Transcutaneous immunization with bacterial ADP-ribosylating exotoxins, subunits, and unrelated adjuvants

Immunomodulatory regulation by heat-labile enterotoxins and potential therapeutic applications

Introduction: Heat-labile enterotoxins (HLTs) and their cognate ganglioside receptors have been extensively studied because of their therapeutic potential. Gangliosides play arole in modulating effector cells of the immune system, and HLTs provide a novel means for stimulating ganglioside-mediated responses in immunocompetent cells.Areas covered: To evaluate the mechanisms of HLT adjuvanticity, a systemic literature review was performed using relevant keyword searches of the PubMed database, accessing literature published as recently as late 2020. Since HLTs bind to specific ganglioside receptors on immunocytes, they can act as regulators via stimulation or tapering of immune responses from associated signal transduction events. Binding of HLTs to gangliosides can increase proliferation of T-cells, increase cytokine release, augment mucosal/systemic antibody responses, and increase the effectiveness of antigen presenting cells. Subunit components also independently stimulate certain immune responses. Mutant forms of HLTs have potent immunomodulatory effects without the toxicity associated with holotoxins.Expert opinion: HLTs have been the subject of abundant research exploring their use as vaccine adjuvants, in the treatment of autoimmune conditions, in cancer therapy, and for weight loss, proving that these molecules are promising tools in the field of immunotherapy.

Transcutaneous Administration of Dengue Vaccines

In the present study, we evaluated the immunological responses induced by dengue vaccines under experimental conditions after delivery via a transcutaneous (TC) route. Vaccines against type 2 Dengue virus particles (DENV2 New Guinea C (NGC) strain) combined with enterotoxigenic Escherichia coli (ETEC) heat-labile toxin (LT) were administered to BALB/c mice in a three-dose immunization regimen via the TC route. As a control for the parenteral administration route, other mouse groups were immunized with the same vaccine formulation via the intradermic (ID) route. Our results showed that mice vaccinated either via the TC or ID routes developed similar protective immunity, as measured after lethal challenges with the DENV2 NGC strain. Notably, the vaccine delivered through the TC route induced lower serum antibody (IgG) responses with regard to ID-immunized mice, particularly after the third dose. The protective immunity elicited in TC-immunized mice was attributed to different antigen-specific antibody properties, such as epitope specificity and IgG subclass responses, and cellular immune responses, as determined by cytokine secretion profiles. Altogether, the results of the present study demonstrate the immunogenicity and protective properties of a dengue vaccine delivered through the TC route and offer perspectives for future clinical applications.

Evaluation of transcutaneous immunization as a delivery route for an enterotoxigenic E. coli adhesin-based vaccine with CfaE, the colonization factor antigen 1 (CFA/I) tip adhesin

dscCfaE is a recombinant form of the CFA/I tip adhesin CfaE, expressed by a large proportion of enterotoxigenic E. coli (ETEC). It is highly immunogenic by the intranasal route in mice and Aotus nancymaae, protective against challenge with CFA/I+ ETEC in an A. nancymaae challenge model, and antibodies to dscCfaE passively protect against CFA/I+ ETEC challenge in human volunteers. Here, we show that transcutaneous immunization (TCI) with dscCfaE in mice resulted in strong anti-CfaE IgG serum responses, with a clear dose-response effect. Co-administration with heat-labile enterotoxin (LT) resulted in enhanced immune responses over those elicited by dscCfaE alone and strong anti-LT antibody responses. The highest dose of dscCfaE administered transcutaneously with LT elicited strong HAI titers, a surrogate for the neutralization of intestinal adhesion. Fecal anti-adhesin IgG and IgA antibody responses were also induced. These findings support the feasibility of TCI for the application of an adhesin-toxin based ETEC vaccine.

Intradermal vaccination with a Pseudomonas aeruginosa vaccine adjuvanted with a mutant bacterial ADP-ribosylating enterotoxin protects against acute pneumonia

Respiratory infections are a leading cause of morbidity and mortality globally. This is partially due to a lack of effective vaccines and a clear understanding of how vaccination route and formulation influence protective immunity in mucosal tissues such as the lung. Pseudomonas aeruginosa is an opportunistic pathogen capable of causing acute pulmonary infections and is a leading cause of hospital-acquired and ventilator-associated pneumonia. With multidrug-resistant P. aeruginosa infections on the rise, the need for a vaccine against this pathogen is critical. Growing evidence suggests that a successful P. aeruginosa vaccine may require mucosal antibody and Th1- and Th17-type CD4⁺ T cells to prevent pulmonary infection. Intradermal immunization with adjuvants, such as the bacterial ADP-Ribosylating Enterotoxin Adjuvant (BARE) double mutant of E. coli heat-labile toxin (dmLT), can direct protective immune responses to mucosal tissues, including the lungs. We reasoned that intradermal immunization with P. aeruginosa outer membrane proteins (OMPs) adjuvanted with dmLT could drive neutralizing antibodies and migration of CD4⁺ T cells to the lungs and protect against P. aeruginosa pneumonia in a murine model. Here we show that mice immunized with OMPs and dmLT had significantly more antigen-specific IgG and Th1- and Th17-type CD4⁺ memory T cells in the pulmonary environment compared to control groups of mice. Furthermore, OMPs and dmLT immunized mice were significantly protected against an otherwise lethal lung infection. Protection was associated with early IFN-γ and IL-17 production in the lungs of immunized mice. These results indicate that intradermal immunization with dmLT can drive protective immunity to the lung mucosa and may be a viable vaccination strategy for a multitude of respiratory pathogens.

Novel Delivery Routes for Allergy Immunotherapy: Intralymphatic, Epicutaneous, and Intradermal

Current allergy immunotherapy protocols suffer from two main problems: long treatment duration and systemic allergic side effects of the allergen administrations. The immunologic effects of allergen administration could be enhanced and the number of allergen administrations and treatment duration reduced by choosing a tissue for administration that contains a high density of antigen-presenting cells. Local side effects could be reduced by choosing a route characterized by a low density of mast cells, and systemic side effects could be reduced by administration to nonvascularized tissues, so that inadvertent systemic distribution of the allergen and consequent systemic allergic side effects are minimized.

Comparative Adjuvant Effects of Type II Heat-Labile Enterotoxins in Combination with Two Different Candidate Ricin Toxin Vaccine Antigens

Type II heat-labile enterotoxins (HLTs) constitute a promising set of adjuvants that have been shown to enhance humoral and cellular immune responses when coadministered with an array of different proteins, including several pathogen-associated antigens. However, the adjuvant activities of the four best-studied HLTs, LT-IIa, LT-IIb, LT-IIb(T13I), and LT-IIc, have never been compared side by side. We therefore conducted immunization studies in which LT-IIa, LT-IIb, LT-IIb(T13I), and LT-IIc were coadministered by the intradermal route to mice with two clinically relevant protein subunit vaccine antigens derived from the enzymatic A subunit (RTA) of ricin toxin, RiVax and RVEc. The HLTs were tested with low and high doses of antigen and were assessed for their abilities to stimulate antigen-specific serum IgG titers, ricin toxin-neutralizing activity (TNA), and protective immunity. We found that all four HLTs tested were effective adjuvants when coadministered with RiVax or RVEc. LT-IIa was of particular interest because as little as 0.03 μg when coadministered with RiVax or RVEc proved effective at augmenting ricin toxin-specific serum antibody titers with nominal evidence of local inflammation. Collectively, these results justify the need for further studies into the mechanism(s) underlying LT-IIa adjuvant activity, with the long-term goal of evaluating LT-IIa's activity in humans.

Heat-Labile Enterotoxins

Heat-labile enterotoxins (LTs) of Escherichia coli are closely related to cholera toxin (CT), which was originally discovered in 1959 in culture filtrates of the gram-negative bacterium Vibrio cholerae. Several other gram-negative bacteria also produce enterotoxins related to CT and LTs, and together these toxins form the V. cholerae-E. coli family of LTs. Strains of E. coli causing a cholera-like disease were designated enterotoxigenic E. coli (ETEC) strains. The majority of LTI genes (elt) are located on large, self-transmissible or mobilizable plasmids, although there are instances of LTI genes being located on chromosomes or carried by a lysogenic phage. The stoichiometry of A and B subunits in holotoxin requires the production of five B monomers for every A subunit. One proposed mechanism is a more efficient ribosome binding site for the B gene than for the A gene, increasing the rate of initiation of translation of the B gene independently from A gene translation. The three-dimensional crystal structures of representative members of the LT family (CT, LTpI, and LTIIb) have all been determined by X-ray crystallography and found to be highly similar. Site-directed mutagenesis has identified many residues in the CT and LT A subunits, including His44, Val53, Ser63, Val97, Glu110, and Glu112, that are critical for the structures and enzymatic activities of these enterotoxins. For the enzymatically active A1 fragment to reach its substrate, receptor-bound holotoxin must gain access to the cytosol of target cells.

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.

Animal models for cutaneous vaccine delivery

Main challenges in skin vaccination are overcoming the stratum corneum (SC) barrier and targeting the antigen presenting cells (APC) in the epidermis and the dermis. For this purpose many delivery techniques are being developed. In vivo immunogenicity and safety studies in animals are mandatory before moving to clinical trials. However, the results obtained in animals may or may not be predictive for humans. Knowledge about differences and similarities in skin architecture and immunology within a species and between species is crucial. In this review, we discuss variables, including skin morphology, skin barrier function, mechanical properties, site of application and immunology, which should be taken into account when designing animal studies for vaccination via the skin in order to support the translation to clinical trial outcomes.

Immunostimulant patches containing Escherichia coli LT enhance immune responses to DNA- and recombinant protein-based Alzheimer's disease vaccines

Immunotherapeutic approaches to treating Alzheimer's disease (AD) using vaccination strategies must overcome the obstacle of achieving adequate responses to vaccination in the elderly. Here we demonstrate for the first time that application of the Escherichia coli heat-labile enterotoxin adjuvant-laden immunostimulatory patches (LT-IS) dramatically enhances the onset and magnitude of immune responses to DNA- and protein-based vaccines for Alzheimer's disease following intradermal immunization via gene gun and conventional needles, respectively. Our studies suggest that the immune activation mediated by LT-IS offers improved potency for generating AD-specific vaccination responses that should be investigated as an adjuvant in the clinical arena.

A nonadjuvanted transcutaneous tetanus patch is effective in boosting anti-tetanus toxoid immune responses

Dry tetanus toxoid (TTx) patches were formulated without any adjuvant, with excipients to impart antigen stabilization and to enhance skin delivery. The booster effects of the TTx patches were assessed using a guinea pig model. The study revealed significant rises in TTx IgG titers induced by the TTx patches after a low-dose subcutaneous (s.c.) prime with TTx adsorbed to aluminum hydroxide. The TTx patch can therefore be considered an effective alternative to a subcutaneous booster.

Epicutaneous Immunotherapy for Aeroallergen and Food Allergy

IgE-mediated allergies today affect up to 30 % of the population in industrialized countries. Allergen immunotherapy is the only disease-modifying treatment option with a long-term effect. However, very few patients (<5 %) choose immunotherapy, due to the long treatment duration (between 3-5 years) and possible local and systemic allergic side effects of the allergen administrations. The latter occur when an allergen accidentally reaches the blood circulation. Therefore, the ideal application route for allergen immunotherapy should be characterized by two hallmarks: firstly, by a high number of potent antigen-presenting cells, which enhance efficacy and thus shorten treatment duration. Secondly, the allergen administration site is ideally non-vascularized, so that inadvertent systemic distribution of the allergen and consequent systemic allergic side effects are minimized. The epidermis contains high numbers of potent antigen-presenting Langerhans cells and, as an epithelium, is non-vascularized. Therefore, the epidermis represents an interesting administration route. Historical evidence for the clinical efficacy of epicutaneous allergy immunotherapy (EPIT) has now been strengthened by a number of recent double-blinded placebo-controlled clinical trials performed by independent groups. We review the immunological rationale, history and clinical experience with epicutaneous allergy immunotherapy.

Efficacy of a travelers' diarrhea vaccine system in travelers to India

BACKGROUND

A patch vaccine containing heat-labile toxin (LT) from enterotoxigenic Escherichia coli (ETEC) has demonstrated to be beneficial in reducing the rate and severity of travelers' diarrhea in Latin America. To evaluate the efficacy of this transdermal vaccine system in an area with a different diarrheal pathogen profile, an additional phase 2 study was conducted in European travelers to India.

METHODS

For this multicenter, randomized, double-blinded, placebo-controlled field study 723 subjects were recruited; 603 (299 LT vaccine, 304 placebo) were included in the per-protocol-population (PPP).

RESULTS

Although the LT patch induced a measurable LT immune response in recipients, it failed to protect against LT ETEC or all-cause diarrhea. In the PPP the incidence rate of diarrhea as per primary endpoint was 6.0% (18 of 299) in the vaccine group and 5.9% (18 of 304) in the placebo group. Additionally, lower than expected rates of LT ETEC diarrheas were observed in India. The vaccine delivery system frequently produced rash and pruritus at the site of application, long term hyperpigmentation persisted in a minority of LT recipients, and also few site reactions were noted in the placebo group.

CONCLUSIONS

The evaluated patch vaccine failed to satisfy mainly with respect to protective efficacy. Noninvasive prophylactic agents against travelers' diarrhea, particularly vaccines against the most frequent pathogens, thus continue to be badly needed.

Transcutaneous antigen delivery system

Transcutaneous immunization refers to the topical application of antigens onto the epidermis. Transcutaneous immunization targeting the Langerhans cells of the skin has received much attention due to its safe, needle-free, and noninvasive antigen delivery. The skin has important immunological functions with unique roles for antigen-presenting cells such as epidermal Langerhans cells and dermal dendritic cells. In recent years, novel vaccine delivery strategies have continually been developed; however, transcutaneous immunization has not yet been fully exploited due to the penetration barrier represented by the stratum corneum, which inhibits the transport of antigens and adjuvants. Herein we review recent achievements in transcutaneous immunization, focusing on the various strategies for the enhancement of antigen delivery and vaccination efficacy. [BMB Reports 2013; 46(1): 17-24]

Generation of antigen-specific immunity following systemic immunization with DNA vaccine encoding CCL25 chemokine immunoadjuvant

A significant hurdle in vaccine development for many infectious pathogens is the ability to generate appropriate immune responses at the portal of entry, namely mucosal sites. The development of vaccine approaches resulting in secretory IgA and mucosal cellular immune responses against target pathogens is of great interest and in general, requires live viral infection at mucosal sites. Using HIV-1 and influenza A antigens as models, we report here that a novel systemically administered DNA vaccination strategy utilizing co-delivery of the specific chemokine molecular adjuvant CCL25 (TECK) can produce antigen-specific immune responses at distal sites including the lung and mesenteric lymph nodes in mice. The targeted vaccines induced infiltration of cognate chemokine receptor, CCR9+/CD11c+ immune cells to the site of immunization. Furthermore, data shows enhanced IFN-λ secretion by antigen-specific CD3+/CD8+ and CD3+/CD4+ T cells, as well as elevated HIV-1-specific IgG and IgA responses in secondary lymphoid organs, peripheral blood, and importantly, at mucosal sites. These studies have significance for the development of vaccines and therapeutic strategies requiring mucosal immune responses and represent the first report of the use of plasmid co-delivery of CCL25 as part of the DNA vaccine strategy to boost systemic and mucosal immune responses following intramuscular injection.

Transcutaneous immunization: an overview of advantages, disease targets, vaccines, and delivery technologies

Skin is an immunologically active tissue composed of specialized cells and agents that capture and process antigens to confer immune protection. Transcutaneous immunization takes advantage of the skin immune network by inducing a protective immune response against topically applied antigens. This mode of vaccination presents a novel and attractive approach for needle-free immunization that is safe, noninvasive, and overcomes many of the limitations associated with needle-based administrations. In this review we will discuss the developments in the field of transcutaneous immunization in the past decade with special emphasis on disease targets and vaccine delivery technologies. We will also briefly discuss the challenges that need to be overcome to translate early laboratory successes in transcutaneous immunization into the development of effective clinical prophylactics.

Epicutaneous allergen administration: is this the future of allergen-specific immunotherapy?

IgE-mediated allergies, such as allergic rhinoconjunctivitis and asthma, have become highly prevalent, today affecting up to 30% of the population in industrialized countries. Allergen-specific immunotherapy (SIT) either subcutaneously or via the sublingual route is effective, but only few patients (<5%) choose immunotherapy, as treatment takes several years and because allergen administrations are associated with local and, in some cases, even systemic allergic side-effects because of allergen accidentally reaching the circulation. In order to resolve these two major drawbacks, the ideal application site of SIT should have two characteristics. First, it should contain a high number of potent antigen-presenting cells to enhance efficacy and shorten treatment duration. Secondly, it should be nonvascularized in order to minimize inadvertent systemic distribution of the allergen and therefore systemic allergic side-effects. The epidermis, a nonvascularized multilayer epithelium, that contains high numbers of potent antigen-presenting Langerhans cells (LC) could therefore be an interesting administration route. The present review will discuss the immunological rational, history and actual clinical experience with epicutaneous allergen-specific immunotherapy.

Topical and mucosal liposomes for vaccine delivery

Mucosal (and in minor extent transcutanous) stimulation can induce local or distant mucosa secretory IgA. Liposomes and other vesicles as mucosal and transcutaneous adjuvants are attractive alternatives to parenteral vaccination. Liposomes can be massively produced under good manufacturing practices and stored for long periods, at high antigen/vesicle mass ratios. However, their uptake by antigen-presenting cells (APC) at the inductive sites remains as a major challenge. As neurotoxicity is a major concern in intranasal delivery, complexes between archaeosomes and calcium as well as cationic liposomes complexed with plasmids encoding for antigenic proteins could safely elicit secretory and systemic antigen-specific immune responses. Oral bilosomes generate intense immune responses that remain to be tested against challenge, but the admixing with toxins or derivatives is mandatory to reduce the amount of antigen. Most of the current experimental designs, however, underestimate the mucus blanket 100- to 1000-fold thicker than a 100-nm diameter liposome, which has first to be penetrated to access the underlying M cells. Overall, designing mucoadhesive chemoenzymatic resistant liposomes, or selectively targeted to M cells, has produced less relevant results than tailoring the liposomes to make them mucus penetrating. Opposing, the nearly 10 µm thickness stratum corneum interposed between liposomes and underlying APC can be surpassed by ultradeformable liposomes (UDL), with lipid matrices that penetrate up to the limit with the viable epidermis. UDL made of phospholipids and detergents, proved to be better transfection agents than conventional liposomes and niosomes, without the toxicity of ethosomes, in the absence of classical immunomodulators.

Mucosal immunity and HIV-1 infection: applications for mucosal AIDS vaccine development

Natural transmission of human immunodeficiency virus type 1 (HIV-1) occurs through gastrointestinal and vaginal mucosa. These mucosal tissues are major reservoirs for initial HIV replication and amplification, and the sites of rapid CD4(+) T cell depletion. In both HIV-infected humans and SIV-infected macaques, massive loss of CD4(+) CCR5(+) memory T cells occurs in the gut and vaginal mucosa within the first 10-14 days of infection. Induction of local HIV-specific immune responses by vaccines may facilitate effective control of HIV or SIV replication at these sites. Vaccines that induce mucosal responses, in particular CD8(+) cytotoxic T lymphocytes (CTL), have controlled viral replication at mucosal sites and curtailed systemic dissemination. Thus, there is strong justification for development of next generation vaccines that induce mucosal immune effectors against HIV-1 including CD8(+) CTL, CD4(+) T helper cells and secretory IgA. In addition, further understanding of local innate mechanisms that impact early viral replication will greatly inform future vaccine development. In this review, we examine the current knowledge concerning mucosal AIDS vaccine development. Moreover, we propose immunization strategies that may be able to elicit an effective immune response that can protect against AIDS as well as other mucosal infections.

Adjuvanted influenza vaccine administered intradermally elicits robust long-term immune responses that confer protection from lethal challenge

Background

The respiratory illnesses caused by influenza virus can be dramatically reduced by vaccination. The current trivalent inactivated influenza vaccine is effective in eliciting systemic virus-specific antibodies sufficient to control viral replication. However, influenza protection generated after parenteral immunization could be improved by the induction of mucosal immune responses.

Methodology/Principal Findings

Transcutaneous immunization, a non-invasive vaccine delivery method, was used to investigate the quality, duration and effectiveness of the immune responses induced in the presence of inactivated influenza virus co-administered with retinoic acid or oleic acid. We observed an increased migration of dendritic cells to the draining lymph nodes after dermal vaccination. Here we demonstrate that this route of vaccine delivery in combination with certain immunomodulators can induce potent immune responses that result in long-term protective immunity. Additionally, mice vaccinated with inactivated virus in combination with retinoic acid show an enhanced sIgA antibody response, increased number of antibody secreting cells in the mucosal tissues, and protection from a higher influenza lethal dose.

Conclusions/Significance

The present study demonstrates that transdermal administration of inactivated virus in combination with immunomodulators stimulates dendritic cell migration, results in long-lived systemic and mucosal responses that confer effective protective immunity.

Transcutaneous immunization with lipid offers a new route of vaccination against Helicobacter pylori and a new candidate delivery vehicle

Needle-free methods of vaccination may allow rapid, simple and safe vaccination of large populations. Oral vaccination is the best established method but faces the hurdle of oral tolerance to the vaccine antigen. Skin-based transcutaneous immunization (TCI) offers an alternative needle-free route of vaccination that is able to induce protective immunity without the problem of oral tolerance. Helicobacter pylori is an important human pathogen associated with a number of gastrointestinal disorders, including gastritis, peptic ulcers and gastric tumors. Conventional treatments involving the use of antibiotics have a number of limitations and the development of an effective vaccine is the best long-term treatment option. A variety of experimental vaccines to Helicobacter have been reported. The paper reviewed here combines the approach of TCI with the use of a novel lipid antigen delivery system, hitherto only used for oral vaccination, to evaluate the potential for TCI for a simple vaccination strategy against Helicobacter and potentially other disease-causing organisms.

Systemic immunization with CCL27/CTACK modulates immune responses at mucosal sites in mice and macaques

Plasmid DNA is a promising vaccine platform that has been shown to be safe and able to be administered repeatedly without vector interference. Enhancing the potency of DNA vaccination through co-delivery of molecular adjuvants is one strategy currently under investigation. Here we describe the use of the novel chemokine adjuvant CCL27/CTACK to enhance immune responses to an HIV-1 or SIV antigen in mice and rhesus macaques. CCL27 has been shown to play a role in inflammatory responses through chemotaxis of CCR10+ cells, and we hypothesized that CCL27 may modulate adaptive immune responses. Immunizations in mice with HIV-1gag/CCL27 enhanced immune responses both at peripheral and, surprisingly, at mucosal sites. To confirm these findings in a large-animal model, we created optimized CCL27 and SIV antigenic plasmid constructs for rhesus macaques. 10 macaques (n=5/group) were immunized intramuscularly with 1mg/construct of antigenic plasmids+/-CCL27 with electroporation. We observed significant IFN-gamma secretion and CD8+ T-cell proliferation in peripheral blood. Interestingly, CCL27 co-immunized macaques exhibited a trend toward greater effector CD4+ T cells in the bronchiolar lavage (BAL). CCL27 co-delivery also elicited greater antigen-specific IgA at unique sites including BAL and fecal samples but not in the periphery. Future studies incorporating CCL27 as an adjuvant in vaccine or therapy models where eliciting immune responses in the lung are warranted.

Layer-by-layer-assembled multilayer films for transcutaneous drug and vaccine delivery

We describe protein- and oligonucleotide-loaded layer-by-layer (LbL)-assembled multilayer films incorporating a hydrolytically degradable polymer for transcutaneous drug or vaccine delivery. Films were constructed based on electrostatic interactions between a cationic poly(beta-amino ester) (denoted Poly-1) with a model protein antigen, ovalbumin (ova), and/or immunostimulatory CpG (cytosine-phosphate diester-guanine-rich) DNA oligonucleotide adjuvant molecules. Linear growth of nanoscale Poly-1/ova bilayers was observed. Dried ova protein-loaded films rapidly deconstructed when rehydrated in saline solutions, releasing ova as nonaggregated/nondegraded protein, suggesting that the structure of biomolecules integrated into these multilayer films is preserved during release. Using confocal fluorescence microscopy and an in vivo murine ear skin model, we demonstrated delivery of ova from LbL films into barrier-disrupted skin, uptake of the protein by skin-resident antigen-presenting cells (Langerhans cells), and transport of the antigen to the skin-draining lymph nodes. Dual incorporation of ova and CpG oligonucleotides into the nanolayers of LbL films enabled dual release of the antigen and adjuvant with distinct kinetics for each component; ova was rapidly released, while CpG was released in a relatively sustained manner. Applied as skin patches, these films delivered ova and CpG to Langerhans cells in the skin. To our knowledge, this is the first demonstration of LbL films applied for the delivery of biomolecules into skin. This approach provides a new route for storage of vaccines and other immunotherapeutics in a solid-state thin film for subsequent delivery into the immunologically rich milieu of the skin.

Sonophoresis: recent advancements and future trends

OBJECTIVES

Use of ultrasound in therapeutics and drug delivery has gained importance in recent years, evident by the increase in patents filed and new commercial devices launched. The present review discusses new advancements in sonophoretic drug delivery in the last two decades, and highlights important challenges still to be met to make this technology of more use in the alleviation of diseases.

KEY FINDINGS

Phonophoretic research often suffers from poor calibration in terms of the amount of ultrasound energy emitted, and therefore current research must focus on safety of exposure to ultrasound and miniaturization of devices in order to make this technology a commercial reality. More research is needed to identify the role of various parameters influencing sonophoresis so that the process can be optimized. Establishment of long-term safety issues, broadening the range of drugs that can be delivered through this system, and reduction in the cost of delivery are issues still to be addressed.

SUMMARY

Sonophoresis (phonophoresis) has been shown to increase skin permeability to various low and high molecular weight drugs, including insulin and heparin. However, its therapeutic value is still being evaluated. Some obstacles in transdermal sonophoresis can be overcome by combination with other physical and chemical enhancement techniques. This review describes recent advancements in equipment and devices for phonophoresis, new formulations tried in sonophoresis, synergistic effects with techniques such as chemical enhancers, iontophoresis and electroporation, as well as the growing use of ultrasound in areas such as cancer therapy, cardiovascular disorders, temporary modification of the blood-brain barrier for delivery of imaging and therapeutic agents, hormone replacement therapy, sports medicine, gene therapy and nanotechnology. This review also lists patents pertaining to the formulations and techniques used in sonophoretic drug delivery.

Transcutaneous immunization with a synthetic hexasaccharide-protein conjugate induces anti-Vibrio cholerae lipopolysaccharide responses in mice

Antibodies specific for Vibrio cholerae lipopolysaccaride (LPS) are common in humans recovering from cholera, and constitute a primary component of the vibriocidal response, a serum complement-mediated bacteriocidal response correlated with protection against cholera. In order to determine whether transcutaneous immunization (TCI) with a V. cholerae neoglycoconjugate (CHO-BSA) comprised of a synthetic terminal hexasaccharide of the O-specific polysaccharide of V. cholerae O1 (Ogawa) conjugated with bovine serum albumin (BSA) could induce anti-V. cholerae LPS and vibriocidal responses, we applied CHO-BSA transcutaneously in the presence or absence of the immune adjuvant cholera toxin (CT) to mice. Transcutaneously applied neoglycoconjugate elicited prominent V. cholerae specific LPS IgG responses in the presence of CT, but not IgM or IgA responses. CT applied on the skin induced strong IgG and IgA serum responses. TCI with neoglycoconjugate did not elicit detectable vibriocidal responses, protection in a mouse challenge assay, or stool anti-V. cholerae IgA responses, irrespective of the presence or absence of CT. Our results suggest that transcutaneously applied synthetic V. cholerae neoglycoconjugate is safe and immunogenic, but predominantly induces systemic LPS responses of the IgG isotype.

Immune modulation by adjuvants combined with diphtheria toxoid administered topically in BALB/c mice after microneedle array pretreatment

Purpose

In this study, modulation of the immune response against diphtheria toxoid (DT) by various adjuvants in transcutaneous immunization (TCI) with microneedle array pretreatment was investigated.

Methods

TCI was performed on BALB/c mice with or without microneedle array pretreatment using DT as a model antigen co-administrated with lipopolysaccharide (LPS), Quil A, CpG oligo deoxynucleotide (CpG) or cholera toxin (CT) as adjuvant. The immunogenicity was evaluated by measuring serum IgG subtype titers and neutralizing antibody titers.

Results

TCI with microneedle array pretreatment resulted in a 1,000-fold increase of DT-specific serum IgG levels as compared to TCI. The immune response was further improved by co-administration of adjuvants, showing a progressive increase in serum IgG titers when adjuvanted with LPS, Quil A, CpG and CT. IgG titers of the CT-adjuvanted group reached levels comparable to those obtained after DT-alum subcutaneous injection. The IgG1/IgG2a ratio of DT-specific antibodies decreased in the following sequence: plain DT, Quil A, CT and CpG, suggesting that the immune response was skewed towards the Th1 direction.

Conclusions

The potency and the quality of the immune response against DT administered by microneedle array mediated TCI can be modulated by co-administration of adjuvants.

Peptide-based vaccines for cancer: realizing their potential

Advances in the engineering of peptides, adjuvants and delivery systems have renewed the enthusiasm for peptide-based vaccination regimens in the setting of cancer, and there are a variety of clinical trials being conducted by pharmaceutical companies based on the use of peptides. The challenges to successful cancer immunotherapy are common to all immunotherapeutic strategies and not unique to peptide-based vaccination regimens. This review will describe the advances in the identification, design and delivery of peptides, the challenges to successful immunotherapy and will discuss potential options for the future.

Low-frequency sonophoresis: current status and future prospects

Application of ultrasound enhances skin permeability to drugs, a phenomenon referred to as sonophoresis. Significant strides have been made in sonophoresis research in recent years, especially under low-frequency conditions (20 kHz<f<100 kHz). This article reviews the mechanistic principles and current status of sonophoresis under low-frequency conditions. Several therapeutic macromolecules including insulin, low-molecular weight heparin, and vaccines have been delivered using low-frequency sonophoresis in vivo. Clinical trials have been performed with several drugs including lidocaine and cyclosporin. Novel theoretical and experimental approaches have provided insights into the mechanisms of low-frequency sonophoresis. Current understanding of these mechanisms is presented.

Transcutaneous delivery and thermostability of a dry trivalent inactivated influenza vaccine patch

A patch containing a trivalent inactivated influenza vaccine (TIV) was prepared in a dried, stabilized formulation for transcutaneous delivery. When used in a guinea pig immunogenicity model, the dry patch was as effective as a wet TIV patch in inducing serum anti-influenza IgG antibodies. When the dry TIV patch was administered with LT as an adjuvant, a robust immune response was obtained that was comparable with or better than an injected TIV vaccine. When stored sealed in a nitrogen-purged foil, the dry TIV patch was stable for 12 months, as measured by HA content, under both refrigerated and room temperature conditions. Moreover, the immunological potency of the vaccine product was not affected by long-term storage. The dry TIV patch was also thermostable against three cycles of alternating low-to-high temperatures of -20/25 and -20/40 degrees C, and under short-term temperature stress conditions. These studies indicate that the dry TIV patch product can tolerate unexpected environmental stresses that may be encountered during shipping and distribution. Because of its effectiveness in vaccine delivery and its superior thermostable characteristics, the dry TIV patch represents a major advance for needle-free influenza vaccination.

Particle-based vaccines for transcutaneous vaccination

Immunization concepts evolve with increasing knowledge of how the immune system works and the development of new vaccination methods. Traditional vaccines are made of live, attenuated, killed or fragmented pathogens. New vaccine strategies can take advantage of particulate compounds--microspheres or nanoparticles--to target antigen-presenting cells better, which must subsequently reach the secondary lymphoid organs, which are the sites of the immune response. The use of the skin as a target organ for vaccine delivery stems from the fact that immature dendritic cells (DCs), which are professional antigen-presenting cells can be found at high density in the epidermis and dermis of human or animal skin. This has led to design various methods of dermal or transcutaneous vaccination. The quality and duration of the humoral and cellular responses to vaccination depend on the appropriate targeting of antigen-presenting cells, of the vaccine dose, route of administration and use of adjuvant. In this review, we will focus on the use of micro- and nano-particles to target the skin antigen-presenting cells and will discuss recent advances in the field of transcutaneous vaccination in animal models and humans.

Transcutaneous immunization with cross-reacting material CRM(197) of diphtheria toxin boosts functional antibody levels in mice primed parenterally with adsorbed diphtheria toxoid vaccine

Transcutaneous immunization (TCI) capitalizes on the accessibility and immunocompetence of the skin, elicits protective immunity, simplifies vaccine delivery, and may be particularly advantageous when frequent boosting is required. In this study we examined the potential of TCI to boost preexisting immune responses to diphtheria in mice. The cross-reacting material (CRM(197)) of diphtheria toxin was used as the boosting antigen and was administered alone or together with either one of two commonly used mucosal adjuvants, cholera toxin (CT) and a partially detoxified mutant of heat-labile enterotoxin of Escherichia coli (LTR72). We report that TCI with CRM(197) significantly boosted preexisting immune responses elicited after parenteral priming with aluminum hydroxide-adsorbed diphtheria toxoid (DTxd) vaccine. In the presence of LTR72 as an adjuvant, toxin-neutralizing antibody titers were significantly higher than those elicited by CRM(197) alone and were comparable to the functional antibody levels induced after parenteral booster immunization with the adsorbed DTxd vaccine. Time course study showed that high levels of toxin-neutralizing antibodies persisted for at least 14 weeks after the transcutaneous boost. In addition, TCI resulted in a vigorous antigen-specific proliferative response in all groups of mice boosted with the CRM(197) protein. These findings highlight the promising prospect of using booster administrations of CRM(197) via the transcutaneous route to establish good herd immunity against diphtheria.

Transcutaneous immunization with heat-labile enterotoxin: development of a needle-free vaccine patch

The skin is an attractive target for vaccine delivery. Adjuvants and antigens delivered into the skin can result in potent immune responses and an unmatched safety profile. The heat-labile enterotoxin (LT) from Escherichia coli, which acts both as antigen and adjuvant, has been shown to be delivered to human skin efficiently when used in a patch, resulting in strong immune responses. Iomai scientists have capitalized on these observations to develop late-stage products based on LT. This has encouraged commercial-level product development of a delivery system that is efficient, user-friendly and designed to address important medical needs. Over the past 2 years, extensive clinical testing and optimization has allowed the patch to evolve to a late-stage product. As a strategy for approval of a revolutionary vaccine-delivery system, the singular focus on optimization of LT delivery has enabled technical progress to extend patch-vaccine product development beyond LT. The field efficacy of the LT-based travelers' diarrhea vaccine has validated this approach. The discussion of transcutaneous immunization is unique, in that any consideration of the adjuvant must also include delivery, and the significant advances in a commercial patch application system are described. In this review, we integrate these concepts, update the clinical data and look to the future.

Transcutaneous immunization by merely prolonging the duration of antigen presence on the skin of mice induces a potent antigen-specific antibody response even in the absence of an adjuvant

Transcutaneous immunization (TCI) is a promising needle-free technique for vaccination. In this method, strong adjuvants, such as the cholera toxin, are generally crucial to elicit a robust immune response. Here, we showed that prolonged antigen presence on the skin of mice during TCI could effectively enhance the immune response. Substantial antigen-specific antibodies were produced in the sera of mice even after non-adjuvanted TCI when the antigen presence was for longer than 16 h. This non-adjuvanted TCI method was applied using the tetanus toxoid, and potent tetanus toxoid-specific antibodies were successfully induced in the sera of mice; they survived a lethal tetanus toxin challenge with no clinical signs. Thus, non-adjuvanted approach might be a possible option for TCI, and this method might improve the safety and practicality of transcutaneous vaccination.

Topical TLR9 agonists induce more efficient cross-presentation of injected protein antigen than parenteral TLR9 agonists do

Topical application of adjuvant to the skin promotes the generation of immune responses to co-administered peptide or protein antigen. We demonstrate that topical administration of CpG adjuvant (a TLR9 agonist) induces the cross-presentation of, and antigen-specific CTL induction to, locally injected soluble protein antigen. C57BL/6 mice were immunized by subcutaneous or intramuscular injection with ovalbumin (OVA) protein as model antigen. Application of CpG to the local skin induced more efficient cross-presentation of the injected antigen than co-injected adjuvant. Robust antigen-specific CTL responses were generated, as determined by antigen-specific CTL enumeration using tetramers, IFN-gamma ELISPOT analysis and cytotoxicity assays. Long-term memory CTL responses were induced. Topical administration of adjuvant induced Langerhans cell migration, local type 1 IFN-dependent myxovirus-resistance protein A expression and bystander dendritic cell (DC) activation. Soluble antigen-bearing DC within the skin draining lymph nodes were mainly CD11chiCD11bhilangerinloDEC205lo. Topical administration did not result in the splenomegaly or systemic cytokine induction (including TNF-alpha, IL-12, IFN-gamma and MCP-1) noted with parenteral administration. Topical TLR9 family agonists may be used to modulate the immune response to soluble protein vaccines administered by standard percutaneous route. Topical adjuvant administration increases efficacy of CTL induction and reduces toxicity when compared to parenteral adjuvant administration.

Vesicular carrier constructs for topical immunisation

Topical immunisation represents a convenient and novel approach to vaccination. Skin is exploited as a route of immunisation because it shows both specific and non-specific immune responses against foreign invaders, and these responses are a result of the presence of immunocompetent cells within the skin layers. These skin-resident antigen-presenting cells are highly efficient for the initiation of humoural and cellular immune responses. Vesicular carrier systems, particularly liposomes, vesosomes, niosomes and transferosomes, have been advocated for the topical delivery of biomacromolecules. This review describes the potential and feasibility of vesicular carrier-based vaccine delivery for topical immunisation.

Transcutaneous immunization with Clostridium difficile toxoid A induces systemic and mucosal immune responses and toxin A-neutralizing antibodies in mice

Clostridium difficile is the leading cause of nosocomial infectious diarrhea. C. difficile produces two toxins (A and B), and systemic and mucosal anti-toxin A antibodies prevent or limit C. difficile-associated diarrhea. To evaluate whether transcutaneous immunization with formalin-treated C. difficile toxin A (CDA) induces systemic and mucosal anti-CDA immune responses, we transcutaneously immunized three cohorts of mice with CDA with or without immunoadjuvantative cholera toxin (CT) on days 0, 14, 28, and 42. Mice transcutaneously immunized with CDA and CT developed prominent anti-CDA and anti-CT immunoglobulin G (IgG) and IgA responses in serum and anti-CDA and anti-CT IgA responses in stool. Sera from immunized mice were able to neutralize C. difficile toxin A activity in an in vitro cell culture assay. CDA itself demonstrated adjuvant activity and enhanced both serum and stool anti-CT IgA responses. Our results suggest that transcutaneous immunization with CDA toxoid may be a feasible immunization strategy against C. difficile, an important cause of morbidity and mortality against which current preventative strategies are failing.

Initiation of adaptive immune responses by transcutaneous immunization

The development of new, effective, easy-to-use and lower-cost vaccination approaches for the combat against malignant and infectious diseases is a pre-eminent need: cancer is a leading cause of morbidity in the Western World; there are numerous pathogenic diseases for which we still have no protective or therapeutic cure; and the financial limitations of developing countries to fight these diseases. In this mini-review we focus on transcutaneous immunization (TCI), a relatively new route for antigen delivery. TCI protocols appear to be particularly promising by gaining access to skin resident APC, which are highly efficient for the initiation of humoral and/or cellular immune responses. Consisting of an adjuvant as a stimulus in combination with an antigen which defines the target, TCI offers a most attractive immunization strategy to mount highly specific full-blown adaptive immune responses. As a topically applicable cell-free adjuvant/antigen mixture, TCI might be suitable to improve patient compliance, as well as feasible economically for the use in Third World countries. In addition, this non-invasive procedure might increase the safety of vaccinations by eliminating the risk of infections related to the recycling and improper disposal of needles. The dissection of antigen and adjuvant is important because it allows "free" combinations in contrast to classical immunizations which are based on application of the pathogen of interest. The most relevant ways and means to find new, effective pathogenic target antigens are "reverse vaccinology" and the direct peptide-epitope identification from MHC molecules with mass-spectrometry. Due to these efficient approaches the variety of antigenic epitopes for potential protective/therapeutic use is perpetually expanding. The most studied adjuvants in TCI approaches are cholera toxin (CT) and its less toxic relative, the heat-labile enterotoxin (LT). Both CT and LT can serve as antigen as well. In contrast to these large proteins, which can only penetrate "pre-treated" skin barrier, the immune response modifier, TLR7 agonist R-837 (Imiquimod) is a small compound adjuvant that easily passages non-disrupted epidermis. It remains currently elusive which cells of the complex-structured "skin-associated lymphoid tissue" (SALT) respond to the adjuvant and which APC carries the antigen to the draining lymphnodes for subsequent initiation of adaptive immune responses.

Topical vaccination: the skin as a unique portal to adaptive immune responses

Skin is an ideal tissue for vaccine administration, as it is comprised of immunocompetent cells such as keratinocytes and Langerhans cells and elicits both innate and adaptive immune responses. In this paper, we summarize the immune responses induced by topical vaccination of the skin and review the effects of adjuvants on skin vaccination. We also summarize the existing techniques for skin vaccination. New techniques such as the use of lasers to enhance skin permeability are also discussed, as well as the role of the stratum corneum in skin vaccination. A recent study demonstrating enhanced skin vaccination by using surfactants to extract partial lamellar lipids of the stratum corneum will also be introduced in this review.