more widely used, the unique challenges associated with developing thermostable adjuvant formulations merit increased attention. In particular, more focused efforts are needed to translate promising proof-of-concept technologies and formulations into clinical products.

The sixth revolution in pediatric vaccinology: immunoengineering and delivery systems

Infection is the predominant cause of mortality in early life, and immunization is the most promising biomedical intervention to reduce this burden. However, very young infants fail to respond optimally to most vaccines currently in use, especially neonates. In 2005, Stanley Plotkin proposed that new delivery systems would spur a new revolution in pediatric vaccinology, just as attenuation, inactivation, cell culture of viruses, genetic engineering, and adjuvantation had done in preceding decades. Recent advances in the field of immunoengineering, which is evolving alongside vaccinology, have begun to increasingly influence vaccine formulation design. Historically, the particulate nature of materials used in many vaccine formulations was empiric, often because of the need to stabilize antigens or reduce endotoxin levels. However, present vaccine delivery systems are rationally engineered to mimic the size, shape, and surface chemistry of pathogens, and are therefore often referred to as "pathogen-like particles". More than a decade from his original assessment, we re-assess Plotkin's prediction. In addition, we highlight how immunoengineering and advanced delivery systems may be uniquely capable of enhancing vaccine responses in vulnerable populations, such as infants. IMPACT: Immunoengineering and advanced delivery systems are leading to new developments in pediatric vaccinology. Summarizes delivery systems currently in use and development, and prospects for the future. Broad overview of immunoengineering's impact on vaccinology, catering to Pediatric Clinicians and Immunologists.

Aluminum Nanoparticles Acting as a Pulmonary Vaccine Adjuvant-Delivery System (VADS) Able to Safely Elicit Robust Systemic and Mucosal Immunity

Abstract

Vulnerability of respiratory mucosa to invasions of airborne pathogens, such as SARS-CoV, MERS-CoV and avian viruses which sometimes cause a life-threatening epidemic and even pandemic, underscores significance of developing a pulmonary vaccine adjuvant-delivery system (VADS). Herein, 30-nm aluminum nanoparticles (ANs), unlike the mostly used adjuvant alum which is unsuitable for delivering pulmonary vaccines due to side effects, proved able to act as a VADS fitting inhalation immunization to elicit wide-spread anti-antigen immunity. In vitro ANs facilitated cellular uptake of their cargos and, after pulmonary vaccination, induced mouse production of high levels of anti-antigen IgG in serum and IgA in saliva, nasal, bronchoalveolar and also vaginal fluids. Besides, IFN-γ and anti-antigen IgG2a enriched in immunized mice which meanwhile showed no obvious lung inflammation indicated balanced Th1/Th2 responses were safely induced. These outcomes suggest ANs may be an efficient pulmonary VADS for defending against pathogens, especially, the ones invading hosts via respiratory system.

Graphic Abstract

Aluminum nanoparticles can safely induce humoral and cellular immunity at systemic and mucosal level through pulmonary vaccination to contrast the conventional adjuvant alum.

Nanoparticles for mucosal vaccine delivery

Mucosal surfaces represent important routes of entry into the human body for the majority of pathogens, and they constitute unique sites for targeted vaccine delivery. Nanoparticle-based drug delivery systems are emerging technologies for delivering and improving the efficacy of mucosal vaccines. Recent studies have provided new insights into formulation and delivery aspects of importance for the design of safe and efficacious mucosal subunit vaccines based on nanoparticles. These include novel nanomaterials, their physicochemical properties and formulation approaches, nanoparticle interaction with immune cells in the mucosa, and mucosal immunization and delivery strategies. Here, we present recent progress in the application of nanoparticle-based approaches for mucosal vaccine delivery and discuss future research challenges and opportunities in the field.

An overview of biodegradable nanomaterials and applications in vaccines

Vaccination is the most cost-effective and sustainable way to prevent and eliminate infectious diseases. Compared with traditional vaccines, novel vaccines have better stability, longer duration and require less antigen usage. In addition, novel vaccines have better immune effects and significantly less toxic side effects. However, both novel vaccines and traditional vaccines require carrier molecules or adjuvants to produce an optimal immune response. There is an increasing demand for vaccine adjuvants and delivery systems that can induce stronger immune response whilst reducing production cost and the dose of vaccine. In recent years, nanotechnology has played an important role in the development of novel vaccine adjuvants and nano-delivery systems. Biodegradable materials have also received a lot of attention in medical science because they have excellent biocompatibility, biodegradability and low toxicity, which can protect antigens from degradation, increase antigen stability and provide slow release; resulting in enhanced immunogenicity. Therefore, biodegradable nanoparticles have attracted much attention in the formulation of vaccines. In this review, we outline some key features of biodegradable nanomaterials in the developing safer and more effective vaccines. The properties, structural characteristics, advantages and disadvantage of the biodegradable nanomaterials will be systematically reviewed. Additionally, applications, research progress and future prospects of biodegradable nanomaterials are discussed. This review will be help in future research work directed at developing biodegradable vaccine adjuvants or delivery carriers.

Covering Aluminum Oxide Nanoparticles with Biocompatible Materials to Efficiently Deliver Subunit Vaccines

Subunit vaccines have advantages of good safety, minimal reactogenicity, and high specificity. However, subunit vaccines also show a crucial disadvantage of poor immunogenicity and, therefore, are often formulated with an adjuvant carrier to form a vaccine adjuvant-delivery system (VADS) to enhance their efficacies. Alums, the coarse aggregates of the insoluble aluminum salts, are the conventional adjuvants and have been widely used in clinical vaccines for a long time. Unfortunately, alums also show two main drawbacks of low potency in eliciting cellular immunity, and high reactogenicity to cause unwanted inflammations. Therefore, herein the phospholipid bilayer-coated aluminum oxide nanoparticles (PLANs) and the PEGylated PLANs (PEG-PLANs) were engineered as a VADS to overcome the drawbacks of both subunit vaccines and coarse alums, while synergizing their functions. In vitro experiments demonstrated that, unlike the micron-sized alums, the nanosized PLANs and PEG-PLANs loaded with model antigen of ovalbumin (OVA) showed a high safety profile and were able to promote APC (antigen-presenting cell) uptake and engender lysosome escape for enhancing the MHC (major histocompatibility complex)-I-antigen display. Subcutaneously administered to mice, PLANs and, especially, PEG-PLANs smoothly trafficked into the draining lymph nodes, wherein the densely clustered immune cells were activated in substantial numbers, leading to robust immunoresponses and efficient production of the anti-antigen antibodies and CD8+ T cells. Thus, the aluminum-based nanocarriers, especially the PEG-PLANs, are a promising VADS possessing the potential of eliciting strong and comprehensive immunity against pathogens.

Liposomes used as a vaccine adjuvant-delivery system: From basics to clinical immunization

Liposomes are widely utilized as a carrier to improve therapeutic efficacy of agents thanks to their merits of high loading capacity, targeting delivery, reliable protection of agents, good biocompatibility, versatile structure modification and adjustable characteristics, such as size, surface charge, membrane flexibility and the agent loading mode. In particular, in recent years, through modification with immunopotentiators and targeting molecules, and in combination with innovative immunization devices, liposomes are rapidly developed as a multifunctional vaccine adjuvant-delivery system (VADS) that has a high capability in inducing desired immunoresponses, as they can target immune cells and even cellular organelles, engender lysosome escape, and promote Ag cross-presentation, thus enormously enhancing vaccination efficacy. Moreover, after decades of development, several products developed on liposome VADS have already been authorized for clinical immunization and are showing great advantages over conventional vaccines. This article describes in depth some critical issues relevant to the development of liposomes as a VADS, including principles underlying immunization, physicochemical properties of liposomes as the immunity-influencing factors, functional material modification to enhance immunostimulatory functions, the state-of-the-art liposome VADSs, as well as the marketed vaccines based on a liposome VADS. Therefore, this article provides a comprehensive reference to the development of novel liposome vaccines.

Adapting liposomes for oral drug delivery

Liposomes mimic natural cell membranes and have long been investigated as drug carriers due to excellent entrapment capacity, biocompatibility and safety. Despite the success of parenteral liposomes, oral delivery of liposomes is impeded by various barriers such as instability in the gastrointestinal tract, difficulties in crossing biomembranes, and mass production problems. By modulating the compositions of the lipid bilayers and adding polymers or ligands, both the stability and permeability of liposomes can be greatly improved for oral drug delivery. This review provides an overview of the challenges and current approaches toward the oral delivery of liposomes.

Novel imiquimod nanovesicles for topical vaccination

Development of needle and pain free noninvasive immunization procedures is a top priority for public health agencies. In this work the topical adjuvant activity of the immunomodulator imiquimod (IMQ) carried by ultradeformable archaeosomes (UDA₂) (nanovesicles containing sn-2,3 ether linked phytanyl saturated archaeolipids) was surveyed and compared with that of ultradeformable liposomes lacking archaeolipids (UDL₂) and free IMQ, using the model antigen ovalbumin and a seasonal influenza vaccine in Balb/c mice. UDA₂ (250 ± 94 nm, -26 ± 4 mV Z potential) induced higher IMQ accumulation in human skin and higher production of TNF-α and IL-6 by macrophages and keratinocytes than free IMQ and UDL₂. Mixed with ovalbumin, UDA₂ was more efficient at generating cellular response, as measured by an increase in serum IgG2a and INF-γ production by splenocytes, compared with free IMQ and UDL₂. Moreover, mixed with a seasonal influenza vaccine UDA₂ produced same IgG titers and IgG2a/IgG1 isotypes ratio (≈1) than the subcutaneously administered influenza vaccine. Topical UDA₂ however, induced highest stimulation index and INF-γ levels by splenocytes. UDA₂ might be a promising adjuvant for topical immunization, since it produced cell-biased systemic response with ≈ 13-fold lower IMQ dose than the delivered as the commercial IMQ cream, Aldara.

Optimization of the Linker Length of Mannose-Cholesterol Conjugates for Enhanced mRNA Delivery to Dendritic Cells by Liposomes

Liposomes (LPs) as commonly used mRNA delivery systems remain to be rationally designed and optimized to ameliorate the antigen expression of mRNA vaccine in dendritic cells (DCs). In this study, we synthesized mannose-cholesterol conjugates (MP_n-CHs) by click reaction using different PEG units (PEG₁₀₀, PEG₁₀₀₀, and PEG₂₀₀₀) as linker molecules. MP_n-CHs were fully characterized and subsequently used to prepare DC-targeting liposomes (MP_n-LPs) by a thin-film dispersion method. MP_n-LPs loaded with mRNA (MP_n-LPX) were finally prepared by a simple self-assembly method. MP_n-LPX displayed bigger diameter (about 135 nm) and lower zeta potential (about 40 mV) compared to MP_n-LPs. The in vitro transfection experiment on DC2.4 cells demonstrated that the PEG length of mannose derivatives had significant effect on the expression of GFP-encoding mRNA. MP₁₀₀₀-LPX containing MP₁₀₀₀-CH can achieve the highest transfection efficiency (52.09 ± 4.85%), which was significantly superior to the commercial transfection reagent Lipo 3K (11.47 ± 2.31%). The optimal DC-targeting MP₁₀₀₀-LPX showed an average size of 132.93 ± 4.93 nm and zeta potential of 37.93 ± 2.95 mV with nearly spherical shape. Moreover, MP₁₀₀₀-LPX can protect mRNA against degradation in serum with high efficacy. The uptake study indicated that MP₁₀₀₀-LPX enhanced mRNA expression mainly through the over-expressing mannose receptor (CD206) on the surface of DCs. In conclusion, mannose modified LPs might be a potential DC-targeting delivery system for mRNA vaccine after rational design and deserve further study on the in vivo delivery profile and anti-tumor efficacy.

Oral Vaccine Delivery for Intestinal Immunity-Biological Basis, Barriers, Delivery System, and M Cell Targeting

Most currently available commercial vaccines are delivered by systemic injection. However, needle-free oral vaccine delivery is currently of great interest for several reasons, including the ability to elicit mucosal immune responses, ease of administration, and the relatively improved safety. This review summarizes the biological basis, various physiological and immunological barriers, current delivery systems with delivery criteria, and suggestions for strategies to enhance the delivery of oral vaccines. In oral vaccine delivery, basic requirements are the protection of antigens from the GI environment, targeting of M cells and activation of the innate immune response. Approaches to address these requirements aim to provide new vaccines and delivery systems that mimic the pathogen's properties, which are capable of eliciting a protective mucosal immune response and a systemic immune response and that make an impact on current oral vaccine development.

Loss of integrity of doxorubicin liposomes during transcellular transportation evidenced by fluorescence resonance energy transfer effect

The aim of this work was to elucidate the influence of liposome characteristics on the transcellular process by in vitro studies that would enable designing more efficient oral formulations. Various liposomes with different properties were prepared, including 100-500 nm, anionic, cationic and PEGylated liposomes. All liposomes were labeled by fluorescence resonance energy transfer (FRET) probes to evaluate their integrity in cellular uptake and transport. The FRET fluorescent intensity is proportional to the amount of intact liposomes, which was used to calculate the amount of intact liposomes in cellular uptake and transport. The liposomal structures were found to lose their integrity during or after uptake and only about 20% intact liposomes were detected in cells. However, more cationic liposomes were transported integrally across cell monolayer and accounted for 40.49% of total transport by triple culture models of Caco-2/HT29-MTX/Raji B. These results suggest that liposomes could improve cellular uptake and transport of the payloads significantly, but only a small fraction of liposomes are transported integrally across epithelial monolayer. The study is therefore helpful to rationally fabricate more efficient oral liposomes for poorly water-soluble drugs or biomacromolecules.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Effect of liposome‑mediated HSP27 transfection on collagen synthesis in alveolar type II epithelial cells

To investigate the effect of liposome Lipofectamine® 2000‑mediated HSP27 plasmid transfection in A549 human alveolar type II epithelial cell line on collagen synthesis during transforming growth factor‑β1 (TGF‑β1)‑induced type II epithelial cell transition to myofibroblasts. Cells were transfected with varying ratios of the Lipofectamine® 2000‑mediated heat shock protein 27 (HSP27) plasmid and the transfection efficiency was determined using flow cytometry. The maximum transfection efficacy was confirmed by laser confocal microscopy. HSP gene expression and the most efficient HSP27 plasmid were determined using reverse transcription‑quantitative polymerase chain reaction. Western blot analysis was used to examine HSP27 and collagen expression levels. With a transfection efficiency of 83%, the 8 µg:20 µl ratio of liposome: Plasmid had the highest transfection levels. Among the four different interference sequences in the HSP27 plasmid, the D sequence had the highest interference effect with 70% silencing of the HSP27 gene. The expression of type I and III collagen in TGF‑β1‑induced transition of A549 human alveolar type II epithelial cell line to myofibroblasts was significantly downregulated by the successful transfection with HSP27‑interfering plasmid. The expression of type I and III collagen in the TGF‑β1‑induced transition of A549 cells to myofibroblasts was significantly downregulated by transfection of A549 cells with HSP27 plasmid D‑interfering sequence and optimal ratio of Lipofectamine® 2000 and HSP27 plasmid.

Lipid-Based Particles: Versatile Delivery Systems for Mucosal Vaccination against Infection

Vaccination is the process of administering immunogenic formulations in order to induce or harness antigen (Ag)-specific antibody and T cell responses in order to protect against infections. Important successes have been obtained in protecting individuals against many deleterious pathological situations after parenteral vaccination. However, one of the major limitations of the current vaccination strategies is the administration route that may not be optimal for the induction of immunity at the site of pathogen entry, i.e., mucosal surfaces. It is now well documented that immune responses along the genital, respiratory, or gastrointestinal tracts have to be elicited locally to ensure efficient trafficking of effector and memory B and T cells to mucosal tissues. Moreover, needle-free mucosal delivery of vaccines is advantageous in terms of safety, compliance, and ease of administration. However, the quest for mucosal vaccines is challenging due to (1) the fact that Ag sampling has to be performed across the epithelium through a relatively limited number of portals of entry; (2) the deleterious acidic and proteolytic environment of the mucosae that affect the stability, integrity, and retention time of the applied Ags; and (3) the tolerogenic environment of mucosae, which requires the addition of adjuvants to elicit efficient effector immune responses. Until now, only few mucosally applicable vaccine formulations have been developed and successfully tested. In animal models and clinical trials, the use of lipidic structures such as liposomes, virosomes, immune stimulating complexes, gas-filled microbubbles and emulsions has proven efficient for the mucosal delivery of associated Ags and the induction of local and systemic immune reponses. Such particles are suitable for mucosal delivery because they protect the associated payload from degradation and deliver concentrated amounts of Ags via specialized sampling cells (microfold cells) within the mucosal epithelium to underlying antigen-presenting cells. The review aims at summarizing recent development in the field of mucosal vaccination using lipid-based particles. The modularity ensured by tailoring the lipidic design and content of particles, and their known safety as already established in humans, make the continuing appraisal of these vaccine candidates a promising development in the field of targeted mucosal vaccination.

Glycyrrhetinic Acid Liposomes Containing Mannose-Diester Lauric Diacid-Cholesterol Conjugate Synthesized by Lipase-Catalytic Acylation for Liver-Specific Delivery

Mannose-diester lauric diacid-cholesterol (Man-DLD-Chol), as a liposomal target ligand, was synthesized by lipase catalyzed in a non-aqueous medium. Its chemical structure was confirmed by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. Glycyrrhetinic acid (GA) liposomes containing Man-DLD-Chol (Man-DLD-Chol-GA-Lp) were prepared by the film-dispersion method. We evaluated the characterizations of liposomes, drug-release in vitro, the hemolytic test, cellular uptake, pharmacokinetics, and the tissue distributions. The cellular uptake in vitro suggested that the uptake of Man-DLD-Chol-modified liposomes was significantly higher than that of unmodified liposomes in HepG2 cells. Pharmacokinetic parameters indicated that Man-DLD-Chol-GA-Lp was eliminated more rapidly than GA-Lp. In tissue distributions, the targeting efficiency (Te) of Man-DLD-Chol-GA-Lp on liver was 54.67%, relative targeting efficiency (R_Te) was 3.39, relative uptake rate (Re) was 4.78, and peak concentration ratio (Ce) was 3.46. All these results supported the hypothesis that Man-DLD-Chol would be an efficient liposomal carrier, and demonstrated that Man-DLD-Chol-GA-Lp has potential as a drug delivery for liver-targeting therapy.

Buccal delivery of small molecules and biologics: of mucoadhesive polymers, films, and nanoparticles

Buccal delivery of macromolecules (biologics) sets a great challenge for researchers. Although several niche small molecule products have been approved as simple sprays, tablets and oral films, it is not simply a case of adapting existing technologies to biologics. Buccal delivery of insulin has reached clinical trials with two approaches: oromucosal sprays of the peptide with permeation enhancers, and embedded gold nanoparticles in a dissolvable film. However, neither of these approaches have led to FDA approvals likely due to poor efficacy, submaximal peptide loading in the dosage form, and to wide intra-subject variability in pharmacokinetics and pharmacodynamics. It is likely however that printed film designs with lower molecular weight stable biotech payloads including lipophilic glucagon-like 1 (GLP-1) agonists and macrocycles with long half-lives will generate greater efficacy than was achieved to date for insulin.

Synthesis and evaluation of L-arabinose-based cationic glycolipids as effective vectors for pDNA and siRNA in vitro

Glycolipids might become a new type of promising non-viral gene delivery systems because of their low cytotoxicity, structural diversity, controllable aqua- and lipo-solubility, appropriate density and distribution of positive charges, high transfer efficiency and potential targeting function. In this study, four kinds of L-arabinose-based cationic glycolipids (Ara-DiC12MA, Ara-DiC14MA, Ara-DiC16MA and Ara-DiC18MA) containing quaternary ammonium as hydrophilic headgroup and two alkane chains as hydrophobic domain were synthesized and characterized. They were observed to have strong affinities for plasmid DNA (pDNA) and siRNA, the pDNA can be completely condensed at N/P ratio less than 2, and the siRNA can be completely retarded at N/P ratio less than 3. The dynamic light scattering (DLS) experiment and atomic force microscopy (AFM) experiment demonstrated that cationic lipids and their lipoplexes possessed suitable particle sizes with near-spherical shape and proper ζ-potentials for cell transfection. The Ara-DiC16MA liposome was found to have good transfection efficacy in HEK293, PC-3 and Mat cells compared with other three kinds of liposomes, and also maintain low cytotoxicity and better uptake capability in vitro. Furthermore, the gene silencing assay showed that Ara-DiC14MA and Ara-DiC16MA liposomes have demonstrated effective delivery and higher gene knockdown activity (>80%) in the above mentioned cells than Lipofectamine 2000. These results indicated Ara-DiC16MA can be developed for efficient and low toxic gene delivery.

Current state and challenges in developing oral vaccines

While vaccination remains the most cost effective strategy for disease prevention, communicable diseases persist as the second leading cause of death worldwide. There is a need to design safe, novel vaccine delivery methods to protect against unaddressed and emerging diseases. Development of vaccines administered orally is preferable to traditional injection-based formulations for numerous reasons including improved safety and compliance, and easier manufacturing and administration. Additionally, the oral route enables stimulation of humoral and cellular immune responses at both systemic and mucosal sites to establish broader and long-lasting protection. However, oral delivery is challenging, requiring formulations to overcome the harsh gastrointestinal (GI) environment and avoid tolerance induction to achieve effective protection. Here we address the rationale for oral vaccines, including key biological and physicochemical considerations for next-generation oral vaccine design.

Nanotechnology in Glycomics: Applications in Diagnostics, Therapy, Imaging, and Separation Processes

This review comprehensively covers the most recent achievements (from 2013) in the successful integration of nanomaterials in the field of glycomics. The first part of the paper addresses the beneficial properties of nanomaterials for the construction of biosensors, bioanalytical devices, and protocols for the detection of various analytes, including viruses and whole cells, together with their key characteristics. The second part of the review focuses on the application of nanomaterials integrated with glycans for various biomedical applications, that is, vaccines against viral and bacterial infections and cancer cells, as therapeutic agents, for in vivo imaging and nuclear magnetic resonance imaging, and for selective drug delivery. The final part of the review describes various ways in which glycan enrichment can be effectively done using nanomaterials, molecularly imprinted polymers with polymer thickness controlled at the nanoscale, with a subsequent analysis of glycans by mass spectrometry. A short section describing an active glycoprofiling by microengines (microrockets) is covered as well.

Natural Vaccine Adjuvants and Immunopotentiators Derived From Plants, Fungi, Marine Organisms, and Insects

Immunopotentiators derived from different natural sources are under investigation with varying success. This chapter gives an overview of developments from plants, fungi, marine organisms, and insects. Plant-derived immune stimulators consist of a diverse range of small molecules or large polysaccharides. Notable examples that have been assessed in both preclinical and clinical trials include saponins, tomatine, and inulin. Similarly, fungi produce a range of potential candidate molecules, with β-glucans showing the most promise. Other complex molecules that have established adjuvant activity include α-galactosylceramide (originally obtained from a marine sponge), chitosan (commonly produced from chitin from shrimps), and peptides (found in bee venom). Some organisms, for example, endophytic fungi and bees, produce immunostimulants using compounds obtained from plants. The main challenges facing this type of research and tools being developed to overcome them are examined.

Preparation of Multifunctional Liposomes as a Stable Vaccine Delivery-Adjuvant System by Procedure of Emulsification-Lyophilization

Liposomes have been proven to be useful carriers for vaccine antigens and can be modified as a versatile vaccine adjuvant-delivery system (VADS). To fulfill efficiently both functions of adjuvant and delivery, the liposomes are often modified with different functional molecules, such as lipoidal immunopotentiators, APC (antigen-presenting cell) targeting ligands, steric stabilization polymers, and charged lipids. Also, to overcome the weakness of instability, vaccines are often lyophilized as a dry product. In this chapter the procedure of emulsification-lyophilization (PEL) is introduced as an efficient method for preparing a stable anhydrous precursor to the multifunctional liposomes which bear dual modifications with APC targeting molecule of the mannosylated cholesterol and the adjuvant material of monophosphoryl lipid A. The techniques and procedures for synthesis of APC targeting molecule, i.e., the mannosylated cholesterol, and for characterization of the multifunctional liposomes are also described.

Combining different types of multifunctional liposomes loaded with ammonium bicarbonate to fabricate microneedle arrays as a vaginal mucosal vaccine adjuvant-dual delivery system (VADDS)

To develop effective mucosal vaccines, two types of multifunctional liposomes, the mannosylated lipid A-liposomes (MLLs) with a size of 200nm and the stealth lipid A-liposomes (SLLs) of 50nm, both loaded with a model antigen and NH₄HCO₃, were fabricated together into microneedles, forming the proSLL/MLL-constituted microneedle array (proSMMA), which upon rehydration dissolved rapidly recovering the initial MLLs and SLLs. Mice vaccinated with proSMMAs by vaginal mucosa patching other than conventional intradermal administration established robust antigen-specific humoral and cellular immunity at both systemic and mucosal levels, especially, in the reproductive and intestinal ducts. Further exploration demonstrated that the MLLs reconstituted from the administered proSMMAs were mostly taken up by vaginal mucosal dendritic cells, whereas the recovered SLLs trafficked directly to draining lymph nodes wherein to be picked up by macrophages. Moreover, the antigens delivered by either liposomes were also cross-presented for MHC-I displaying by APCs thanks to lysosome escape and ROS (reactive oxygen species) stimulation, both of which occurred when lysosomal acidifying the liposome-released NH₄HCO₃ into CO₂ and NH₄⁺/NH₃ to rupture lysosomes by gas expansion and to cause ROS production by excessive ammonia induction, resulting in a mixed Th1/Th2 type response which was also promoted by liposomal lipid A via activation of TLR4. In addition, vaginal vaccination of the engineered HSV2 antigen gD-loaded proSMMAs successfully protected mice from the virus challenge. Thus, the proSMMAs are in fact a vaccine adjuvant-dual delivery system capable of eliciting robust humoral and cellular immunity against the invading pathogens, especially, the sexually transmitted ones.

Oral absorption of peptides and nanoparticles across the human intestine: Opportunities, limitations and studies in human tissues

In this contribution, we review the molecular and physiological barriers to oral delivery of peptides and nanoparticles. We discuss the opportunities and predictivity of various in vitro systems with special emphasis on human intestine in Ussing chambers. First, the molecular constraints to peptide absorption are discussed. Then the physiological barriers to peptide delivery are examined. These include the gastric and intestinal environment, the mucus barrier, tight junctions between epithelial cells, the enterocytes of the intestinal epithelium, and the subepithelial tissue. Recent data from human proteome studies are used to provide information about the protein expression profiles of the different physiological barriers to peptide and nanoparticle absorption. Strategies that have been employed to increase peptide absorption across each of the barriers are discussed. Special consideration is given to attempts at utilizing endogenous transcytotic pathways. To reliably translate in vitro data on peptide or nanoparticle permeability to the in vivo situation in a human subject, the in vitro experimental system needs to realistically capture the central aspects of the mentioned barriers. Therefore, characteristics of common in vitro cell culture systems are discussed and compared to those of human intestinal tissues. Attempts to use the cell and tissue models for in vitro-in vivo extrapolation are reviewed.