Microneedle-based intradermal delivery of the anthrax recombinant protective antigen vaccine

Diagnostic, Therapeutic, and Theranostic Multifunctional Microneedles

Microneedles (MNs) have maintained their popularity in therapeutic and diagnostic medical applications throughout the past decade. MNs are originally designed to gently puncture the stratum corneum layer of the skin and have lately evolved into intelligent devices with functions including bodily fluid extraction, biosensing, and drug administration. MNs offer limited invasiveness, ease of application, and minimal discomfort. Initially manufactured solely from metals, MNs are now available in polymer-based varieties. MNs can be used to create systems that deliver drugs and chemicals uniformly, collect bodily fluids, and are stimulus-sensitive. Although these advancements are favorable in terms of biocompatibility and production costs, they are insufficient for the therapeutic use of MNs. This is the first comprehensive review that discusses individual MN functions toward the evolution and development of smart and multifunctional MNs for a variety of novel and impactful future applications. The study examines fabrication techniques, application purposes, and experimental details of MN constructs that perform multiple functions concurrently, including sensing, drug-molecule release, sampling, and remote communication capabilities. It is highly likely that in the near future, MN-based smart devices will be a useful and important component of standard medical practice for different applications.

Protection against Severe Illness versus Immunity-Redefining Vaccine Effectiveness in the Aftermath of COVID-19

Anti-SARS-CoV-2 vaccines have played a pivotal role in reducing the risk of developing severe illness from COVID-19, thus helping end the COVID-19 global public health emergency after more than three years. Intriguingly, as SARS-CoV-2 variants emerged, individuals who were fully vaccinated did get infected in high numbers, and viral loads in vaccinated individuals were as high as those in the unvaccinated. However, even with high viral loads, vaccinated individuals were significantly less likely to develop severe illness; this begs the question as to whether the main effect of anti-SARS-CoV-2 vaccines is to confer protection against severe illness or immunity against infection. The answer to this question is consequential, not only to the understanding of how anti-SARS-CoV-2 vaccines work, but also to public health efforts against existing and novel pathogens. In this review, we argue that immune system sensitization-desensitization rather than sterilizing immunity may explain vaccine-mediated protection against severe COVID-19 illness even when the SARS-CoV-2 viral load is high. Through the lessons learned from COVID-19, we make the case that in the disease's aftermath, public health agencies must revisit healthcare policies, including redefining the term "vaccine effectiveness."

Exploring new frontiers in drug delivery with minimally invasive microneedles: fabrication techniques, biomedical applications and regulatory aspects

INTRODUCTION

Transdermal drug delivery is limited by the stratum corneum, inhibiting the therapeutic potential of the permeants. Microneedles (MN) have opened new frontiers in transdermal drug delivery systems. These micro-sized needles offer painless and accentuated delivery of drugs even with high molecular weights.

AREAS COVERED

The review embodies drug delivery strategies with microneedles with a description of MN types and fabrication techniques using various materials. The application of MN is not limited to drug delivery, but it also encompasses in vaccine delivery, diagnosis, phlebotomy and even in the cosmetic industry. The review also tabulates microneedle-based marketed formulations. In a nutshell, we aim to present a panoramic view of microneedles including the design, applications, and regulatory aspects of MN.

EXPERT OPINION

With the availability of numerous materials at the disposal of pharmaceutical scientists; the microneedle-based drug delivery technology has offered significant interventions towards the management of chronic maladies including cardiovascular disorders, diabetes, asthma, mental depression, etc. As happens with any new technology there are concerns with MN also such as biocompatibility issues with the material used for the fabrication. Nevertheless, the pharmaceutical industry must strive for preparing harmless, efficient, and cost-effective MN based delivery systems for wider acceptance and patient compliance.

Aerosolized Intratracheal Inoculation of Recombinant Protective Antigen (rPA) Vaccine Provides Protection Against Inhalational Anthrax in B10.D2-Hc0 Mice

Anthrax caused by Bacillus anthracis is a fatal zoonotic disease with a high lethality and poor prognosis. Inhalational anthrax is the most severe of the three forms of anthrax. The currently licensed commercial human anthrax vaccines require a complex immunization procedure for efficacy and have side effects that limit its use in emergent situations. Thus, development of a better anthrax vaccine is necessary. In this study, we evaluate the potency and efficacy of aerosolized intratracheal (i.t.) inoculation with recombinant protective antigen (rPA) subunit vaccines against aerosolized B. anthracis Pasteur II spores (an attenuated strain) challenge in a B10.D2-Hc⁰ mouse (deficient in complement component C5) model. Immunization of rPA in liquid, powder or powder reconstituted formulations via i.t. route conferred 100% protection against a 20× LD₅₀ aerosolized Pasteur II spore challenge in mice, compared with only 50% of subcutaneous (s.c.) injection with liquid rPA. Consistently, i.t. inoculation of rPA vaccines induced a higher lethal toxin (LeTx) neutralizing antibody titer, a stronger lung mucosal immune response and a greater cellular immune response than s.c. injection. Our results demonstrate that immunization with rPA dry powder vaccine via i.t. route may provide a stable and effective strategy to improve currently available anthrax vaccines and B10.D2-Hc⁰ mice challenged with B. anthracis attenuated strains might be an alternative model for anthrax vaccine candidate screening.

Advances and challenges in nintedanib drug delivery

INTRODUCTION

Nintedanib (N.T.B) is an orally administered tyrosine kinase inhibitor that has been approved recently by U.S.F.D.A for idiopathic pulmonary fibrosis (I.P.F) and systemic sclerosis-associated interstitial lung disease (S.Sc-I.L.D). N.T.B is also prescribed in COVID-19 patients associated with I.P.F. However, it has an extremely low bioavailability of around 4.7%, and hence, researchers are attempting to address this drawback by different approaches.

AREAS COVERED

This review article focuses on enlisting all the formulation attempts explored by researchers to increase the bioavailability of N.T.B while also providing meaningful insight into the unexplored areas in formulation development, such as targeting of the lymphatic system and transdermal delivery. All the patents on the formulation development of N.T.B have also been summarized.

EXPERT OPINION

N.T.B has the potential to act on multiple diseases that are still being discovered, but its extremely low bioavailability is a challenge that is to be dealt with for obtaining the full benefit. Few studies have been performed aiming at improving the bioavailability, but there are unexplored areas that can be used, a few of which are explained in this article. However, the ability to reproduce laboratory results when scaling up to the industry level is the only factor to be taken into consideration.

An overview of microneedle applications, materials, and fabrication methods

Microneedle-based microdevices promise to expand the scope for delivery of vaccines and therapeutic agents through the skin and withdrawing biofluids for point-of-care diagnostics - so-called theranostics. Unskilled and painless applications of microneedle patches for blood collection or drug delivery are two of the advantages of microneedle arrays over hypodermic needles. Developing the necessary microneedle fabrication processes has the potential to dramatically impact the health care delivery system by changing the landscape of fluid sampling and subcutaneous drug delivery. Microneedle designs which range from sub-micron to millimetre feature sizes are fabricated using the tools of the microelectronics industry from metals, silicon, and polymers. Various types of subtractive and additive manufacturing processes have been used to manufacture microneedles, but the development of microneedle-based systems using conventional subtractive methods has been constrained by the limitations and high cost of microfabrication technology. Additive manufacturing processes such as 3D printing and two-photon polymerization fabrication are promising transformative technologies developed in recent years. The present article provides an overview of microneedle systems applications, designs, material selection, and manufacturing methods.

Recent Advances in Microneedle-Based Sensors for Sampling, Diagnosis and Monitoring of Chronic Diseases

Chronic diseases (CDs) are noncommunicable illnesses with long-term symptoms accounting for ~70% of all deaths worldwide. For the diagnosis and prognosis of CDs, accurate biomarker detection is essential. Currently, the detection of CD-associated biomarkers is employed through complex platforms with certain limitations in their applicability and performance. There is hence unmet need to present innovative strategies that are applicable to the point-of-care (PoC) settings, and also, provide the precise detection of biomarkers. On the other hand, especially at PoC settings, microneedle (MN) technology, which comprises micron-size needles arranged on a miniature patch, has risen as a revolutionary approach in biosensing strategies, opening novel horizons to improve the existing PoC devices. Various MN-based platforms have been manufactured for distinctive purposes employing several techniques and materials. The development of MN-based biosensors for real-time monitoring of CD-associated biomarkers has garnered huge attention in recent years. Herein, we summarize basic concepts of MNs, including microfabrication techniques, design parameters, and their mechanism of action as a biosensing platform for CD diagnosis. Moreover, recent advances in the use of MNs for CD diagnosis are introduced and finally relevant clinical trials carried out using MNs as biosensing devices are highlighted. This review aims to address the potential use of MNs in CD diagnosis.

A Comprehensive Review of Microneedles: Types, Materials, Processes, Characterizations and Applications

Drug delivery through the skin offers many advantages such as avoidance of hepatic first-pass metabolism, maintenance of steady plasma concentration, safety, and compliance over oral or parenteral pathways. However, the biggest challenge for transdermal delivery is that only a limited number of potent drugs with ideal physicochemical properties can passively diffuse and intercellularly permeate through skin barriers and achieve therapeutic concentration by this route. Significant efforts have been made toward the development of approaches to enhance transdermal permeation of the drugs. Among them, microneedles represent one of the microscale physical enhancement methods that greatly expand the spectrum of drugs for transdermal and intradermal delivery. Microneedles typically measure 0.1-1 mm in length. In this review, microneedle materials, fabrication routes, characterization techniques, and applications for transdermal delivery are discussed. A variety of materials such as silicon, stainless steel, and polymers have been used to fabricate solid, coated, hollow, or dissolvable microneedles. Their implications for transdermal drug delivery have been discussed extensively. However, there remain challenges with sustained delivery, efficacy, cost-effective fabrication, and large-scale manufacturing. This review discusses different modes of characterization and the gaps in manufacturing technologies associated with microneedles. This review also discusses their potential impact on drug delivery, vaccine delivery, disease diagnostic, and cosmetics applications.

Translation of Polymeric Microneedles for Treatment of Human Diseases: Recent Trends, Progress, and Challenges

The ongoing search for biodegradable and biocompatible microneedles (MNs) that are strong enough to penetrate skin barriers, easy to prepare, and can be translated for clinical use continues. As such, this review paper is focused upon discussing the key points (e.g., choice polymeric MNs) for the translation of MNs from laboratory to clinical practice. The review reveals that polymers are most appropriately used for dissolvable and swellable MNs due to their wide range of tunable properties and that natural polymers are an ideal material choice as they structurally mimic native cellular environments. It has also been concluded that natural and synthetic polymer combinations are useful as polymers usually lack mechanical strength, stability, or other desired properties for the fabrication and insertion of MNs. This review evaluates fabrication methods and materials choice, disease and health conditions, clinical challenges, and the future of MNs in public healthcare services, focusing on literature from the last decade.

Microneedles in Smart Drug Delivery

Significance: In biomedical setup, at large, and drug delivery, in particular, transdermal patches, hypodermal needles, and/or dermatological creams with the topical appliance are among the most widely practiced routes for transdermal drug delivery. Owing to the stratum corneum layer of the skin, traditional drug delivery methods are inefficient, and the effect of the administered therapeutic cues is limited. Recent Advances: The current advancement at the microlevel and nanolevel has revolutionized the drug delivery sector. Particularly, various types of microneedles (MNs) are becoming popular for drug delivery applications because of safety, patient compliance, and smart action. Critical Issues: Herein, we reviewed state-of-the-art MNs as a smart and sophisticated drug delivery approach. Following a brief introduction, the drug delivery mechanism of MNs is discussed. Different types of MNs, that is, solid, hollow, coated, dissolving, and hydrogel forming, are discussed with suitable examples. The latter half of the work is focused on the applied perspective and clinical translation of MNs. Furthermore, a detailed overview of clinical applications and future perspectives is also included in this review. Future Directions: Regardless of ongoing technological and clinical advancement, the focus should be diverted to enhance the efficacy and strength of MNs. Besides, the possible immune response or interference should also be avoided for successful clinical translation of MNs as an efficient drug delivery system.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Microneedle Systems for Vaccine Delivery: the story so far

INTRODUCTION

Vaccine delivery via a microneedle (MN) system has been identified as a potential alternative to conventional vaccine delivery. MN can be self-administered, is pain-free and is capable of producing superior immunogenicity. Over the last few decades, significant research has been carried out in this area, and this review aims to provide a comprehensive picture on the progress of this delivery platform.

AREAS COVERED

This review highlights the potential role of skin as a vaccine delivery route using a microneedle system, examines recent advancements in microneedle fabrication techniques, and provides an update on potential preclinical and clinical studies on vaccine delivery through microneedle systems against various infectious diseases. Articles for the review study were searched electronically in PubMed, Google, Google Scholar, and Science Direct using specific keywords to cover the scope of the article. The advanced search strategy was employed to identify the most relevant articles.

EXPERT OPINION

A significant number of MN mediated vaccine candidates have shown promising results in preclinical and clinical trials. The recent emergence of cleanroom free, 3D or additive manufacturing of MN systems and stability, together with the dose-sparing capacity of the Nanopatch® system, have made this platform, commercially, highly lucrative.

Needleless or Noninvasive Delivery Technology

Injections of drugs or vaccines have become an indispensable part of living systems. Introduction to injections begins from the vaccination regimen at the neonatal stage and continues throughout the life span of an individual. Conventionally, injections are administered using hypodermic needles and syringes. These usually inject the liquid in the muscle, thus making intramuscular injections the most common form of administration. Although hypodermic syringes have been a clinician's tool in global vaccination efforts, they also have a set of undesirable characteristics. Pathogen transmission in case of HIV and HBV is one of the deadliest disadvantages of the needle-based injection system. Generation of plastic wastes in clinics, needlestick injury, and most importantly, pain associated with needle-based injections are a few more reasons of concern. In light of these issues, developing needle-free injection systems has excited researchers across the globe since the 1950s. Significant advancement has been reported in this field and various needle-free injection systems have been developed and are in clinical practice. This article briefly describes the history of needle-free injection systems and provides a detailed account of a few well-known methods of needle-less injections available.

Progress in microneedle array patch (MAP) for vaccine delivery

A microneedle array patch (MAP) has been developed as a new delivery system for vaccines. Preclinical and clinical trials with a vaccine MAP showed improved stability, safety, and immunological efficacy compared to conventional vaccine administration. Various vaccines can be delivered with a MAP. Currently, microneedle manufacturers can mass-produce pharmaceutical MAP and cosmetic MAP and this mass-production system can be adapted to produce a vaccine MAP. Clinical trials with a vaccine MAP have shown comparable efficacy with conventional administration, and discussions about regulations for a vaccine MAP are underway. However, there are concerns of reasonable cost, mass production, efficacy, and safety standards that meet FDA approval, as well as the need for feedback regarding the best method of administration. Currently, microneedles have been studied for the delivery of many kinds of vaccines, and preclinical and clinical studies of vaccine microneedles are in progress. For the foreseeable future, some vaccines will continue to be administered with syringes and needles while the use of a vaccine MAP continues to be improved because of the advantages of less pain, self-administration, improved stability, convenience, and safety.

Intradermal and transdermal drug delivery using microneedles - Fabrication, performance evaluation and application to lymphatic delivery

The progress in microneedle research is evidenced by the transition from simple 'poke and patch' solid microneedles fabricated from silicon and stainless steel to the development of bioresponsive systems such as hydrogel-forming and dissolving microneedles. In this review, we provide an outline on various microneedle fabrication techniques which are currently employed. As a range of factors, including materials, geometry and design of the microneedles, affect the performance, it is important to understand the relationships between them and the resulting delivery of therapeutics. Accordingly, there is a need for appropriate methodologies and techniques for characterization and evaluation of microneedle performance, which will also be discussed. As the research expands, it has been observed that therapeutics delivered via microneedles has gained expedited access to the lymphatics, which makes them a favorable delivery method for targeting the lymphatic system. Such opportunity is valuable in the area of vaccination and treatment of lymphatic disorders, which is the final focus of the review.

Understanding the basis of transcutaneous vaccine delivery

Under many circumstances, prophylactic immunizations are considered as the only possible strategy to control infectious diseases. Considerable efforts are typically invested in immunogen selection but, erroneously, the route of administration is not usually a major concern despite the fact that it can strongly influence efficacy. The skin is now considered a key component of the lymphatic system with tremendous potential as a target for vaccination. The purpose of this review is to present the immunological basis of the skin-associated lymphoid tissue, so as to provide understanding of the skin vaccination strategies. Several strategies are currently being developed for the transcutaneous delivery of antigens. The classical, mechanical or chemical disruptions versus the newest approaches based on microneedles for antigen delivery through the skin are discussed herein.

Vaccines against anthrax based on recombinant protective antigen: problems and solutions

Introduction: Anthrax is a dangerous bio-terror agent because Bacillus anthracis spores are highly resilient and can be easily aerosolized and disseminated. There is a threat of deliberate use of anthrax spores aerosol that could lead to serious fatal diseases outbreaks. Existing control measures against inhalation form of the disease are limited. All of this has provided an impetus to the development of new generation vaccines. Areas сovered: This review is devoted to challenges and achievements in the design of vaccines based on the anthrax recombinant protective antigen (rPA). Scientific databases have been searched, focusing on causes of PA instability and solutions to this problem, including new approaches of rPA expression, novel rPA-based vaccines formulations as well as the simultaneous usage of PA with other anthrax antigens. Expert opinion: PA is a central anthrax toxin component, playing a key role in the defense against encapsulated and unencapsulated strains. Subunit rPA-based vaccines have a good safety and protective profile. However, there are problems of PA instability that are greatly enhanced when using aluminum adjuvants. New adjuvant compositions, dry formulations and resistant to proteolysis and deamidation mutant PA forms can help to handle this issue. Devising a modern anthrax vaccine requires huge efforts.

Potential use of microarray patches for vaccine delivery in low- and middle- income countries

Microarray patches (MAPs), also referred to as microneedle patches, are a novel methodology that have the potential to overcome barriers to vaccine delivery in low- and middle-income countries (LMICs), and transform the way that vaccines are delivered within immunization programs. The World Health Organization's Initiative for Vaccine Research and its partners are working to understand how MAPs could ease vaccine delivery and increase equitable access to vaccines in LMICs. Global stakeholders have been engaged to evaluate technical, economic, and programmatic challenges; to validate assumptions where possible; and to propose areas of focus to facilitate future vaccine-MAP product development. This report summarizes those learnings.

Recent advances in microneedle composites for biomedical applications: Advanced drug delivery technologies

In the twenty-first century, microneedles based drug delivery is drawing attention worldwide in the research due to current signs of progress in the controlled release drug delivery through microneedles. The microneedles represent a promising technology to deliver therapeutic compounds into the skin for chronic complications like osteoporosis, diabetes, cancer and induction of immune responses from protein and DNA vaccines. However, the delivery of hydrophilic drugs and macromolecular agents are challenging. In this write up authors included the meticulous illustration of the chronological development of fabrication of microneedles with respect to an assortment of techniques, their modifications, clinical trials and regulatory perspectives period of 2000-2019. This review summarizes characterization, fabrications, biological applications and challenges. Additionally, relevant patents based on microneedle from USPTO) database are also highlighted.

Noninvasive vaccination against infectious diseases

The development of a successful vaccine, which should elicit a combination of humoral and cellular responses to control or prevent infections, is the first step in protecting against infectious diseases. A vaccine may protect against bacterial, fungal, parasitic, or viral infections in animal models, but to be effective in humans there are some issues that should be considered, such as the adjuvant, the route of vaccination, and the antigen-carrier system. While almost all licensed vaccines are injected such that inoculation is by far the most commonly used method, injection has several potential disadvantages, including pain, cross contamination, needlestick injury, under- or overdosing, and increased cost. It is also problematic for patients from rural areas of developing countries, who must travel to a hospital for vaccine administration. Noninvasive immunizations, including oral, intranasal, and transcutaneous administration of vaccines, can reduce or eliminate pain, reduce the cost of vaccinations, and increase their safety. Several preclinical and clinical studies as well as experience with licensed vaccines have demonstrated that noninvasive vaccine immunization activates cellular and humoral immunity, which protect against pathogen infections. Here we review the development of noninvasive immunization with vaccines based on live attenuated virus, recombinant adenovirus, inactivated virus, viral subunits, virus-like particles, DNA, RNA, and antigen expression in rice in preclinical and clinical studies. We predict that noninvasive vaccine administration will be more widely applied in the clinic in the near future.

Public perceptions and attitudes to biological risks: Saudi Arabia and regional perspectives

Saudi Arabia has experienced frequent occurrences of biological disasters due to a wide range of generator factors, including natural disasters and epidemics. A national survey (n=1,164) was conducted across 13 regions of Saudi Arabia to examine public perceptions to the risk of a biological disaster. The primary results reveal: (a) a degree of knowledge about biological threats such as SARS and H5N1 flu, despite the lack of individual experience with disasters; (b) age, gender, education and faith are positively related to the perception of biological risk; and (c) a number of important community resilience factors exist, including faith, education and willingness. This study concludes that the development of adapted resilience strategies in disaster management can be achieved through public education and training involving cooperation with official organisations and religious authorities in the country to increase public awareness, knowledge and skills in mitigating biological threats.

The success of microneedle-mediated vaccine delivery into skin

Microneedles (MNs) are designed to specifically target the outermost, skin barrier layer, the stratum corneum, creating transient pathways for minimally invasive transcutaneous delivery. It is reported that MNs can facilitate delivery without stimulating the pain receptors or damaging blood vessels that lie beneath, thus being perceived as painless and associated with reduced bleeding. This immunocompetence of the skin, coupled with its ease of access, makes this organ an attractive vaccination site. The purpose of this review was to collate primary scientific literature pertaining to MN-mediated in vivo vaccination programmes. A total of 62 original research articles are presented, compiling vaccination strategies in 6 different models (mouse, rat, guinea pig, rabbit, pig, macaque and human). Vaccines tested span a wide range of viral, bacterial and protozoan pathogens and includes 7 of the 13 vaccine-preventable diseases, as defined by the WHO. This review highlights the paucity of available clinical trial data. MN-delivered vaccines have demonstrated safety and immunogenicity in pre-clinical models and boast desirable attributes such as painless administration, thermostability, dose-sparing capacity and the potential for self-administration. These advantages should contribute to enhanced global vaccine access.

Microneedle patches for vaccination in developing countries

Millions of people die of infectious diseases each year, mostly in developing countries, which could largely be prevented by the use of vaccines. While immunization rates have risen since the introduction of the Expanded Program on Immunization (EPI), there remain major challenges to more effective vaccination in developing countries. As a possible solution, microneedle patches containing an array of micron-sized needles on an adhesive backing have been developed to be used for vaccine delivery to the skin. These microneedle patches can be easily and painlessly applied by pressing against the skin and, in some designs, do not leave behind sharps waste. The patches are single-dose, do not require reconstitution, are easy to administer, have reduced size to simplify storage, transportation and waste disposal, and offer the possibility of improved vaccine immunogenicity, dose sparing and thermostability. This review summarizes vaccination challenges in developing countries and discusses advantages that microneedle patches offer for vaccination to address these challenges. We conclude that microneedle patches offer a powerful new technology that can enable more effective vaccination in developing countries.

Effect of vaccine administration modality on immunogenicity and efficacy

The many factors impacting the efficacy of a vaccine can be broadly divided into three categories: features of the vaccine itself, including immunogen design, vaccine type, formulation, adjuvant and dosing; individual variations among vaccine recipients and vaccine administration-related parameters. While much literature exists related to vaccines, and recently systems biology has started to dissect the impact of individual subject variation on vaccine efficacy, few studies have focused on the role of vaccine administration-related parameters on vaccine efficacy. Parenteral and mucosal vaccinations are traditional approaches for licensed vaccines; novel vaccine delivery approaches, including needless injection and adjuvant formulations, are being developed to further improve vaccine safety and efficacy. This review provides a brief summary of vaccine administration-related factors, including vaccination approach, delivery route and method of administration, to gain a better understanding of their potential impact on the safety and immunogenicity of candidate vaccines.

Intradermal vaccination using the novel microneedle device MicronJet600: Past, present, and future

Intradermal immunization has become a forefront of vaccine improvement, both scientifically and commercially. Newer technologies are being developed to address the need to reduce the dose required for vaccination and to improve the reliability and ease of injection, which have been major hurdles in expanding the number of approved vaccines using this route of administration. In this review, 7 y of clinical experience with a novel intradermal delivery device, the MicronJet600, which is a registered hollow microneedle that simplifies the delivery of liquid vaccines, are summarized. This device has demonstrated both significant dose-sparing and superior immunogenicity in various vaccine categories, as well as in diverse subject populations and age groups. These studies have shown that intradermal delivery using this device is safe, effective, and preferred by the subjects. Comparison with other intradermal devices and potential new applications for intradermal delivery that could be pursued in the future are also discussed.

The role of microneedles for drug and vaccine delivery

INTRODUCTION

Transdermal drug delivery offers a number of advantages for the patient, not only due to its non-invasive and convenient nature, but also due to factors such as avoidance of first-pass metabolism and prevention of gastrointestinal degradation. It has been demonstrated that microneedles (MNs) can increase the number of compounds amenable to transdermal delivery by penetrating the skin's protective barrier, the stratum corneum, and creating a pathway for drug permeation to the dermal tissue below.

AREAS COVERED

MNs have been extensively investigated for drug and vaccine delivery. The different types of MN arrays and their delivery capabilities are discussed in terms of drugs, including biopharmaceutics and vaccines. Patient usage and effects on the skin are also considered.

EXPERT OPINION

MN research and development is now at the stage where commercialisation is a viable possibility. There are a number of long-term safety questions relating to patient usage which will need to be addressed moving forward. Regulatory guidance is awaited to direct the scale-up of the manufacturing process alongside provision of clearer patient instruction for safe and effective use of MN devices.

Dynamic visualization of dendritic cell-antigen interactions in the skin following transcutaneous immunization

Delivery of vaccines into the skin provides many advantages over traditional parenteral vaccination and is a promising approach due to the abundance of antigen presenting cells (APC) residing in the skin including Langerhans cells (LC) and dermal dendritic cells (DDC). However, the main obstacle for transcutaneous immunization (TCI) is the effective delivery of the vaccine through the stratum corneum (SC) barrier to the APC in the deeper skin layers. This study therefore utilized microneedles (MN) and a lipid-based colloidal delivery system (cubosomes) as a synergistic approach for the delivery of vaccines to APC in the skin. The process of vaccine uptake and recruitment by specific types of skin APC was investigated in real-time over 4 hours in B6.Cg-Tg (Itgax-EYFP) 1 Mnz/J mice by two-photon microscopy. Incorporation of the vaccine into a particulate delivery system and the use of MN preferentially increased vaccine antigen uptake by a highly motile subpopulation of skin APC known as CD207⁺ DC. No uptake of antigen or any response to immunisation by LC could be detected.

Potential biological targets ofBacillus anthracisin anti-infective approaches against the threat of bioterrorism

The terrorist attacks of 2001 involving anthrax underscore the imperative that safe and effective medical countermeasures should be readily available. Vaccination appears to be the most effective form of mass protection against a biological attack, but the current vaccines have drawbacks that justify the enormous amount of effort currently being put into developing more effective vaccines and other treatment modalities. After providing a comprehensive overview of the organism Bacillus anthracis as a biological weapon and its pathogenicity, this review briefly summarizes the current knowledge vital to the management of anthrax disease. This knowledge has been acquired since 2001 as a result of the progress on anthrax research and focuses on the possible development of improved human anti-infective strategies targeting B. anthracis spore components, as well as strategies based on host-pathogen interactions.

Microneedles for intradermal and transdermal drug delivery

The formidable barrier properties of the uppermost layer of the skin, the stratum corneum, impose significant limitations for successful systemic delivery of broad range of therapeutic molecules particularly macromolecules and genetic material. Microneedle (MN) has been proposed as a strategy to breach the stratum corneum barrier function in order to facilitate effective transport of molecules across the skin. This strategy involves use of micron sized needles fabricated of different materials and geometries to create transient aqueous conduits across the skin. MN, alone or with other enhancing strategies, has been demonstrated to dramatically enhance the skin permeability of numerous therapeutic molecules including biopharmaceuticals either in vitro, ex vivo or in vivo experiments. This suggested the promising use of MN technology for various possible clinical applications such as insulin delivery, transcutaneous immunisations and cutaneous gene delivery. MN has been proved as minimally invasive and painless in human subjects. This review article focuses on recent and future developments for MN technology including the latest type of MN design, challenges and strategies in MNs development as well as potential safety aspects based on comprehensive literature review pertaining to MN studies to date.

Microneedle patches for vaccine delivery

In today's medical industry, the range of vaccines that exist for administration in humans represents an eclectic variety of forms and immunologic mechanisms. Namely, these are the live attenuated viruses, inactivated viruses, subunit proteins, and virus-like particles for treating virus-caused diseases, as well as the bacterial-based polysaccharide, protein, and conjugated vaccines. Currently, a new approach to vaccination is being investigated with the concept of DNA vaccines. As an alternative delivery route to enhance the vaccination efficacy, microneedles have been devised to target the rich network of immunologic antigen-presenting cells in the dermis and epidermis layers under the skin. Numerous studies have outlined the parameters of microneedle delivery of a wide range of vaccines, revealing comparable or higher immunogenicity to conventional intramuscular routes, overall level of stability, and dose-sparing advantages. Furthermore, recent mechanism studies have begun to successfully elucidate the biological mechanisms behind microneedle vaccination. This paper describes the current status of microneedle vaccine research.

Microarrays and microneedle arrays for delivery of peptides, proteins, vaccines and other applications

INTRODUCTION

Peptide and protein microarray and microneedle array technology provides direct information on protein function and potential drug targets in drug discovery and delivery. Because of this unique ability, these arrays are well suited for protein profiling, drug target identification/validation and studies of protein interaction, biochemical activity, immune responses, clinical prognosis and diagnosis and for gene, protein and drug delivery.

AREAS COVERED

The aim of this review is to describe and summarize past and recent developments of microarrays in their construction, characterization and production and applications of microneedles in drug delivery. The scope and limitations of various technologies in this respect are discussed.

EXPERT OPINION

This article offers a review of microarray/microneedle technologies and possible future directions in targeting and in the delivery of pharmacologically active compounds for unmet needs in biopharmaceutical research. A better understanding of the production and use of microarrays and microneedles for delivery of peptides, proteins and vaccines is needed.

Microneedles for drug and vaccine delivery

Microneedles were first conceptualized for drug delivery many decades ago, but only became the subject of significant research starting in the mid-1990's when microfabrication technology enabled their manufacture as (i) solid microneedles for skin pretreatment to increase skin permeability, (ii) microneedles coated with drug that dissolves off in the skin, (iii) polymer microneedles that encapsulate drug and fully dissolve in the skin and (iv) hollow microneedles for drug infusion into the skin. As shown in more than 350 papers now published in the field, microneedles have been used to deliver a broad range of different low molecular weight drugs, biotherapeutics and vaccines, including published human studies with a number of small-molecule and protein drugs and vaccines. Influenza vaccination using a hollow microneedle is in widespread clinical use and a number of solid microneedle products are sold for cosmetic purposes. In addition to applications in the skin, microneedles have also been adapted for delivery of bioactives into the eye and into cells. Successful application of microneedles depends on device function that facilitates microneedle insertion and possible infusion into skin, skin recovery after microneedle removal, and drug stability during manufacturing, storage and delivery, and on patient outcomes, including lack of pain, skin irritation and skin infection, in addition to drug efficacy and safety. Building off a strong technology base and multiple demonstrations of successful drug delivery, microneedles are poised to advance further into clinical practice to enable better pharmaceutical therapies, vaccination and other applications.

High immunogenicity of nicotine vaccines obtained by intradermal delivery with safe adjuvants

Immunotherapy for tobacco addiction may offer a safe, alternative treatment if the immunogenicity of the current nicotine vaccines can be improved. We show here that intradermal (ID) immunization induces the production of antibody directed against nicotine (NicAb) at a much higher level than conventional intramuscular (IM) immunization. The magnitude and duration of NicAb production was further increased robustly by non-inflammatory laser vaccine adjuvant (LVA), slightly inflammatory monophosphoryl lipid A (MPL) or a combination of MPL and CpG adjuvants. Consequently, significantly fewer vaccination doses were required to attain a high level of NicAb production for an extended period of time and reduce nicotine entry into the brain in the presence of LVA, MPL or MPL/CpG adjuvant, respectively. Yet, the potency of these adjuvants to augment ID nicotine vaccine immunogenicity came at the expense of local skin reactogenicity, with LVA causing little skin reaction and MPL/CpG stimulating overt skin irritation. These observations underscore a necessity of a balance between optimal adjuvant potency and undesired local reactogenicity. In summary, our study presents a novel approach to significantly improve nicotine vaccine immunogenicity by a combination of safe cutaneous vaccine adjuvants with ID immunization.

Microneedle and mucosal delivery of influenza vaccines

In recent years with the threat of pandemic influenza and other public health needs, alternative vaccination methods other than intramuscular immunization have received great attention. The skin and mucosal surfaces are attractive sites probably because of both noninvasive access to the vaccine delivery and unique immunological responses. Intradermal vaccines using a microinjection system (BD Soluvia(TM)) and intranasal vaccines (FluMist®) are licensed. As a new vaccination method, solid microneedles have been developed using a simple device that may be suitable for self-administration. Because coated microneedle influenza vaccines are administered in the solid state, developing formulations maintaining the stability of influenza vaccines is an important issue to be considered. Marketable microneedle devices and clinical trials remain to be developed. Other alternative mucosal routes such as oral and intranasal delivery systems are also attractive for inducing cross-protective mucosal immunity, but effective non-live mucosal vaccines remain to be developed.

Measles vaccination using a microneedle patch

Measles vaccination programs would benefit from delivery methods that decrease cost, simplify logistics, and increase safety. Conventional subcutaneous injection is limited by the need for skilled healthcare professionals to reconstitute and administer injections, and by the need for safe needle handling and disposal to reduce the risk of disease transmission through needle re-use and needlestick injury. Microneedles are micron-scale, solid needles coated with a dry formulation of vaccine that dissolves in the skin within minutes after patch application. By avoiding the use of hypodermic needles, vaccination using a microneedle patch could be carried out by minimally trained personnel with reduced risk of blood-borne disease transmission. The goal of this study was to evaluate measles vaccination using a microneedle patch to address some of the limitations of subcutaneous injection. Viability of vaccine virus dried onto a microneedle patch was stabilized by incorporation of the sugar, trehalose, and loss of viral titer was less than 1 log10(TCID50) after storage for at least 30 days at room temperature. Microneedle patches were then used to immunize cotton rats with the Edmonston-Zagreb measles vaccine strain. Vaccination using microneedles at doses equaling the standard human dose or one-fifth the human dose generated neutralizing antibody levels equivalent to those of a subcutaneous immunization at the same dose. These results show that measles vaccine can be stabilized on microneedles and that vaccine efficiently reconstitutes in vivo to generate a neutralizing antibody response equivalent to that generated by subcutaneous injection.

Expression of either lethal toxin or edema toxin by Bacillus anthracis is sufficient for virulence in a rabbit model of inhalational anthrax

The development of therapeutics against biothreats requires that we understand the pathogenesis of the disease in relevant animal models. The rabbit model of inhalational anthrax is an important tool in the assessment of potential therapeutics against Bacillus anthracis. We investigated the roles of B. anthracis capsule and toxins in the pathogenesis of inhalational anthrax in rabbits by comparing infection with the Ames strain versus isogenic mutants with deletions of the genes for the capsule operon (capBCADE), lethal factor (lef), edema factor (cya), or protective antigen (pagA). The absence of capsule or protective antigen (PA) resulted in complete avirulence, while the presence of either edema toxin or lethal toxin plus capsule resulted in lethality. The absence of toxin did not influence the ability of B. anthracis to traffic to draining lymph nodes, but systemic dissemination required the presence of at least one of the toxins. Histopathology studies demonstrated minimal differences among lethal wild-type and single toxin mutant strains. When rabbits were coinfected with the Ames strain and the PA- mutant strain, the toxin produced by the Ames strain was not able to promote dissemination of the PA- mutant, suggesting that toxigenic action occurs in close proximity to secreting bacteria. Taken together, these findings suggest that a major role for toxins in the pathogenesis of anthrax is to enable the organism to overcome innate host effector mechanisms locally and that much of the damage during the later stages of infection is due to the interactions of the host with the massive bacterial burden.

Microneedle-mediated vaccine delivery: harnessing cutaneous immunobiology to improve efficacy

INTRODUCTION

Breaching the skin's stratum corneum barrier raises the possibility of the administration of vaccines, gene vectors, antibodies and even nanoparticles, all of which have at least their initial effect on populations of skin cells.

AREAS COVERED

Intradermal vaccine delivery holds enormous potential for improved therapeutic outcomes for patients, particularly those in the developing world. Various vaccine-delivery strategies have been employed, which are discussed in this review. The importance of cutaneous immunobiology on the effect produced by microneedle-mediated intradermal vaccination is also discussed.

EXPERT OPINION

Microneedle-mediated vaccines hold enormous potential for patient benefit. However, in order for microneedle vaccine strategies to fulfill their potential, the proportion of an immune response that is due to the local action of delivered vaccines on skin antigen-presenting cells, and what is due to a systemic effect from vaccines reaching the systemic circulation, must be determined. Moreover, industry will need to invest significantly in new equipment and instrumentation in order to mass-produce microneedle vaccines consistently. Finally, microneedles will need to demonstrate consistent dose delivery across patient groups and match this to reliable immune responses before they will replace tried-and-tested needle-and-syringe-based approaches.

Intradermal immunization with outer membrane protein 25 protects Balb/c mice from virulent B. abortus 544

Brucella abortus is a causative agent of brucellosis, a zoonosis affecting the endemic areas, which infects domestic animals as well as humans, thus, posing a potential bioterror threat. Outer membrane protein 25 is conserved among the Brucella species. Omp25 mutant strain of Brucella is shown to be attenuated in mice emphasizing on the role of Omp25 in Brucella virulence. Moreover, Omp25 has been shown to inhibit TNF-α production in human macrophages, thereby, abrogating cell mediated immunity. In this study, we evaluated the immunogenic potential of recombinant Omp25 and its protective efficacy against virulent B. abortus challenge in Balb/c mice. Recombinant Omp25 was administered via two routes of immunization: intraperitoneal and intradermal. Dosage reduction was observed with intradermal immunization when compared with intraperitoneal immunization. A higher IgG1:IgG2b ratio suggested a strong Th2 bias of immune response in both the routes of immunization. In vitro stimulation of splenocytes from immunized mice resulted in high level of IL-4 along with increasing levels of IL-12 and IFN-γ indicating a mixed Th1 and Th2 type of immune response. Immunized mice were challenged with virulent B. abortus and splenic colonization of B. abortus reduced significantly in intradermally immunized mice. Intradermal immunization gave protection comparable to that of B. abortus S-19 strain. Cytokine levels in spleen homogenate after challenge revealed a cell mediated immune response with elevated levels of IL-12 and IFN-γ but no detectable amount of IL-4. This can be a possible reason behind the protection observed in mice after rOmp25 immunization. Thus, our study proposes recombinant Omp25 to be a potential subunit vaccine candidate against brucellosis.

Laser vaccine adjuvant for cutaneous immunization

Simple and efficient technologies for intradermal immunization have recently been developed, making cutaneous vaccination a valid alternative for vaccine delivery. This raises an urgent need for safe and potent adjuvants suitable for cutaneous vaccination. Many traditional adjuvants like aluminum-based adjuvants may not be appropriate for boosting cutaneous immunization because they evoke strong and persistent inflammation in the skin that would potentially breach its integrity with serious consequences. Laser vaccine adjuvant is induced by brief illumination of a small area of the skin with a safe, noninvasive laser prior to intradermal injection of the vaccine into the site of illumination. It does not stimulate overt inflammation or reactogenicity in the skin and boosts immune responses via enhancing the motility of antigen-presenting cells. Laser vaccine adjuvant is convenient, safe and ideal for augmentation of cutaneous immunization and has distinct advantages over conventional adjuvants, in particular when encountering vaccine shortages during an unpredictable event.

Immunogenomics and systems biology of vaccines

Vaccines represent a potent tool to prevent or contain infectious diseases with high morbidity or mortality. However, despite their widespread use, we still have a limited understanding of the mechanisms underlying the effective elicitation of protective immune responses by vaccines. Recent research suggests that this represents the cooperative action of the innate and adaptive immune systems. Immunity is made of a multifaceted set of integrated responses involving a dynamic interaction of thousands of molecules, whose list is constantly updated to fill the several empty spaces of this puzzle. The recent development of new technologies and computational tools permits the comprehensive and quantitative analysis of the interactions between all of the components of immunity over time. Here, we review the role of the innate immunity in the host response to vaccine antigens and the potential of systems biology in providing relevant and novel insights in the mechanisms of action of vaccines to improve their design and effectiveness.

Permeation of antigen protein-conjugated nanoparticles and live bacteria through microneedle-treated mouse skin

Background:

The present study was designed to evaluate the extent to which pretreatment with microneedles can enhance skin permeation of nanoparticles in vitro and in vivo. Permeation of live bacteria, which are physically nanoparticles or microparticles, through mouse skin pretreated with microneedles was also studied to evaluate the potential risk of microbial infection.

Methods and results:

It was found that pretreatment of mouse skin with microneedles allowed permeation of solid lipid nanoparticles, size 230 nm, with ovalbumin conjugated on their surface. Transcutaneous immunization in a mouse skin area pretreated with microneedles with ovalbumin nanoparticles induced a stronger antiovalbumin antibody response than using ovalbumin alone. The dose of ovalbumin antigen determined whether microneedle-mediated transcutaneous immunization with ovalbumin nanoparticles induced a stronger immune response than subcutaneous injection of the same ovalbumin nanoparticles. Microneedle treatment permitted skin permeation of live Escherichia coli, but the extent of the permeation was not greater than that enabled by hypodermic injection.

Conclusion:

Transcutaneous immunization on a microneedle-treated skin area with antigens carried by nanoparticles can potentially induce a strong immune response, and the risk of bacterial infection associated with microneedle treatment is no greater than that with a hypodermic injection.