Enhanced mucosal and systemic immune response with intranasal immunization of mice with HIV peptides entrapped in PLG microparticles in combination with Ulex Europaeus-I lectin as M cell target

Nanocarriers transport across the gastrointestinal barriers: The contribution to oral bioavailability via blood circulation and lymphatic pathway

Oral administration is the preferred route of drug delivery in clinical practice due to its noninvasiveness, safety, convenience, and high patient compliance. The gastrointestinal tract (GIT) plays a crucial role in facilitating the targeted delivery of oral drugs. However, the GIT presents multiple barriers that impede drug absorption, including the gastric barrier in the stomach and the mucus and epithelial barriers in the intestine. In recent decades, nanotechnology has emerged as a promising approach for overcoming these challenges by utilizing nanocarrier-based drug delivery systems such as liposomes, micelles, polymeric nanoparticles, solid lipid nanoparticles, and inorganic nanoparticles. Encapsulating drugs within nanocarriers not only protects them from degradation but also enhances their transport and absorption across the GIT, ultimately improving oral bioavailability. The aim of this review is to elucidate the mechanisms underlying nanocarrier-mediated transportation across the GIT into systemic circulation via both the blood circulation and lymphatic pathway.

Enhanced mucosal immune responses and reduced viral load in the respiratory tract of ferrets to intranasal lipid nanoparticle-based SARS-CoV-2 proteins and mRNA vaccines

BACKGROUND

Unlike the injectable vaccines, intranasal lipid nanoparticle (NP)-based adjuvanted vaccine is promising to protect against local infection and viral transmission. Infection of ferrets with SARS-CoV-2 results in typical respiratory disease and pathology akin to in humans, suggesting that the ferret model may be ideal for intranasal vaccine studies.

RESULTS

We developed SARS-CoV-2 subunit vaccine containing both Spike receptor binding domain (S-RBD) and Nucleocapsid (N) proteins (NP-COVID-Proteins) or their mRNA (NP-COVID-mRNA) and NP-monosodium urate adjuvant. Both the candidate vaccines in intranasal vaccinated aged ferrets substantially reduced the replicating virus in the entire respiratory tract. Specifically, the NP-COVID-Proteins vaccine did relatively better in clearing the virus from the nasal passage early post challenge infection. The immune gene expression in NP-COVID-Proteins vaccinates indicated increased levels of mRNA of IFNα, MCP1 and IL-4 in lungs and nasal turbinates, and IFNγ and IL-2 in lungs; while proinflammatory mediators IL-1β and IL-8 mRNA levels in lungs were downregulated. In NP-COVID-Proteins vaccinated ferrets S-RBD and N protein specific IgG antibodies in the serum were substantially increased at both day post challenge (DPC) 7 and DPC 14, while the virus neutralizing antibody titers were relatively better induced by mRNA versus the proteins-based vaccine. In conclusion, intranasal NP-COVID-Proteins vaccine induced balanced Th1 and Th2 immune responses in the respiratory tract, while NP-COVID-mRNA vaccine primarily elicited antibody responses.

CONCLUSIONS

Intranasal NP-COVID-Proteins vaccine may be an ideal candidate to elicit increased breadth of immunity against SARS-CoV-2 variants.

Nanomedicine: New Frontiers in Fighting Microbial Infections

Microbes have dominated life on Earth for the past two billion years, despite facing a variety of obstacles. In the 20th century, antibiotics and immunizations brought about these changes. Since then, microorganisms have acquired resistance, and various infectious diseases have been able to avoid being treated with traditionally developed vaccines. Antibiotic resistance and pathogenicity have surpassed antibiotic discovery in terms of importance over the course of the past few decades. These shifts have resulted in tremendous economic and health repercussions across the board for all socioeconomic levels; thus, we require ground-breaking innovations to effectively manage microbial infections and to provide long-term solutions. The pharmaceutical and biotechnology sectors have been radically altered as a result of nanomedicine, and this trend is now spreading to the antibacterial research community. Here, we examine the role that nanomedicine plays in the prevention of microbial infections, including topics such as diagnosis, antimicrobial therapy, pharmaceutical administration, and immunizations, as well as the opportunities and challenges that lie ahead.

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.

Oral and intranasal vaccines against SARS-CoV-2: Current progress, prospects, advantages, and challenges

Background

The severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has caused a deadly pandemic in the 21st century, resulting in many deaths, economic loss, and international immobility. Vaccination represents the only mechanism to defeat this virus. Several intramuscular vaccines have been approved and are currently used worldwide.

Main body

However, global mass vaccination has not been achieved owing to several limitations, including the need for expertise to administer the injection‐based vaccine, improper distribution of the vaccine, and lack of cold chain facilities, particularly in resource‐poor, low‐income countries. Mucosal vaccines are typically administered either orally or nasally, and several studies have shown promising results for developing these vaccines against SARS‐CoV‐2 that might serve as viable alternatives to current vaccines. SARS‐CoV‐2 invades the human body via oral and nasal mucosal surfaces; thus, an oral or nasal vaccine can trigger the immune system to inhibit the virus at the mucosal level, preventing further transmission via a strong mucosal and systematic immune response. Although several approaches toward developing a mucosal vaccine are currently being tested, additional attention is required.

Conclusion

In this article, the current approaches used to develop effective oral and nasal mucosal vaccines against SARS‐CoV‐2 and their benefits, prospects, and challenges have been summarized.

Advancedoral vaccine delivery strategies for improving the immunity

Infectious diseases continue to inflict a high global disease burden. The consensus is that vaccination is the most effective option against infectious diseases. Oral vaccines have unique advantages in the prevention of global pandemics due to their ease of use, high compliance, low cost, and the ability to induce both systemic and mucosal immune responses. However, challenges of adapting vaccines for oral administration remain significant. Foremost among these are enzymatic and pH-dependent degradation of antigens in the stomach and intestines, the low permeability of mucus barrier, the nonspecific uptake of antigens at the intestinal mucosal site, and the immune suppression result from the elusive immune tolerance mechanisms. Innovative delivery techniques promise great potential for improving the flexibility and efficiency of oral vaccines. A better understanding of the delivery approaches and the immunological mechanisms of oral vaccine delivery systems may provide new scientific insight and tools for developing the next-generation oral vaccine. Here, an overview of the advanced technologies in the field of oral vaccination is proposed, including mucus-penetrating nanoparticle (NP), mucoadhesive delivery vehicles, targeting antigen-presenting cell (APC) nanocarriers and enhanced paracellular delivery strategies and so on. Meanwhile, the mechanisms of delivery vectors interact with mucosal barriers are discussed.

Preliminary study on serum immunoglobulin G responses following intramuscular inoculation of adjuvanted polyhydroxyalkanoate microparticles with Pasteurella multocida vaccine in white rats

A natural biodegradable polymer, polyhydroxyalkanoate (PHA), was adjuvanted with a vaccine seed to observe the biomaterial's ability in enhancing an immune response in rats. The adjuvant potential of PHA was tested using the whole-killed Pasteurella multocida B:2 (PMB2) vaccine in Sprague Dawley (SD) rats to detect changes in serum immunoglobulin G (IgG) and immunoglobulin M (IgM) responses. A common PHA, poly(3-hydroxybutyrate) [P(3HB)], from Bacillus megaterium UMTKB-1 was constructed into microparticles using the solvent evaporation method. Twelve SD rats were divided into four treatment groups: 1) non-treatment as negative control, 2) P(3HB) adjuvant, 3) PMB2 vaccine, and 4) adjuvanted-P(3HB)/PMB2 vaccine groups, which were intramuscularly vaccinated twice. Immunoglobulins IgG and IgM levels were used as markers of the immune response induced by the adjuvanted-P(3HB)/PMB2 vaccine and analysed over an eight-week study period. The group vaccinated specifically with adjuvanted-P(3HB)/PMB2 vaccine had higher concentrations of immunoglobulins compared to other treatment groups, hence demonstrating the potential of the adjuvant to enhance immune response. Findings showed a need to delay the delivery of the second booster dose to determine the appropriate regime for the adjuvanted-P(3HB)/PMB2 vaccine.

Prospects for mucosal vaccine: shutting the door on SARS-CoV-2

The sudden emergence of a highly transmissible and pathogenic coronavirus SARS-CoV-2 in December 2019 from China and its rapid global spread has posed an international health emergency. The rapid development of an effective vaccine is imperative to control the spread of SARS-CoV-2. A number of concurrent efforts to find an effective therapeutic agent or vaccine for COVID-19 (coronavirus disease 2019) are being undertaken globally. Oral and nasal mucosal surfaces serve as the primary portal of entry for pathogens like coronaviruses in the human body. As evidenced by studies on similar coronaviruses (SARS-CoV and MERS-CoV), mucosal vaccination can provide a safe and effective means for the induction of long-lasting systemic and mucosal immunity to confer protection against SARS-CoV-2. This article summarizes the approaches to an effective mucosal vaccine formulation which can be a rewarding approach to combat the unprecedented threat posed by this emerging global pandemic.

Advances in Oral Drug Delivery for Regional Targeting in the Gastrointestinal Tract - Influence of Physiological, Pathophysiological and Pharmaceutical Factors

The oral route is by far the most common route of drug administration in the gastrointestinal tract and can be used for both systemic drug delivery and for treating local gastrointestinal diseases. It is the most preferred route by patients, due to its advantages, such as ease of use, non-invasiveness, and convenience for self-administration. Formulations can also be designed to enhance drug delivery to specific regions in the upper or lower gastrointestinal tract. Despite the clear advantages offered by the oral route, drug delivery can be challenging as the human gastrointestinal tract is complex and displays a number of physiological barriers that affect drug delivery. Among these challenges are poor drug stability, poor drug solubility, and low drug permeability across the mucosal barriers. Attempts to overcome these issues have focused on improved understanding of the physiology of the gastrointestinal tract in both healthy and diseased states. Innovative pharmaceutical approaches have also been explored to improve regional drug targeting in the gastrointestinal tract, including nanoparticulate formulations. This review will discuss the physiological, pathophysiological, and pharmaceutical considerations influencing drug delivery for the oral route of administration, as well as the conventional and novel drug delivery approaches. The translational challenges and development aspects of novel formulations will also be addressed.

Immunology-Guided Biomaterial Design for Mucosal Cancer Vaccines

Cancer of mucosal tissues is a major cause of worldwide mortality for which only palliative treatments are available for patients with late-stage disease. Engineered cancer vaccines offer a promising approach for inducing antitumor immunity. The route of vaccination plays a major role in dictating the migratory pattern of lymphocytes, and thus vaccine efficacy in mucosal tissues. Parenteral immunization, specifically subcutaneous and intramuscular, is the most common vaccination route. However, this induces marginal mucosal protection in the absence of tissue-specific imprinting signals. To circumvent this, the mucosal route can be utilized, however degradative mucosal barriers must be overcome. Hence, vaccine administration route and selection of materials able to surmount transport barriers are important considerations in mucosal cancer vaccine design. Here, an overview of mucosal immunity in the context of cancer and mucosal cancer clinical trials is provided. Key considerations are described regarding the design of biomaterial-based vaccines that will afford antitumor immune protection at mucosal surfaces, despite limited knowledge surrounding mucosal vaccination, particularly aided by biomaterials and mechanistic immune-material interactions. Finally, an outlook is given of how future biomaterial-based mucosal cancer vaccines will be shaped by new discoveries in mucosal vaccinology, tumor immunology, immuno-therapeutic screens, and material-immune system interplay.

Identifying human and murine M cells in vitro

IMPACT STATEMENT

The study of M cells, a specialized epithelial cell type found in the follicle-associated epithelium, is hampered by the lack of a universal M cell marker. As such, many studies lack reliable and universally recognized methods to identify M cells in their proposed models. As a result of this it is difficult to ascertain whether the effects observed are due to the presence of M cells or an unaccounted variable. The outcome of this review is the thorough evaluation of the many M cell markers that have been used in the literature thus far and a proposed criterion for the identification of M cells for future publications. This will hopefully lead to an improvement in the quality of future publications in this field.

Promising Plant-Derived Adjuvants in the Development of Coccidial Vaccines

Coccidial parasites cause medical and veterinary diseases worldwide, frequently leading to severe illness and important economic losses. At present, drugs, chemotherapeutics and prophylactic vaccines are still missing for most of the coccidial infections. Moreover, the development and administration of drugs and chemotherapeutics against these diseases would not be adequate in livestock, since they may generate unacceptable residues in milk and meat that would avoid their commercialization. In this scenario, prophylactic vaccines emerge as the most suitable approach. Subunit vaccines have proven to be biologically safe and economically viable, allowing researchers to choose among the best antigens against each pathogen. However, they are generally poorly immunogenic and require the addition of adjuvant compounds to the vaccine formulation. During the last decades, research involving plant immunomodulatory compounds has become an important field of study based on their potential pharmaceutical applications. Some plant molecules such as saponins, polysaccharides, lectins and heat shock proteins are being explored as candidates for adjuvant/carriers formulations. Moreover, plant-derived immune stimulatory compounds open the possibility to attain the main goal in adjuvant research: a safe and non-toxic adjuvant capable of strongly boosting and directing immune responses that could be incorporated into different vaccine formulations, including mucosal vaccines. Here, we review the immunomodulatory properties of several plant molecules and discuss their application and future perspective as adjuvants in the development of vaccines against coccidial infections.

M cell targeting engineered biomaterials for effective vaccination

Vaccines are one of the greatest medical interventions of all time and have been successful in controlling and eliminating a myriad of diseases over the past two centuries. Among several vaccination strategies, mucosal vaccines have wide clinical applications and attract considerable interest in research, showing potential as innovative and novel therapeutics. In mucosal vaccination, targeting (microfold) M cells is a frontline prerequisite for inducing effective antigen-specific immunostimulatory effects. In this review, we primarily focus on materials engineered for use as vaccine delivery platforms to target M cells. We also describe potential M cell targeting areas, methods to overcome current challenges and limitations of the field. Furthermore, we present the potential of biomaterials engineering as well as various natural and synthetic delivery technologies to overcome the challenges of M cell targeting, all of which are absent in current literature. Finally, we briefly discuss manufacturing and regulatory processes to bring a robust perspective on the feasibility and potential of this next-generation vaccine technology.

Targeting the intestinal lymphatic system: a versatile path for enhanced oral bioavailability of drugs

INTRODUCTION

The major challenge of first pass metabolism in oral drug delivery can be surmounted by directing delivery toward intestinal lymphatic system (ILS). ILS circumvents the liver and transports drug directly into systemic circulation via thoracic duct. Lipid and polymeric nanoparticles are transported into ILS through lacteal and Peyer's patches. Moreover, surface modification of nanoparticles with ligand which is specific for Peyer's patches enhances the uptake of drugs into ILS. Bioavailability enhancement by lymphatic uptake is an advantageous approach adopted by scientists today. Therefore, it is important to understand clear insight of ILS in targeted drug delivery and challenges involved in it.

AREAS COVERED

Current review includes an overview of ILS, factors governing lymphatic transport of nanoparticles and absorption mechanism of lipid and polymeric nanoparticles into ILS. Various ligands used to target Peyer's patch and their conjugation strategies to nanoparticles are explained in detail. In vitro and in vivo models used to assess intestinal lymphatic transport of molecules are discussed further.

EXPERT OPINION

Although ILS offers a versatile pathway for nanotechnology based targeted drug delivery, extensive investigations on validation of the lymphatic transport models and on the strategies for gastric protection of targeted nanocarriers have to be perceived in for excellent performance of ILS in oral drug delivery.

Outer Membrane Vesicles: Current Status and Future Direction of These Novel Vaccine Adjuvants

Adjuvants have been of great interest to vaccine formulation as immune-stimulators. Prior to the recent research in the field of immune stimulation, conventional adjuvants utilized for aluminum-based vaccinations dominated the adjuvant market. However, these conventional adjuvants have demonstrated obvious defects, including poor protective efficiency and potential side effects, which hindered their widespread circulation. Outer membrane vesicles (OMVs) naturally exist in gram-negative bacteria and are capable of engaging innate and adaptive immunity and possess intrinsic adjuvant capacity. They have shown tremendous potential for adjuvant application and have recently been successfully applied in various vaccine platforms. Adjuvants could be highly effective with the introduction of OMVs, providing complete immunity and with the benefits of low toxicity; further, OMVs might also be designed as an advanced mucosal delivery vehicle for use as a vaccine carrier. In this review, we discuss adjuvant development, and provide an overview of novel OMV adjuvants and delivery vehicles. We also suggest future directions for adjuvant research. Overall, we believe that OMV adjuvants would find high value in vaccine formulation in the future.

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.

Virus-Like Particle, Liposome, and Polymeric Particle-Based Vaccines against HIV-1

It is acknowledged that vaccines remain the best hope for eliminating the HIV-1 epidemic. However, the failure to produce effective vaccine immunogens and the inability of conventional delivery strategies to elicit the desired immune responses remains a central theme and has ultimately led to a significant roadblock in HIV vaccine development. Consequently, significant efforts have been applied to generate novel vaccine antigens and delivery agents, which mimic viral structures for optimal immune induction. Here, we review the latest developments that have occurred in the nanoparticle vaccine field, with special emphasis on strategies that are being utilized to attain highly immunogenic, systemic, and mucosal anti-HIV humoral and cellular immune responses. This includes the design of novel immunogens, the central role of antigen-presenting cells, delivery routes, and biodistribution of nanoparticles to lymph nodes. In particular, we will focus on virus-like-particle formulations and their preclinical uses within the HIV prophylactic vaccine setting.

Respiratory nanoparticle-based vaccines and challenges associated with animal models and translation

Vaccine development has had a huge impact on human health. However, there is a significant need to develop efficacious vaccines for several existing as well as emerging respiratory infectious diseases. Several challenges need to be overcome to develop efficacious vaccines with translational potential. This review focuses on two aspects to overcome some barriers — 1) the development of nanoparticle-based vaccines, and 2) the choice of suitable animal models for respiratory infectious diseases that will allow for translation. Nanoparticle-based vaccines, including subunit vaccines involving synthetic and/or natural polymeric adjuvants and carriers, as well as those based on virus-like particles offer several key advantages to help overcome the barriers to effective vaccine development. These include the ability to deliver combinations of antigens, target the vaccine formulation to specific immune cells, enable cross-protection against divergent strains, act as adjuvants or immunomodulators, allow for sustained release of antigen, enable single dose delivery, and potentially obviate the cold chain. While mouse models have provided several important insights into the mechanisms of infectious diseases, they are often a limiting step in translation of new vaccines to the clinic. An overview of different animal models involved in vaccine research for respiratory infections, with advantages and disadvantages of each model, is discussed. Taken together, advances in nanotechnology, combined with the right animal models for evaluating vaccine efficacy, has the potential to revolutionize vaccine development for respiratory infections.

Preparation and characterization of anti-HIV nanodrug targeted to microfold cell of gut-associated lymphoid tissue

The human immunodeficiency virus 1 (HIV-1) still remains one of the leading life-threatening diseases in the world. The introduction of highly active antiretroviral therapy has significantly reduced disease morbidity and mortality. However, most of the drugs have variable penetrance into viral reservoir sites, including gut-associated lymphoid tissue (GALT). Being the largest lymphoid organ, GALT plays a key role in early HIV infection and host–pathogen interaction. Many different treatment options have been proposed to eradicate the virus from GALT. However, it becomes difficult to deliver traditional drugs to the GALT because of its complex physiology. In this regard, we developed a polymer-based Pluronic nanocarrier containing anti-HIV drug called efavirenz (EFV) targeting Microfold cells (M-cells) in the GALT. M-cells are specialized epithelial cells that are predominantly present in the GALT. In this work, we have exploited this paracellular transport property of M-cells for targeted delivery of Pluronic nanocarrier tagged EFV, bioconjugated with anti-M-cell-specific antibodies to the GALT (nanodrug). Preliminary characterization showed that the nanodrug (EFV-F12-COOH) is of 140 nm size with 0.3 polydispersion index, and the zeta potential of the particles was −19.38±2.2 mV. Further, drug dissolution study has shown a significantly improved sustained release over free drugs. Binding potential of nanodrug with M-cell was also confirmed with fluorescence microscopy and in vitro uptake and release studies. The anti-HIV activity of the nanodrug was also significantly higher compared to that of free drug. This novel formulation was able to show sustained release of EFV and inhibit the HIV-1 infection in the GALT compared to the free drug. The present study has potential for our in vivo targeted nanodrug delivery system by combining traditional enteric-coated capsule technique via oral administration.

Delivery strategies to enhance oral vaccination against enteric infections

While the majority of human pathogens infect the body through mucosal sites, most licensed vaccines are injectable. In fact the only mucosal vaccine that has been widely used globally for infant and childhood vaccination programs is the oral polio vaccine (OPV) developed by Albert Sabin in the 1950s. While oral vaccines against Cholera, rotavirus and Salmonella typhi have also been licensed, the development of additional non-living oral vaccines against these and other enteric pathogens has been slow and challenging. Mucosal vaccines can elicit protective immunity at the gut mucosa, in part via antigen-specific secretory immunoglobulin A (SIgA). However, despite their advantages over the injectable route, oral vaccines face many hurdles. A key challenge lies in design of delivery strategies that can protect antigens from degradation in the stomach and intestine, incorporate appropriate immune-stimulatory adjuvants and control release at the appropriate gastrointestinal site. A number of systems including micro and nanoparticles, lipid-based strategies and enteric capsules have significant potential either alone or in advanced combined formulations to enhance intestinal immune responses. In this review we will outline the opportunities, challenges and potential delivery solutions to facilitate the development of improved oral vaccines for infectious enteric diseases.

Biocompatible anionic polymeric microspheres as priming delivery system for effetive HIV/AIDS Tat-based vaccines

Here we describe a prime-boost regimen of vaccination in Macaca fascicularis that combines priming with novel anionic microspheres designed to deliver the biologically active HIV-1 Tat protein and boosting with Tat in Alum. This regimen of immunization modulated the IgG subclass profile and elicited a balanced Th1-Th2 type of humoral and cellular responses. Remarkably, following intravenous challenge with SHIV89.6P_cy243, vaccinees significantly blunted acute viremia, as compared to control monkeys, and this control was associated with significantly lower CD4⁺ T cell depletion rate during the acute phase of infection and higher ability to resume the CD4⁺ T cell counts in the post-acute and chronic phases of infection. The long lasting control of viremia was associated with the persistence of high titers anti-Tat antibodies whose profile clearly distinguished vaccinees in controllers and viremics. Controllers, as opposed to vaccinated and viremic cynos, exhibited significantly higher pre-challenge antibody responses to peptides spanning the glutamine-rich and the RGD-integrin-binding regions of Tat. Finally, among vaccinees, titers of anti-Tat IgG1, IgG3 and IgG4 subclasses had a significant association with control of viremia in the acute and post-acute phases of infection. Altogether these findings indicate that the Tat/H1D/Alum regimen of immunization holds promise for next generation vaccines with Tat protein or other proteins for which maintenance of the native conformation and activity are critical for optimal immunogenicity. Our results also provide novel information on the role of anti-Tat responses in the prevention of HIV pathogenesis and for the design of new vaccine candidates.

Nasal delivery of PLG microparticle encapsulated defensin peptides adjuvanted gp41 antigen confers strong and long-lasting immunoprotective response against HIV-1

Defensins display immunostimulatory activities including a chemotactic effect for T lymphocytes/immature dendritic cells and secretion of pro-inflammatory cytokines suggest their role in bridging innate and adaptive immunity. We hypothesized whether defensins with separately emulsified HIV-1 immunogen would elicit peptide-specific systemic and mucosal antibody response in mice. The HIV-1 peptide alone in microsphere showed low peptide-specific antibody response in sera and different washes, while the presence of defensins markedly increased the antibody peak titre both in sera (102,400-409,600) (p < 0.05) and in washes (800-25,600) (p < 0.001). Defensins with HIV-1 peptide were showing 43.0-83.2% and 38.7-72.3% in vitro neutralization against laboratory isolates in serum and lavage samples, respectively, higher than HIV-1 peptide alone. Our findings may have implications in the development of new mucosal adjuvant for AIDS vaccination.

Nanomedicine in the Management of Microbial Infection - Overview and Perspectives

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

Intranasal DNA Vaccine for Protection against Respiratory Infectious Diseases: The Delivery Perspectives

Intranasal delivery of DNA vaccines has become a popular research area recently. It offers some distinguished advantages over parenteral and other routes of vaccine administration. Nasal mucosa as site of vaccine administration can stimulate respiratory mucosal immunity by interacting with the nasopharyngeal-associated lymphoid tissues (NALT). Different kinds of DNA vaccines are investigated to provide protection against respiratory infectious diseases including tuberculosis, coronavirus, influenza and respiratory syncytial virus (RSV) etc. DNA vaccines have several attractive development potential, such as producing cross-protection towards different virus subtypes, enabling the possibility of mass manufacture in a relatively short time and a better safety profile. The biggest obstacle to DNA vaccines is low immunogenicity. One of the approaches to enhance the efficacy of DNA vaccine is to improve DNA delivery efficiency. This review provides insight on the development of intranasal DNA vaccine for respiratory infections, with special attention paid to the strategies to improve the delivery of DNA vaccines using non-viral delivery agents.

M cell-targeting strategy facilitates mucosal immune response and enhances protection against CVB3-induced viral myocarditis elicited by chitosan-DNA vaccine

Efficient delivery of antigen to mucosal associated lymphoid tissue is a first and critical step for successful induction of mucosal immunity by vaccines. Considering its potential transcytotic capability, M cell has become a more and more attractive target for mucosal vaccines. In this research, we designed an M cell-targeting strategy by which mucosal delivery system chitosan (CS) was endowed with M cell-targeting ability via conjugating with a CPE30 peptide, C terminal 30 amino acids of clostridium perfringens enterotoxin (CPE), and then evaluated its immune-enhancing ability in the context of coxsackievirus B3 (CVB3)-specific mucosal vaccine consisting of CS and a plasmid encoding CVB3 predominant antigen VP1. It had shown that similar to CS-pVP1, M cell-targeting CPE30-CS-pVP1 vaccine appeared a uniform spherical shape with about 300 nm diameter and +22 mV zeta potential, and could efficiently protect DNA from DNase I digestion. Mice were orally immunized with 4 doses of CPE30-CS-pVP1 containing 50 μg pVP1 at 2-week intervals and challenged with CVB3 4 weeks after the last immunization. Compared with CS-pVP1 vaccine, CPE30-CS-pVP1 vaccine had no obvious impact on CVB3-specific serum IgG level and splenic T cell immune responses, but significantly increased specific fecal SIgA level and augmented mucosal T cell immune responses. Consequently, much milder myocarditis and lower viral load were witnessed in CPE30-CS-pVP1 immunized group. The enhanced immunogenicity and immunoprotection were associated with the M cell-targeting ability of CPE30-CS-pVP1 which improved its mucosal uptake and transcytosis. Our findings indicated that CPE30-CS-pVP1 may represent a novel prophylactic vaccine against CVB3-induced myocarditis, and this M cell-targeting strategy indeed could be applied as a promising and universal platform for mucosal vaccine development.

An innovative approach to induce cross-protective immunity against porcine reproductive and respiratory syndrome virus in the lungs of pigs through adjuvanted nanotechnology-based vaccination

Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating respiratory disease of pigs. The disease is caused by the PRRS virus (PRRSV), an Arterivirus which is a highly mutating RNA virus. Widely used modified live PRRSV vaccines have failed to prevent PRRS outbreaks and reinfections; moreover, safety of the live virus vaccines is questionable. Though poorly immunogenic, inactivated PRRSV vaccine is safe. The PRRSV infects primarily the lung macrophages. Therefore, we attempted to strengthen the immunogenicity of inactivated/killed PRRSV vaccine antigens (KAg), especially in the pig respiratory system, through: 1) entrapping the KAg in biodegradable poly(lactic-co-glycolic acid) nanoparticles (NP-KAg); 2) coupling the NP-KAg with a potent mucosal adjuvant, whole cell lysate of Mycobacterium tuberculosis (M. tb WCL); and 3) delivering the vaccine formulation twice intranasally to growing pigs. We have previously shown that a single dose of NP-KAg partially cleared the challenged heterologous PRRSV. Recently, we reported that NP-KAg coupled with unentrapped M. tb WCL significantly cleared the viremia of challenged heterologous PRRSV. Since PRRSV is primarily a lung disease, our goal in this study was to investigate lung viral load and various immune correlates of protection at the lung mucosal surfaces and its parenchyma in vaccinated heterologous PRRSV-challenged pigs. Our results indicated that out of five different vaccine-adjuvant formulations, the combination of NP-KAg and unentrapped M. tb WCL significantly cleared detectable replicating infective PRRSV with a tenfold reduction in viral RNA load in the lungs, associated with substantially reduced gross and microscopic lung pathology. Immunologically, strong humoral (enhanced virus neutralization titers by high avidity antibodies) and cell-mediated immune responses (augmented population of interferon-γ secreting CD4(+) and CD8(+) lymphocytes and reduced secretion of immunosuppressive cytokines) in the lungs were observed. In conclusion, combination of NP-KAg and soluble M. tb WCL elicits broadly cross-protective anti-PRRSV immunity in the pig respiratory system.

Imaging murine NALT following intranasal immunization with flagellin-modified circumsporozoite protein malaria vaccines

Intranasal (IN) immunization with a Plasmodium circumsporozoite (CS) protein conjugated to flagellin, a Toll-like receptor 5 agonist, was found to elicit antibody-mediated protective immunity in our previous murine studies. To better understand IN-elicited immune responses, we examined the nasopharynx-associated lymphoid tissue (NALT) in immunized mice and the interaction of flagellin-modified CS with murine dendritic cells (DCs) in vitro. NALT of immunized mice contained a predominance of germinal center (GC) B cells and increased numbers of CD11c+ DCs localized beneath the epithelium and within the GC T-cell area. We detected microfold cells distributed throughout the NALT epithelial cell layer and DC dendrites extending into the nasal cavity, which could potentially function in luminal CS antigen uptake. Flagellin-modified CS taken up by DCs in vitro was initially localized within intracellular vesicles followed by a cytosolic distribution. Vaccine modifications to enhance delivery to the NALT and specifically target NALT antigen-presenting cell populations will advance development of an efficacious needle-free vaccine for the 40% of the world's population at risk of malaria.

Adjuvanted poly(lactic-co-glycolic) acid nanoparticle-entrapped inactivated porcine reproductive and respiratory syndrome virus vaccine elicits cross-protective immune response in pigs

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), is an economically devastating disease, causing daily losses of approximately $3 million to the US pork industry. Current vaccines have failed to completely prevent PRRS outbreaks. Recently, we have shown that poly(lactic-co-glycolic) acid (PLGA) nanoparticle-entrapped inactivated PRRSV vaccine (NP-KAg) induces a cross-protective immune response in pigs. To further improve its cross-protective efficacy, the NP-KAg vaccine formulation was slightly modified, and pigs were coadministered the vaccine twice intranasally with a potent adjuvant: Mycobacterium tuberculosis whole-cell lysate. In vaccinated virulent heterologous PRRSV-challenged pigs, the immune correlates in the blood were as follows: 1) enhanced PRRSV-specific antibody response with enhanced avidity of both immunoglobulin (Ig)-G and IgA isotypes, associated with augmented virus-neutralizing antibody titers; 2) comparable and increased levels of virus-specific IgG₁ and IgG₂ antibody subtypes and production of high levels of both T-helper (Th)-1 and Th2 cytokines, indicative of a balanced Th1–Th2 response; 3) suppressed immunosuppressive cytokine response; 4) increased frequency of interferon-γ⁺ lymphocyte subsets and expanded population of antigen-presenting cells; and most importantly 5) complete clearance of detectable replicating challenged heterologous PRRSV and close to threefold reduction in viral ribonucleic acid load detected in the blood. In conclusion, intranasal delivery of adjuvanted NP-KAg vaccine formulation to growing pigs elicited a broadly cross-protective immune response, showing the potential of this innovative vaccination strategy to prevent PRRS outbreaks in pigs. A similar approach to control other respiratory diseases in food animals and humans appears to be feasible.

Protective humoral immunity elicited by a needle-free malaria vaccine comprised of a chimeric Plasmodium falciparum circumsporozoite protein and a Toll-like receptor 5 agonist, flagellin

Immunization with Plasmodium sporozoites can elicit high levels of sterile immunity, and neutralizing antibodies from protected hosts are known to target the repeat region of the circumsporozoite (CS) protein on the parasite surface. CS-based subunit vaccines have been hampered by suboptimal immunogenicity and the requirement for strong adjuvants to elicit effective humoral immunity. Pathogen-associated molecular patterns (PAMPs) that signal through Toll-like receptors (TLRs) can function as potent adjuvants for innate and adaptive immunity. We examined the immunogenicity of recombinant proteins containing a TLR5 agonist, flagellin, and either full-length or selected epitopes of the Plasmodium falciparum CS protein. Mice immunized with either of the flagellin-modified CS constructs, administered intranasally (i.n.) or subcutaneously (s.c.), developed similar levels of malaria-specific IgG1 antibody and interleukin-5 (IL-5)-producing T cells. Importantly, immunization via the i.n. but not the s.c. route elicited sporozoite neutralizing antibodies capable of inhibiting >90% of sporozoite invasion in vitro and in vivo, as measured using a transgenic rodent parasite expressing P. falciparum CS repeats. These findings demonstrate that functional sporozoite neutralizing antibody can be elicited by i.n. immunization with a flagellin-modified P. falciparum CS protein and raise the potential of a scalable, safe, needle-free vaccine for the 40% of the world's population at risk of malaria.

Targeted nasal vaccination provides antibody-independent protection against Staphylococcus aureus

Despite showing promise in preclinical models, anti-Staphylococcus aureus vaccines have failed in clinical trials. To date, approaches have focused on neutralizing/opsonizing antibodies; however, vaccines exclusively inducing cellular immunity have not been studied to formally test whether a cellular-only response can protect against infection. We demonstrate that nasal vaccination with targeted nanoparticles loaded with Staphylococcus aureus antigen protects against acute systemic S. aureus infection in the absence of any antigen-specific antibodies. These findings can help inform future developments in staphylococcal vaccine development and studies into the requirements for protective immunity against S. aureus.

Microfold (M) cells: important immunosurveillance posts in the intestinal epithelium

The transcytosis of antigens across the gut epithelium by microfold cells (M cells) is important for the induction of efficient immune responses to some mucosal antigens in Peyer's patches. Recently, substantial progress has been made in our understanding of the factors that influence the development and function of M cells. This review highlights these important advances, with particular emphasis on: the host genes which control the functional maturation of M cells; how this knowledge has led to the rapid advance in our understanding of M-cell biology in the steady state and during aging; molecules expressed on M cells which appear to be used as "immunosurveillance" receptors to sample pathogenic microorganisms in the gut; how certain pathogens appear to exploit M cells to infect the host; and finally how this knowledge has been used to specifically target antigens to M cells to attempt to improve the efficacy of mucosal vaccines.

Modulation of HIV peptide antigen specific cellular immune response by synthetic α- and β-defensin peptides

Defensin peptides have their direct role in host defense against microbial infection as innate molecules and also thought to contribute to adaptive immunity by recruiting naïve T-cells and immature dendritic cells at the site of infection through CCR6 receptor. The main aim of the present study is to investigate the efficacy of defensins for the induction of cell mediated immune response against the peptide antigen of HIV-1 encapsulated in PLG microparticles through intranasal (IN) route in mice model. To characterized, we have analyzed T-cell proliferation, Th1/Th2 cytokines, β-chemokines production and IFN-γ/perforin secretion from CD4(+)/CD8(+) T-cells in response to HIV immunogen alone and with defensins at different mucosal site i.e. lamina propria (LP), spleen (SP) and peyer's patches (PP). The cellular immunogenicity of HIV peptide with defensin formulations showed a significantly higher (p<0.001) proliferation response as compared to individual HIV peptide. The enhanced cytokines measurement profile showed mixed Th1 and Th2 type of peptide specific immune response by the incorporation of defensins. In the continuation, enhancement in MIP-1α and RANTES level was also observed in HIV peptide-defensin formulations. The FACS data had revealed that CD4(+)/CD8(+) T-cells showed significantly (p<0.001) higher IFN-γ and perforin secretion in HIV with defensin peptide formulations than HIV antigen alone group. Thus, the study emphasized here that defensin peptides have a potential role as mucosal adjuvant, might be responsible for the induction of cell mediated immunity when administered in mice through IN route with HIV peptide antigen.

The immunomodulatory effect of plant lectins: a review with emphasis on ArtinM properties

Advances in the glycobiology and immunology fields have provided many insights into the role of carbohydrate-protein interactions in the immune system. We aim to present a comprehensive review of the effects that some plant lectins exert as immunomodulatory agents, showing that they are able to positively modify the immune response to certain pathological conditions, such as cancer and infections. The present review comprises four main themes: (1) an overview of plant lectins that exert immunomodulatory effects and the mechanisms accounting for these activities; (2) general characteristics of the immunomodulatory lectin ArtinM from the seeds of Artocarpus heterophyllus; (3) activation of innate immunity cells by ArtinM and consequent induction of Th1 immunity; (4) resistance conferred by ArtinM administration in infections with intracellular pathogens, such as Leishmania (Leishmania) major, Leishmania (Leishmania) amazonensis, and Paracoccidioides brasiliensis. We believe that this review will be a valuable resource for more studies in this relatively neglected area of research, which has the potential to reveal carbohydrate targets for novel prophylactic and therapeutic strategies.

Intestinal receptor targeting for peptide delivery: an expert's personal perspective on reasons for failure and new opportunities

The technology has been available more than 25 years that would enable the oral delivery of vaccines, proteins and peptides, thus avoiding the need for injection. To this day, injection is still the mode of delivery, yet not the main mode of choice. This review focuses on several of the potential modes for oral delivery of peptides, proteins and vaccines. Additionally, the review will provide the reader with an insight into the problems and potential solutions for several of these modes of oral delivery of peptides and proteins.

M cell-targeted mucosal vaccine strategies

Immune responses in the aerodigestive tract are characterized by production and transport of specific IgA antibodies across the epithelium to act as a first line of defense against pathogens in the external environment. To sample antigens on mucosal surfaces in the intestine and upper respiratory tract, the immune system relies on a close collaboration between specialized antigen-sampling epithelial M cells and lymphoid cells. Depending on various factors, local antigen presentation in the mucosal tissue leads to tolerance or initiation of an active immune response. Recently, molecules that could be used to target vaccine antigens to apical M cell surfaces have been identified. Here we review the M cell-targeted vaccine strategy, an approach that could be used to enhance uptake and efficacy of vaccines delivered in the nasal cavity or intestine.

Mucosal vaccine design and delivery

Mucosal surfaces are a major portal of entry for many human pathogens that are the cause of infectious diseases worldwide. Vaccines capable of eliciting mucosal immune responses can fortify defenses at mucosal front lines and protect against infection. However, most licensed vaccines are administered parenterally and fail to elicit protective mucosal immunity. Immunization by mucosal routes may be more effective at inducing protective immunity against mucosal pathogens at their sites of entry. Recent advances in our understanding of mucosal immunity and identification of correlates of protective immunity against specific mucosal pathogens have renewed interest in the development of mucosal vaccines. Efforts have focused on efficient delivery of vaccine antigens to mucosal sites that facilitate uptake by local antigen-presenting cells to generate protective mucosal immune responses. Discovery of safe and effective mucosal adjuvants are also being sought to enhance the magnitude and quality of the protective immune response.

Chimeric flagellin expressed by Salmonella typhimurium induces an ESAT-6-specific Th1-type immune response and CTL effects following intranasal immunization

The flagellin component FliC of Salmonella typhimurium is capable of activating the innate immune system via specific interactions with TLR5 and can also act as a carrier of foreign antigen to elicit antigen-specific immune responses. Thus, we constructed an attenuated Salmonella strain SL5928(fliC/esat) expressing chimeric flagellin that contained the ESAT-6 antigen coding sequence of Mycobacterium tuberculosis inserted into the highly variable region of the Salmonella flagellin coding gene fliC(i). The chimeric flagellin functioned normally, as demonstrated using a flagella swarming assay and electron microscopy. To analyze the effects of chimeric flagellin, the cell-mediated immune response and cytotoxic T lymphocyte (CTL) effects specific for ESAT-6 antigen were tested after intranasal immunization of mice with flagellated Salmonella SL5928(fliC/esat). The results showed that SL5928(fliC/esat) intranasal immunization can strongly elicit an ESAT-6-specific T helper (Th) 1-type immune response in mucosal lymphoid tissues, such as nasopharynx-associated lymph nodes, lung and Peyer's patches, and a Th1/Th2 response was elicited in spleen and mesenteric lymph nodes. Furthermore, intranasal immunization of SL5928(fliC/esat) produced efficient CTL effects, as demonstrated using a 5- and 6-carboxyfluorescein diacetate succinimidyl ester (CFSE) assay. Thus, our study revealed that Salmonella flagellin acts as a carrier for foreign antigen and triggers strong Th1 and CTL responses during intranasal immunization. Chimeric flagellin is potentially an effective strategy for the development of novel vaccines against tuberculosis in humans and animals.

Nano-microparticles as immune adjuvants: correlating particle sizes and the resultant immune responses

The development of novel immune adjuvants is emerging as a significant area of vaccine delivery based on the continued necessity to amplify immune responses to a wide array of new antigens that are poorly immunogenic. This article specifically focuses on the application of nanoparticles and microparticles as vaccine adjuvants. Many investigators are in agreement that the size of the particles is crucial to their adjuvant activities. However, reports on correlating the size of particle-based adjuvants and the resultant immune responses have been conflicting, with investigators on both sides of the fence with impressive data in support of the effectiveness of particles with small sizes (submicron) over those with larger sizes (micron) and vice versa, while other investigators reported data that showed submicron- and micron-sized particles are effective to the same degree as immune adjuvants. We have generated a list of biological, immunological and, more importantly, vaccine formulation parameters that may have contributed to the inconsistency from different studies and made recommendations on future studies attempting to correlate the size of particulate adjuvants and the immune responses induced. The information gathered could lead to strategies to optimize the performance of nano-microparticles as immune adjuvants.