Epidermal powder immunization with a recombinant HIV gp120 targets Langerhans cells and induces enhanced immune responses

Microarray patches: scratching the surface of vaccine delivery

INTRODUCTION

Microneedles are emerging as a promising technology for vaccine delivery, with numerous advantages over traditional needle and syringe methods. Preclinical studies have demonstrated the effectiveness of MAPs in inducing robust immune responses over traditional needle and syringe methods, with extensive studies using vaccines targeted against different pathogens in various animal models. Critically, the clinical trials have demonstrated safety, immunogenicity, and patient acceptance for MAP-based vaccines against influenza, measles, rubella, and SARS-CoV-2.

AREAS COVERED

This review provides a comprehensive overview of the different types of microarray patches (MAPs) and analyses of their applications in preclinical and clinical vaccine delivery settings. This review also covers additional considerations for microneedle-based vaccination, including adjuvants that are compatible with MAPs, patient safety and factors for global vaccination campaigns.

EXPERT OPINION

MAP vaccine delivery can potentially be a game-changer for vaccine distribution and coverage in both high-income and low- and middle-income countries. For MAPs to reach this full potential, many critical hurdles must be overcome, such as large-scale production, regulatory compliance, and adoption by global health authorities. However, given the considerable strides made in recent years by MAP developers, it may be possible to see the first MAP-based vaccines in use within the next 5 years.

Recent insights into cutaneous immunization: How to vaccinate via the skin

Technologies and strategies for cutaneous vaccination have been evolving significantly during the past decades. Today, there is evidence for increased efficacy of cutaneously delivered vaccines allowing for dose reduction and providing a minimally invasive alternative to traditional vaccination. Considerable progress has been made within the field of well-established cutaneous vaccination strategies: Jet and powder injection technologies, microneedles, microporation technologies, electroporation, sonoporation, and also transdermal and transfollicular vaccine delivery. Due to recent advances, the use of cutaneous vaccination can be expanded from prophylactic vaccination for infectious diseases into therapeutic vaccination for both infectious and non-infectious chronic conditions. This review will provide an insight into immunological processes occurring in the skin and introduce the key innovations of cutaneous vaccination technologies.

Intradermal powder immunization with protein-containing vaccines

The central importance for global public health policy of delivering life-saving vaccines for all children makes the development of efficacious and safe needle-free alternatives to hypodermic needles, preferably in a thermostable form, a matter of pressing urgency. This paper comprehensively reviews past in vivo studies on intradermal powder immunization with vaccine formulations that do not require refrigeration. Particular emphasis is given to the immune response in relation to antigen adjuvantation. While needle-free intradermal delivery of vaccines induces a predominantly Th2-type immune response, adjuvants powerfully enhance and modulate the magnitude and nature of the elicited immune response at various effector sites.

Transcutaneous vaccines--current and emerging strategies

INTRODUCTION

Vaccination, which is the major fundamental prophylaxis against illness and death from infectious disease, has greatly contributed to the global improvement of human health. However, the disadvantages of conventional injection systems hamper the delivery of vaccination technologies to developing countries. The imminent practice of easy-to-use vaccination methods is expected to overcome certain issues associated with injectable vaccinations. One innovative method is the transcutaneous immunization (TCI) system.

AREAS COVERED

Two major strategies for TCI are discussed in this review. One is to promote antigen permeation of the skin barrier by patch systems or nanoparticles. The other is the delivery of antigens into the skin by electroporation and microneedles in order to physically overcome the skin barrier. Moreover, adjuvant development for TCI is discussed.

EXPERT OPINION

Many different approaches have been developed for TCI, which have the potential to be effective, easy-to-use and painless methods of vaccination. However, in practical terms, the guidelines concerning the manufacturing processes and clinical trial evaluation of the procedures have not kept pace with the development of these novel formulations. The accumulation of information regarding skin characteristics and the properties of TCI devices will help refine TCI system development guidelines and thus lead to the improvement of transcutaneous vaccination.

Gold nanoparticles in biomedical applications: recent advances and perspectives

Gold nanoparticles (GNPs) with controlled geometrical, optical, and surface chemical properties are the subject of intensive studies and applications in biology and medicine. To date, the ever increasing diversity of published examples has included genomics and biosensorics, immunoassays and clinical chemistry, photothermolysis of cancer cells and tumors, targeted delivery of drugs and antigens, and optical bioimaging of cells and tissues with state-of-the-art nanophotonic detection systems. This critical review is focused on the application of GNP conjugates to biomedical diagnostics and analytics, photothermal and photodynamic therapies, and delivery of target molecules. Distinct from other published reviews, we present a summary of the immunological properties of GNPs. For each of the above topics, the basic principles, recent advances, and current challenges are discussed (508 references).

Delivery systems for intradermal vaccination

Intradermal (ID) vaccination can offer improved immunity and simpler logistics of delivery, but its use in medicine is limited by the need for simple, reliable methods of ID delivery. ID injection by the Mantoux technique requires special training and may not reliably target skin, but is nonetheless used currently for BCG and rabies vaccination. Scarification using a bifurcated needle was extensively used for smallpox eradication, but provides variable and inefficient delivery into the skin. Recently, ID vaccination has been simplified by introduction of a simple-to-use hollow microneedle that has been approved for ID injection of influenza vaccine in Europe. Various designs of hollow microneedles have been studied preclinically and in humans. Vaccines can also be injected into skin using needle-free devices, such as jet injection, which is receiving renewed clinical attention for ID vaccination. Projectile delivery using powder and gold particles (i.e., gene gun) have also been used clinically for ID vaccination. Building off the scarification approach, a number of preclinical studies have examined solid microneedle patches for use with vaccine coated onto metal microneedles, encapsulated within dissolving microneedles or added topically to skin after microneedle pretreatment, as well as adapting tattoo guns for ID vaccination. Finally, technologies designed to increase skin permeability in combination with a vaccine patch have been studied through the use of skin abrasion, ultrasound, electroporation, chemical enhancers, and thermal ablation. The prospects for bringing ID vaccination into more widespread clinical practice are encouraging, given the large number of technologies for ID delivery under development.

Mucosal targeting of a BoNT/A subunit vaccine adjuvanted with a mast cell activator enhances induction of BoNT/A neutralizing antibodies in rabbits

BACKGROUND

We previously reported that the immunogenicity of Hcβtre, a botulinum neurotoxin A (BoNT/A) immunogen, was enhanced by fusion to an epithelial cell binding domain, Ad2F, when nasally delivered to mice with cholera toxin (CT). This study was performed to determine if Ad2F would enhance the nasal immunogenicity of Hcβtre in rabbits, an animal model with a nasal cavity anatomy similar to humans. Since CT is not safe for human use, we also tested the adjuvant activity of compound 48/80 (C48/80), a mast cell activating compound previously determined to safely exhibit nasal adjuvant activity in mice.

METHODS

New Zealand White or Dutch Belted rabbits were nasally immunized with Hcβtre or Hcβtre-Ad2F alone or combined with CT or C48/80, and serum samples were tested for the presence of Hcβtre-specific binding (ELISA) or BoNT/A neutralizing antibodies.

RESULTS

Hcβtre-Ad2F nasally administered with CT induced serum anti-Hcβtre IgG ELISA and BoNT/A neutralizing antibody titers greater than those induced by Hcβtre + CT. C48/80 provided significant nasal adjuvant activity and induced BoNT/A-neutralizing antibodies similar to those induced by CT.

CONCLUSIONS

Ad2F enhanced the nasal immunogenicity of Hcβtre, and the mast cell activator C48/80 was an effective adjuvant for nasal immunization in rabbits, an animal model with a nasal cavity anatomy similar to that in humans.

Regulated exocytosis from astrocytes physiological and pathological related aspects

Astrocytes have traditionally been considered ancillary, satellite cells of the nervous system. However, it is a very recent acquisition that glial cells generate signaling loops which are integral to the brain circuitry and participate, interactively with neuronal networks, in the processing of information. Such a conceptual breakthrough makes this field of investigation one of the hottest in neuroscience, as it calls for a revision of past theories of brain function as well as for new strategies of experimental exploration of brain function. Glial cells are electrically not excitable, and it was only the use of optical recording techniques together with calcium sensitive dyes, that allowed the chemical excitability of glial cells to become apparent. Studies using these new techniques have shown for the first time that glial cells are activated by surrounding synaptic activity and translate neuronal signals into their own calcium code. Intracellular calcium concentration([Ca2+]i) elevations in glial cells have then shown to underlie spatial transfer of information in the glial network, accompanied by release of chemical transmitters (gliotransmitters) such as glutamate and back-signaling to neurons. As a consequence, optical imaging techniques applied to cell cultures or intact tissue have become a state-of-the-art technology for studying glial cell signaling. The molecular mechanisms leading to release of "gliotransmitters," especially glutamate, from glia are under debate. Accumulating evidence clearly indicates that astrocytes secrete numerous transmitters by Ca(2+)-dependent exocytosis. This review will discuss the mechanisms underlying the release of chemical transmitters from astrocytes with a particular emphasis to the regulated exocytosis processes.

Epidermal delivery of protein and DNA vaccines

Targeting vaccines to the skin epidermis results in the activation of an immune inductive site that is rich in antigen-presenting cells. The superficial location of the skin makes it accessible to vaccine delivery. However, it is difficult to access the epidermis using needle and syringe delivery, and vaccine antigens are too large to be effectively delivered using standard topical formulations. Needle-free vaccine delivery systems have been developed for efficient delivery of particulate vaccines into the epidermal tissue. Particle-mediated epidermal delivery of DNA vaccines is based on the delivery of DNA-coated gold particles directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Alternatively, protein vaccines can be formulated into a dense powder, which can be propelled into the skin epidermis by epidermal powder immunisation using similar delivery devices and principles, but in this instance the protein is delivered to the extracellular space. Preclinical and clinical data will be reviewed, demonstrating applications of epidermal vaccine delivery to a wide range of experimental infectious disease vaccines.

Novel peptide-based HIV-1 immunotherapy

Therapeutic immunisation of human immunodeficiency virus type 1-infected individuals should be actively pursued in the first instance to augment highly active antiretroviral therapy regimens. Peptide-based immunotherapeutic strategies offer considerable advantages over conventional approaches, particularly regarding safety. Peptide design itself is becoming increasingly sophisticated, with the rapid evolution of bioinformatics tools that can analyse not only T cell epitopes, but also their potential for successful presentation on diverse human leukocyte antigen (HLA) class I or II following intracellular processing by antigen-presenting cells (APCs). By targeting conserved viral domains, peptides acquire improved reactivity to diverse viral strains. Dendritic cells represent a powerful route of administration, as they are the most potent APCs and can present exogenous peptides on both HLA class I and II through the process of cross-presentation. In this way, soluble peptides can thereby stimulate both CD4+ and CD8+ T cells.

Influenza vaccine powder formulation development: spray-freeze-drying and stability evaluation

The purpose of this study was to develop a spray-freeze-drying (SFD) process for preparing an influenza vaccine dry powder formulation suitable for epidermal powder immunization. After preformulation of two types of flu vaccines, their dry-powder formulations were prepared by SFD. Powder properties and physical stability were determined using particle size analysis, tap density measurement, scanning electron microscopy, optical microscopy, and moisture content analysis. Chemical and biochemical stability of vaccine antigens was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, single radial immunodiffusion assay, and in vivo immunogenicity in a mouse model. We demonstrated that SFD could produce high-density particles-a critical parameter for effective skin penetration. From the stability perspective, the stress posed by SFD was mild because the antigen in the dry powder retained its stability, potency, and immunogenicity. Among several formulations screened, we noted that formulation composition has a significant role in the powder's long-term physical and biochemical stability. One formulation, in particular, containing sub-unit vaccine (45 microg of antigen in 1 mg of powder) with a tertiary mixture of trehalose, mannitol, and dextran, exhibited excellent overall stability, including acceptable biochemical stability after being exposed to a highly humid environment. After all, we have not only demonstrated the suitability of SFD to prepare powders for epidermal powder immunization but also developed a systematic formulation development strategy that allowed the optimization of an influenza vaccine dry powder formulation. More important, this study led to the selection of a formulation system that had been successfully tested in a human clinical study.

An antigen-independent but not antigen-specific T(H)1 response provides protection in the murine airway inflammation model

BACKGROUND

Atopic disorders are associated with an imbalanced T(H) cell response biased toward a strong T(H)2 type, resulting in excessive production of IgE antibodies, eosinophil recruitment and activation, and mast cell degranulation. Restoring the T(H)1-T(H)2 balance by increasing the antigen-specific T(H)1 response has been pursued for specific allergy immunotherapy. Synthetic oligodeoxynucleotides containing unmethylated CG dinucleotides (CpG) are strong T(H)1 adjuvants and are being investigated for allergy immunotherapy.

OBJECTIVE

This study was designed to investigate the protective role of antigen-specific T(H)1 responses induced by epidermal powder immunization with ovalbumin (OVA) and CpG in a murine airway inflammation model.

METHODS

An allergy model was used in which BALB/c mice were sensitized and then challenged with OVA. Mice received prophylactic or therapeutic immunizations with OVA, CpG, or both. After challenge, pulmonary inflammation and cell infiltration were measured on the basis of BAL cell counts and lung histology. Immune response was determined by measuring the levels of lavage cytokines and serum antibodies.

RESULTS

Coadministration of OVA and CpG by means of subcutaneous injection or epidermal powder immunization, although inducing a strong T(H)1 response, neither suppressed T(H)2 cytokines nor offered protection against pulmonary eosinophilia and histopathology in a mouse challenge model. However, when CpG was used as a stand-alone treatment of previously sensitized animals, protection against allergic airway inflammation was observed. After challenge with OVA, eosinophilia was suppressed in the lungs of the CpG-treated mice.

CONCLUSION

This finding argues against the approach of boosting an allergen-dependent T(H)1 response and favors induction of an antigen-independent T(H)1 response for allergy immunotherapy.

Approaches to enhance the efficacy of DNA vaccines

DNA vaccines consist of antigen-encoding bacterial plasmids that are capable of inducing antigen-specific immune responses upon inoculation into a host. This method of immunization is advantageous in terms of simplicity, adaptability, and cost of vaccine production. However, the entry of DNA vaccines and expression of antigen are subjected to physical and biochemical barriers imposed by the host. In small animals such as mice, the host-imposed impediments have not prevented DNA vaccines from inducing long-lasting, protective humoral, and cellular immune responses. In contrast, these barriers appear to be more difficult to overcome in large animals and humans. The focus of this article is to summarize the limitations of DNA vaccines and to provide a comprehensive review on the different strategies developed to enhance the efficacy of DNA vaccines. Several of these strategies, such as altering codon bias of the encoded gene, changing the cellular localization of the expressed antigen, and optimizing delivery and formulation of the plasmid, have led to improvements in DNA vaccine efficacy in large animals. However, solutions for increasing the amount of plasmid that eventually enters the nucleus and is available for transcription of the transgene still need to be found. The overall conclusions from these studies suggest that, provided these critical improvements are made, DNA vaccines may find important clinical and practical applications in the field of vaccination.

Epidermal powder immunization: cellular and molecular mechanisms for enhancing vaccine immunogenicity

Epidermal powder immunization (EPI) of mice with an influenza vaccine elicited consistently a higher hemagglutination inhibition (HI) antibody titers than intramuscular (IM) injection using the same dose of vaccine. The epidermal Langerhans cells (LCs) at the site of EPI were found to play an important role in the immune responses. Indeed, depletion of LCs from the immunization site prior to EPI caused a significant reduction in the antibody response. Transfer of LCs isolated from the EPI sites to naive mice induced a robust antigen-specific antibody response. Cytokines produced by target site cells appear to be important for the augmented immune responses induced by EPI. LTR72, a genetically detoxified heat-labile toxin from Escherichia coli with a strong adjuvant effect in EPI, was found to bind the keratinocytes of the epidermis, but not the LCs, and caused the production of elevated TNF-alpha and IL-12 cytokines in emigrating epidermal cells. These results have important implications for the development of a more efficacious human influenza vaccine.

Enhancement of vaccine potency through improved delivery

The need for more potent, safe and well-characterised vaccines has necessitated the discovery and development of new vaccine technologies. These include adjuvants to target the innate immune system to provide a stimulus that potentiates the development of an antigen-specific immune response, and delivery systems to ensure that the antigen and adjuvant are localised to the appropriate immune compartments. Several such technologies are being tested in human clinical trials and a few have been licensed for limited use in human vaccines. This review will highlight some of the promising technologies that may have an impact on how vaccines are administered.

A protective effect of epidermal powder immunization in a mouse model of equine herpesvirus-1 infection

To evaluate the protective effect of epidermal powder immunization (EPI) against equine herpesvirus-1 (EHV-1) infection, we prepared a powder vaccine in which formalin-inactivated virions were embedded in water-soluble, sugar-based particles. A PowderJect device was used to immunize mice with the powder vaccine via their abdominal skin. We found that twice-immunized mice were protected against challenge with the wild-type virus. This protective effect was equivalent to or better than that observed in mice immunized with other types of vaccines, including a gene gun-mediated DNA vaccine containing the glycoprotein D (gD) gene or conventional inactivated virus vaccines introduced via intramuscular or intranasal injections. These findings indicate that the powder vaccine is a promising approach for the immunological control of EHV-1 infection, either alone or as a part of prime-boost vaccination strategies.

Optimization of an alum-adsorbed vaccine powder formulation for epidermal powder immunization

PURPOSE

To develop stable and effective aluminum salt (alum)-adsorbed vaccine powder formulations for epidermal powder immunization (EPI) via a spray freeze-drying (SFD) process.

METHODS

Powder properties were determined using particle size analysis, tap density, and scanning electron microscopy. Alum coagulation was monitored via optical microscopy and particle sedimentation. Protein analysis was determined by the BCA protein assay, SDS-PAGE, and an enzyme immunoassay. In vivo immunogenicity and skin reactogenicity were performed on hairless guinea pigs and pigs, respectively.

RESULTS

SFD of hepatitis B surface antigen (HBsAg) adsorbed to aluminum hydroxide or aluminum phosphate using an excipient combination of trehalose/mannitol/dextran produced vaccine powders of dense particles and satisfactory powder flowability and hygroscopicity. This formulation also offered excellent long-term stability to the powder and the antigen. The two most important factors influencing alum particle coagulation are the freezing rate and the concentration of aluminum in the liquid formulation for SFD. The SFD vaccines, when delivered to hairless guinea pigs by EPI or injected intramuscularly after reconstitution, were as immunogenic as the original liquid vaccine. A further study showed that EPI with SFD alum-adsorbed diphtheria-tetanus toxoid vaccine was well tolerated, whereas needle injection of the liquid formulation caused persistent granuloma.

CONCLUSIONS

Stabilization of alum-adsorbed vaccine by SFD has important implications in extending vaccination to areas lacking a cold chain for transportation and storage and may also accelerate the development of new immunization technologies such as EPI.

Epidermal powder immunization of mice and monkeys with an influenza vaccine

Epidermal powder immunization (EPI) with an influenza vaccine and an adjuvant such as QS-21, LTR72, or cholera toxin elicited augmented serum and mucosal antibody responses in mice. Rhesus macaques, which have an immune system and skin structure similar to humans, were used to further evaluate the immunogenicity of the influenza vaccine following EPI. EPI of rhesus macaques with an influenza vaccine and QS-21 adjuvant elicited significantly higher serum hemagglutination inhibition (HI) titers than antigen alone administered by EPI or by intramuscular (IM) injection using a needle and syringe. In the absence of QS-21, EPI and IM injection elicited comparable HI titers in the monkeys. This study suggests that EPI is a promising technique for administering human vaccine and that QS-21 augments the immunogenicity of co-administered influenza vaccine.