Transcutaneous delivery of CpG-adjuvanted allergen via laser-generated micropores

Clinical perspective on topical vaccination strategies

Vaccination is one of the most successful measures in modern medicine to combat diseases, especially infectious diseases, and saves millions of lives every year. Vaccine design and development remains critical and involves many aspects, including the choice of platform, antigen, adjuvant, and route of administration. Topical vaccination, defined herein as the introduction of a vaccine to any of the three layers of the human skin, has attracted interest in recent years as an alternative vaccination approach to the conventional intramuscular administration because of its potential to be needle-free and induce a superior immune response against pathogens. In this review, we describe recent progress in developing topical vaccines, highlight progress in the development of delivery technologies for topical vaccines, discuss potential factors that might impact the topical vaccine efficacy, and provide an overview of the current clinical landscape of topical vaccines.

Recent advances in epicutaneous immunotherapy and potential applications in food allergy

Given the potent immunological properties of the skin, epicutaneous immunotherapy (EPIT) emerges as a promising treatment approach for inducing immune tolerance, particularly for food allergies. Targeting the highly immunocompetent, non-vascularized epidermis allows for the application of microgram amounts of allergen while significantly reducing the risk of allergen passage into the bloodstream, thus limiting systemic allergen exposure and distribution. This makes EPIT highly suitable for the treatment of potentially life-threatening allergies such as food allergies. Multiple approaches to EPIT are currently under investigation for the treatment of food allergy, and these include the use of allergen-coated microneedles, application of allergen on the skin pretreated by tape stripping, abrasion or laser-mediated microperforation, or the application of allergen on the intact skin using an occlusive epicutaneous system. To date, the most clinically advanced approach to EPIT is the Viaskin technology platform. Viaskin is an occlusive epicutaneous system (patch) containing dried native allergen extracts, without adjuvants, which relies on frequent application for the progressive passage of small amounts of allergen to the epidermis through occlusion of the intact skin. Numerous preclinical studies of Viaskin have demonstrated that this particular approach to EPIT can induce potent and long-lasting T-regulatory cells with broad homing capabilities, which can exert their suppressive effects in multiple organs and ameliorate immune responses from different routes of allergen exposure. Clinical trials of the Viaskin patch have studied the efficacy and safety for the treatment of life-threatening allergies in younger patients, at an age when allergic diseases start to occur. Moreover, this treatment approach is designed to provide a non-invasive therapy with no restrictions on daily activities. Taken together, the preclinical and clinical data on the use of EPIT support the continued investigation of this therapeutic approach to provide improved treatment options for patients with allergic disorders in the near future.

Innovative delivery systems for epicutaneous immunotherapy

Allergen-specific immunotherapy (AIT) describes the establishment of peripheral tolerance through repeated allergen exposure, which qualifies as the only curative treatment for allergic diseases. Although conventional subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) have been approved to treat respiratory allergies clinically, the progress made is far from satisfactory. Epicutaneous immunotherapy (EPIT) exploits the skin's immune properties to modulate immunological response, which is emerging as a promising alternative and has shown effectiveness in many preclinical and clinical studies for both respiratory and food allergies. It is worth noting that the stratum corneum (SC) barrier impedes the effective delivery of allergens, while disrupting the SC layer excessively often triggers unexpected Th2 immune responses. This work aims to comprehend the immunological mechanisms of EPIT, and summarize the innovative system for sufficient delivery of allergens as well as tolerogenic adjuvants. Finally, the safety, acceptability, and cost-effectiveness of these innovative delivery systems are discussed, which directs the development of future immunotherapies with all desirable characteristics.

Sustained antigens delivery using composite microneedles for effective epicutaneous immunotherapy

Allergen-specific immunotherapy (SIT) is a desirable way of therapy for various allergic diseases such as food allergy (FA). However, frequent visits for more than 3 years and potential adverse effects often hinder patient compliance. Recently, many researchers started focusing on microneedles (MNs) as a new method for SIT. In this study, we proposed an implantable MNs system produced by a two-step casting process, consisting of OVA (antigen)-loaded silk microneedles and a dissolvable, flexible polyvinyl alcohol (PVA) pedestal. Different from PVA, silk fibroin hydrogel has preferable vaccine release ability in vivo and in vitro. Once MNs are inserted into the skin, the PVA pedestal can dissolve in the interstitial fluid of the excised skin within 5 min and implant the OVA-loaded silk microneedle tips in dermal layer as a sustained antigen depot, thus inducing long-lasting immune response for at least 2 weeks. After receiving 3 doses of MN-based immunotherapy, the immune response in OVA-sensitized mice was successfully suppressed, with no apparent side effects. Compared to conventional subcutaneous immunotherapy (total dose of 150 [Formula: see text]g), MN immunotherapy ameliorated systemic anaphylaxis more effectively even at a lower dose (total dose of 30 [Formula: see text]g), demonstrating the antigen dose-sparing potential of the proposed MNs. Moreover, due to the prolonged release effect of silk-PVA composite MNs, the frequency of immunotherapy can be significantly reduced. To sum up, through prolonged skin exposure to antigen, this implantable designed MN may offer a new therapeutic strategy for FA treatment with significant improvements in efficacy and convenience. Schematic illustration of silk-PVA composite microneedles, consisting of OVA (antigen)-loaded silk microneedles and a dissolvable, flexible PVA pedestal. Once inserted into the skin, the PVA pedestal can dissolve in the interstitial fluid of the excised skin within 5 min. Subsequently, the OVA-loaded silk microneedle tips were implanted in the dermal layer as a sustained antigen depot and induced long-lasting immune response. This MNs-based immunotherapy can significantly modulate the Th1/Th2 imbalance of sensitized mice.

Treating allergies via skin - Recent advances in cutaneous allergen immunotherapy

Subcutaneous allergen immunotherapy has been practiced clinically for decades to treat airborne allergies. Recently, the cutaneous route, which exploits the immunocompetence of the skin has received attention, which is evident from attempts to use it to treat peanut allergy. Delivery of allergens into the skin is inherently impeded by the barrier imposed by stratum corneum, the top layer of the skin. While the stratum corneum barrier must be overcome for efficient allergen delivery, excessive disruption of this layer can predispose to development of allergic inflammation. Thus, the most desirable allergen delivery approach must provide a balance between the level of skin disruption and the amount of allergen delivered. Such an approach should aim to achieve high allergen delivery efficiency across various skin types independent of age and ethnicity, and optimize variables such as safety profile, allergen dosage, treatment frequency, application time and patient compliance. The ability to precisely quantify the amount of allergen being delivered into the skin is crucial since it can allow for allergen dose optimization and can promote consistency and reproducibility in treatment response. In this work we review prominent cutaneous delivery approaches, and offer a perspective on further improvisation in cutaneous allergen-specific immunotherapy.

Development of allergic rhinitis immunotherapy using antigen-loaded small extracellular vesicles

Allergic rhinitis is caused by a breakdown of the Th1/Th2 balance, in which the allergen-induced Th2 immune response predominates over the Th1 immune response, culminating in IgE-mediated anaphylaxis. In this study, we used small extracellular vesicles (sEVs), cell-derived membrane vesicles with a particle size of 100 nm, as simultaneous delivery carriers for allergens (ovalbumin, OVA) and CpG DNA, an adjuvant that can induce a Th1 immune response, for the treatment of allergic rhinitis. sEVs loaded with CpG DNA and OVA(CpG-OVA-sEVs) were successfully prepared. CpG-OVA-sEVs possessed an average particle size of 90 nm and average zeta potential of -30 mV. CpG DNA modification did not influence the uptake of sEVs by dendritic cells and CpG-OVA-sEV can activate dendritic cells. The CpG-OVA-sEVs were delivered to the nasopharynx-associated lymphoid tissue (NALT) of mice and were primarily taken up by the CD11c positive cells after intranasal administration. Intranasally administering CpG-OVA-sEVs significantly enhanced OVA-specific IgG antibody titers in mice models of allergic rhinitis, suggesting a transformed Th1/2 balance. Moreover, The CpG-OVA-sEV administration alleviated allergic symptoms compared to the control group. Further, the amount of IgE secreted in mouse serum decreased. Thus, CpG-OVA-sEVs could be a useful therapeutic method for treating allergic rhinitis.

Allergy-induced systemic inflammation impairs tendon quality

Background

Treatment of degenerating tendons still presents a major challenge, since the aetiology of tendinopathies remains poorly understood. Besides mechanical overuse, further known predisposing factors include rheumatoid arthritis, diabetes, obesity or smoking all of which combine with a systemic inflammation.

Methods

To determine whether the systemic inflammation accompanying these conditions contributes to the onset of tendinopathy, we studied the effect of a systemic inflammation induced by an allergic episode on tendon properties. To this end, we induced an allergic response in mice by exposing them to a timothy grass pollen allergen and subsequently analysed both their flexor and Achilles tendons. Additionally, we analysed data from a health survey comprising data from more than 10.000 persons for an association between the occurrence of an allergy and tendinopathy.

Findings

Biomechanical testing and histological analysis revealed that tendons from allergic mice not only showed a significant reduction of both elastic modulus and tensile stress, but also alterations of the tendon matrix. Moreover, treatment of 3D tendon-like constructs with sera from allergic mice resulted in a matrix-remodelling expression profile and the expression of macrophage-associated markers and matrix metalloproteinase 2 (MMP2) was increased in allergic Achilles tendons. Data from the human health study revealed that persons suffering from an allergy have an increased propensity to develop a tendinopathy.

Interpretation

Our study demonstrates that the presence of a systemic inflammation accompanying an allergic condition negatively impacts on tendon structure and function.

Funding

This study was financially supported by the Fund for the Advancement of Scientific Research at Paracelsus Medical University (PMU-FFF E-15/22/115-LEK), by the Land Salzburg, the Salzburger Landeskliniken (SALK, the Health Care Provider of the University Hospitals Landeskrankenhaus and Christian Doppler Klinik), the Paracelsus Medical University, Salzburg and by unrestricted grants from Bayer, AstraZeneca, Sanofi-Aventis, Boehringer-Ingelheim.

Brief exposure of skin to near-infrared laser augments early vaccine responses

Rapid establishment of herd immunity with vaccination is effective to combat emerging infectious diseases. Although the incorporation of adjuvant and intradermal (ID) injection could augment early responses to the vaccine, the current chemical or biological adjuvants are inappropriate for this purpose with their side effects and high reactogenicity in the skin. Recently, a near-infrared (NIR) laser has been shown to augment the immune response to ID vaccination and could be alternatively used for mass vaccination programs. Here, we determined the effect of NIR laser as well as licensed chemical adjuvants on the immunogenicity 1, 2, and 4 weeks after ID influenza vaccination in mice. The NIR laser adjuvant augmented early antibody responses, while the widely used alum adjuvant induced significantly delayed responses. In addition, the oil-in-water and alum adjuvants, but not the NIR laser, elicited escalated T_H2 responses with allergenic immunoglobulin E (IgE) responses. The effect of the NIR laser was significantly suppressed in the basic leucine zipper transcription factor ATF-like 3 (Batf3) knockout mice, suggesting a critical role of the cluster of differentiation 103⁺ (CD103)⁺ dendritic cells. The current preliminary study suggests that NIR laser adjuvant is an alternative strategy to chemical and biological agents to timely combat emerging infectious diseases. Moreover, its immunomodulatory property could be used to enhance the efficacy of immunotherapy for allergy and cancer.

Innovative Systems to Deliver Allergen Powder for Epicutaneous Immunotherapy

Allergy is a disorder owing to hyperimmune responses to a particular kind of substance like food and the disease remains a serious healthcare burden worldwide. This unpleasant and sometimes fatal allergic disease has been tackled vigorously by allergen-specific immunotherapy over a century, but the progress made so far is far from satisfactory for some allergies. Herein, we introduce innovative, allergen powder-based epicutaneous immunotherapies (EPIT), which could potentially serve to generate a new stream of technological possibilities that embrace the features of super safety and efficacious immunotherapy by manipulating the plasticity of the skin immune system via sufficient delivery of not only allergens but also tolerogenic adjuvants. We attempt to lay a framework to help understand immune physiology of the skin, epicutaneous delivery of powdered allergy, and potentials for tolerogenic adjuvants. Preclinical and clinical data are reviewed showing that deposition of allergen powder into an array of micropores in the epidermis can confer significant advantages over intradermal or subcutaneous injection of aqueous allergens or other epicutaneous delivery systems to induce immunological responses toward tolerance at little risk of anaphylaxis. Finally, the safety, cost-effectiveness, and acceptability of these novel EPITs are discussed, which offers the perspective of future immunotherapies with all desirable features.

CpG Adjuvant in Allergen-Specific Immunotherapy: Finding the Sweet Spot for the Induction of Immune Tolerance

Prevalence and incidence of IgE-mediated allergic diseases have increased over the past years in developed and developing countries. Allergen-specific immunotherapy (AIT) is currently the only curative treatment available for allergic diseases that has long-term efficacy. Although AIT has been proven successful as an immunomodulatory therapy since its beginnings, it still faces several unmet needs and challenges today. For instance, some patients can experience severe side effects, others are non-responders, and prolonged treatment schedules can lead to lack of patient adherence and therapy discontinuation. A common strategy to improve AIT relies on the use of adjuvants and immune modulators to boost its effects and improve its safety. Among the adjuvants tested for their clinical efficacy, CpG oligodeoxynucleotide (CpG-ODN) was investigated with limited success and without reaching phase III trials for clinical allergy treatment. However, recently discovered immune tolerance-promoting properties of CpG-ODN place this adjuvant again in a prominent position as an immune modulator for the treatment of allergic diseases. Indeed, it has been shown that the CpG-ODN dose and concentration are crucial in promoting immune regulation through the recruitment of pDCs. While low doses induce an inflammatory response, high doses of CpG-ODN trigger a tolerogenic response that can reverse a pre-established allergic milieu. Consistently, CpG-ODN has also been found to stimulate IL-10 producing B cells, so-called B regulatory cells (Bregs). Accordingly, CpG-ODN has shown its capacity to prevent and revert allergic reactions in several animal models showing its potential as both preventive and active treatment for IgE-mediated allergy. In this review, we describe how CpG-ODN-based therapies for allergic diseases, despite having shown limited success in the past, can still be exploited further as an adjuvant or immune modulator in the context of AIT and deserves additional attention. Here, we discuss the past and current knowledge, which highlights CpG-ODN as a potential adjuvant to be reevaluated for the enhancement of AIT when used in appropriate conditions and formulations.

Laser-facilitated epicutaneous immunotherapy with hypoallergenic beta-glucan neoglycoconjugates suppresses lung inflammation and avoids local side effects in a mouse model of allergic asthma

Background

Allergen‐specific immunotherapy via the skin targets a tissue rich in antigen‐presenting cells, but can be associated with local and systemic side effects. Allergen‐polysaccharide neoglycogonjugates increase immunization efficacy by targeting and activating dendritic cells via C‐type lectin receptors and reduce side effects.

Objective

We investigated the immunogenicity, allergenicity, and therapeutic efficacy of laminarin‐ovalbumin neoglycoconjugates (LamOVA).

Methods

The biological activity of LamOVA was characterized in vitro using bone marrow‐derived dendritic cells. Immunogenicity and therapeutic efficacy were analyzed in BALB/c mice. Epicutaneous immunotherapy (EPIT) was performed using fractional infrared laser ablation to generate micropores in the skin, and the effects of LamOVA on blocking IgG, IgE, cellular composition of BAL, lung, and spleen, lung function, and T‐cell polarization were assessed.

Results

Conjugation of laminarin to ovalbumin reduced its IgE binding capacity fivefold and increased its immunogenicity threefold in terms of IgG generation. EPIT with LamOVA induced significantly higher IgG levels than OVA, matching the levels induced by s.c. injection of OVA/alum (SCIT). EPIT was equally effective as SCIT in terms of blocking IgG induction and suppression of lung inflammation and airway hyperresponsiveness, but SCIT was associated with higher levels of therapy‐induced IgE and TH2 cytokines. EPIT with LamOVA induced significantly lower local skin reactions during therapy compared to unconjugated OVA.

Conclusion

Conjugation of ovalbumin to laminarin increased its immunogenicity while at the same time reducing local side effects. LamOVA EPIT via laser‐generated micropores is safe and equally effective compared to SCIT with alum, without the need for adjuvant.

Laser-assisted skin delivery of immunocontraceptive rabies nanoparticulate vaccine in poloxamer gel

A painless skin delivery of vaccine for disease prevention is of great advantage in improving compliance in patients. To test this idea as a proof of concept, we utilized a pDNA vaccine construct, pDNAg333-2GnRH that has a dual function of controlling rabies and inducing immunocontraception in animals. The pDNA was administered to mice in a nanoparticulate form delivered through the skin using the P.L.E.A.S.E.® (Precise Laser Epidermal System) microporation laser device. Laser application was well tolerated, and mild skin reaction was healed completely in 8 days. We demonstrated that adjuvanted nanoparticulate pDNA vaccine significantly upregulated the expression of co-stimulatory molecules in dendritic cells. After topical administration of the adjuvanted nano-vaccine in mice, the high avidity serum for GnRH antibodies were induced and maintained up to 9 weeks. The induced immune response was of a mixed Th1/Th2 profile as measured by IgG subclasses (IgG2a and IgG1) and cytokine levels (IFN-γ and IL-4). Using flow cytometry, we revealed an increase of CD8+ T-cells and CD45R B cells upon the administration of the adjuvanted vaccine. Our previous study used the same pDNA nanoparticulate vaccine through an IM route, and a comparable immune response was induced using P.L.E.A.S.E. However, the vaccine dose in the current study was four-fold less than what was applied through the IM route.We concluded that laser-assisted skin vaccination has a potential of becoming a safe and reliable vaccination tool for rabies vaccination in animals or even in humans for pre- or post-exposure prophylaxis.

New and old adjuvants in allergen-specific immunotherapy: With a focus on nanoparticles

Allergic diseases have remarkably increased in recent years. Nowadays, efforts for curing and management of these disorders are an important concern worldwide. Allergen-specific immunotherapy (ASIT) has recently gained more attention as a means for the management of allergic diseases. Adjuvants or helper agents are materials applied for better stimulating and shifting of protective responses, and these belong to an extremely diverse collection of complexes. The main function of adjuvants includes acting as depot foundations, transferring vehicles, and immunostimulators. Immunostimulatory adjuvants have gained increasing attention for ASIT. In this regard, the present study provides a review of old and new adjuvants used in allergen immunotherapy.

Laser-facilitated epicutaneous immunotherapy with depigmented house dust mite extract alleviates allergic responses in a mouse model of allergic lung inflammation

BACKGROUND

Skin-based immunotherapy of type 1 allergies has recently been re-investigated as an alternative for subcutaneous injections. In the current study, we employed a mouse model of house dust mite (HDM)-induced lung inflammation to explore the potential of laser-facilitated epicutaneous allergen-specific treatment.

METHODS

Mice were sensitized against native Dermatophagoides pteronyssinus extract and repeatedly treated by application of depigmented D pteronyssinus extract via laser-generated skin micropores or by subcutaneous injection with or without alum. Following aerosol challenges, lung function was determined by whole-body plethysmography and bronchoalveolar lavage fluid was analyzed for cellular composition and cytokine levels. HDM-specific IgG subclass antibodies were determined by ELISA. Serum as well as cell-bound IgE was measured by ELISA, rat basophil leukemia cell assay, and ex vivo using a basophil activation test, respectively. Cultured lymphocytes were analyzed for cytokine secretion profiles and cellular polarization by flow cytometry.

RESULTS

Immunization of mice by subcutaneous injection or epicutaneous laser microporation induced comparable IgG antibody levels, but the latter preferentially induced regulatory T cells and in general downregulated T cell cytokine production. This effect was found to be a result of the laser treatment itself, independent from extract application. Epicutaneous treatment of sensitized animals led to induction of blocking IgG, and improvement of lung function, superior compared to the effects of subcutaneous therapy. During the whole therapy schedule, no local or systemic side effects occurred.

CONCLUSION

Allergen-specific immunotherapy with depigmented HDM extract via laser-generated skin micropores offers a safe and effective treatment option for HDM-induced allergy and lung inflammation.

Laser adjuvant for vaccination

The use of an immunologic adjuvant to augment the immune response is essential for modern vaccines which are relatively ineffective on their own. In the past decade, researchers have been consistently reporting that skin treatment with a physical parameter, namely laser light, augments the immune response to vaccine and functions as an immunologic adjuvant. This "laser adjuvant" has numerous advantages over the conventional chemical or biological agents; it is free from cold chain storage, hypodermic needles, biohazardous sharp waste, irreversible formulation with vaccine antigen, undesirable biodistribution in vital organs, or unknown long-term toxicity. Since vaccine formulations are given to healthy populations, these characteristics render the "laser adjuvant" significant advantages for clinical use and open a new developmental path for a safe and effective vaccine. In addition, laser technology has been used in the clinic for more than three decades and is therefore technically matured and has been proved to be safe. Currently, four classes of laser adjuvant have been reported; ultrashort pulsed, non-pulsed, non-ablative fractional, and ablative fractional lasers. Since each class of the laser adjuvant shows a distinct mechanism of action, a proper choice is necessary to craft an effective vaccine formulation toward a desired clinical benefit for a clinical vaccine to maximize protection. In addition, data also suggest that further improvement in the efficacy is possible when a laser adjuvant is combined with chemical or biological adjuvant(s). To realize these goals, further efforts to uncover the molecular mechanisms of action of the laser adjuvants is warranted. This review provides a summary and comments of the recent updates in the laser adjuvant technology.

Delivery of allergen powder for safe and effective epicutaneous immunotherapy

BACKGROUND

More effective and safer immunotherapies to manage peanut allergy are in great demand despite extensive investigation of sublingual/oral immunotherapy and epicutaneous immunotherapy (EPIT) currently in the clinics.

OBJECTIVE

We sought to develop a powder-laden, dissolvable microneedle array (PLD-MNA) for epidermal delivery of powdered allergens and to evaluate the efficacy of this novel EPIT in peanut-sensitized mice.

METHODS

PLD-MNA was packaged with a mixture of powdered peanut allergen (PNA), 1,25-dihydroxyvitamin D₃ (VD3), and CpG. Its epidermal delivery and therapeutic efficacy were evaluated alongside PNA-specific forkhead box P3-positive regulatory T cells and IL-10⁺ and TGF-β1⁺ skin-resident macrophages.

RESULTS

PLD-MNA was successfully laden with PNA/VD3/CpG powder and capable of epidermal delivery of most of its content 1 hour after application onto intact mouse skin concomitant with no significant leakage into the circulation or skin irritation. PLD-MNA-mediated EPIT substantially reduced clinical allergy scores to 1 from 3.5 in sham control mice (P < .001) after 6 treatments accompanied by lower levels of PNA-specific IgE and intestinal mucosal mast cells and eosinophils over sham treatments. Moreover, in comparison with allergens administered intradermally, powdered allergens delivered by means of PLD-MNA preferentially attracted immunoregulatory macrophages and stimulated the cells to produce IL-10, TGF-β, or both at the immunization site, which might account for increased numbers of regulatory T-like cells in lymph tissues in association with systemic tolerance. PNA/VD3/CpG-laden PLD-MNA was safe and required only 6 treatments and one fifth of the PNA adjuvant dose, with improved outcomes when compared with 12 conventional intradermal immunotherapies.

CONCLUSIONS

PLD-MNA holds great promise as a novel, safe, effective, and self-applicable modality to manage IgE-mediated allergies.

Transcutaneous delivery of DNA/mRNA for cancer therapeutic vaccination

Therapeutic vaccination is a promising strategy for the immunotherapy of cancers. It eradicates cancer cells by evoking and strengthening the patient's own immune system. Because of the easy access and sophisticated immune networks, the skin becomes an ideal target organ for vaccination. Genetic vaccines have been widely investigated, with the advantages of the delivery of multiple antigens and a lower cost for production compared to protein/peptide vaccines. This review summarizes the advances made with respect to the transcutaneous delivery of DNA/mRNA for cancer therapeutic vaccination and also gives a brief description of the immunological milieu of the skin and the importance of dendritic cell-targeting in vaccine delivery, as well as the technologies that aim to facilitate antigen delivery and modulate antigen-presenting cells, thus improving cellular responses. The applications of genetic vaccines encoding tumor antigens delivered through the skin route, both in preclinical and clinical trials, are outlined.

Transdermal delivery of human growth hormone via laser-generated micropores

The epidermal skin barrier plays an important role in protecting underlying structures. It allows the passage of low molecular weight lipophilic molecules, but restricts the passage of hydrophilic molecules and macromolecules. The objective of this study was to investigate the feasibility of transdermal delivery of human growth hormone (hGH) through laser-microporated dermatomed porcine ear skin. The permeation of hGH was evaluated at different laser fluences and micropore densities. In vitro permeation studies were performed on vertical Franz diffusion cells using dermatomed porcine ear skin treated with ablative laser (2940 nm; P.L.E.A.S.E®, Pantec Biosolutions AG). The effect of different fluences (34.1, 45.4, and 68.1 J/cm²) at 10% pore density as well as different densities of micropores (5, 10, and 15%) at fluence of 34.1 J/cm², on the permeation of hGH was evaluated. After 48 h, 77.12 ± 10.77 μg/cm² hGH was delivered into the receptor with the application of fluence of 45.4 J/cm², which was significantly higher than that observed from 34.1 J/cm² group (53.13 ± 1.75 μg/cm², p < 0.05). Application of fluence of 68.1 J/cm² showed permeation of 90.94 ± 3.93 μg/cm² that was significantly higher than that from 34.1 J/cm² group (p < 0.05), but not as compared to the 45.4 J/cm² group (p > 0.05). With the increase in density of micropores from 5 to 15%, permeation of hGH increased significantly from 7.1 ± 2.63 μg/cm² to 95.89 ± 13.43 μg/cm² after 48 h (p < 0.05). Thus, overall, the variations in the fluence as well as micropore density of the laser were observed to influence hGH permeation, through laser-microporated dermatomed porcine skin.

Synergistic effects of dendritic cell targeting and laser-microporation on enhancing epicutaneous skin vaccination efficacy

Due to its unique immunological properties, the skin is an attractive target tissue for allergen-specific immunotherapy. In our current work, we combined a dendritic cell targeting approach with epicutaneous immunization using an ablative fractional laser to generate defined micropores in the upper layers of the skin. By coupling the major birch pollen allergen Bet v 1 to mannan from S. cerevisiae via mild periodate oxidation we generated hypoallergenic Bet-mannan neoglycoconjugates, which efficiently targeted CD14⁺ dendritic cells and Langerhans cells in human skin explants. Mannan conjugation resulted in sustained release from the skin and retention in secondary lymphoid organs, whereas unconjugated antigen showed fast renal clearance. In a mouse model, Bet-mannan neoglycoconjugates applied via laser-microporated skin synergistically elicited potent humoral and cellular immune responses, superior to intradermal injection. The induced antibody responses displayed IgE-blocking capacity, highlighting the therapeutic potential of the approach. Moreover, application via micropores, but not by intradermal injection, resulted in a mixed TH1/TH17-biased immune response. Our data clearly show that applying mannan-neoglycoconjugates to an organ rich in dendritic cells using laser-microporation is superior to intradermal injection. Due to their low IgE binding capacity and biodegradability, mannan neoglycoconjugates therefore represent an attractive formulation for allergen-specific epicutaneous immunotherapy.

Cutaneous vaccination with coated microneedles prevents development of airway allergy

Allergy cases are increasing worldwide. Currently allergies are treated after their appearance in patients. However, now there is effort to make a preventive vaccine against allergies. The rationale is to target patient populations that are already sensitized to allergens but have yet to develop severe forms of the allergic disease, or who are susceptible to allergy development but have not yet developed them. Subcutaneous injections and the sublingual route have been used as the primary mode of preventive vaccine delivery. However, injections are painful, especially considering that they have to be given repeatedly to infants or young children. The sublingual route is hard to use since infants can't be trained to hold the vaccine under their tongue. In the present study, we demonstrate a microneedle (MN)-based cutaneous preventive allergy treatment against ovalbumin (Ova)-induced airway allergy in mice. Insertion of MNs coated with Ova as a model allergen and CpG oligonucleotide as an adjuvant (MNs-CIT) into the skin significantly induced Ova specific systemic immune response. This response was similar to that induced by hypodermic-needle-based delivery of Ova using the clinically-approved subcutaneous immunotherapy (SCIT) route. MNs-CIT regulated Th2 cytokines (IL-4, IL-5 & IL-13) and anti-inflammatory cytokines (IL-10) in the bronchoalveolar fluid, and IL-2 and IFN-γ cytokines in restimulated splenocyte cultures. Absence of mucus deposition inside the bronchiole wall and low collagen around the lung bronchioles after Ova-allergen challenge further confirmed the protective role of MNs-CIT. Overall, MNs-CIT represents a novel minimally invasive cutaneous immunotherapy to prevent the progression of Ova induced airway allergy in mice.

Skin vaccination via fractional infrared laser ablation - Optimization of laser-parameters and adjuvantation

BACKGROUND

Methods to deliver an antigen into the skin in a painless, defined, and reproducible manner are essential for transcutaneous immunization (TCI). Here, we employed an ablative fractional infrared laser (P.L.E.A.S.E. Professional) to introduce clinically relevant vaccines into the skin. To elicit the highest possible antibody titers with this system, we optimized different laser parameters, such as fluence and pore number per area, and tested various adjuvants.

METHODS

BALB/c mice were immunized with Hepatitis B surface antigen (HBsAg) by laser-microporation. Adjuvants used were alum, CRM₁₉₇, monophosphoryl lipid A, heat-labile enterotoxin subunit B of E. coli (LT-B), and CpG ODN1826. The influence of different fluences (2.1 to 16.8J/cm²) and pore densities (5-15%) was investigated. Furthermore, immunogenicity of HBsAg and the commercially available conjugate vaccines ActHIB® and Menveo® applied via TCI was compared to standard i.m. injection. Antigen-specific antibody titers were assessed by luminometric ELISA.

RESULTS

Antibody titers against HBsAg were dependent on pore depth and peaked at a fluence of 8.4J/cm². Immunogenicity was independent of pore density. Adjuvantation with alum significantly reduced antibody titers after TCI, whereas other adjuvants only induced marginal changes in total IgG titers. LT-B and CpG shifted the polarization of the immune response as indicated by decreased IgG1/IgG2a ratios. HBsAg/LT-B applied via TCI induced similar antibody titers compared to i.m. injection of HBsAg/alum. In contrast to i.m. injection, we observed a dose response from 5 to 20μg after TCI. Both, ActHIB® and Menveo® induced high antibody titers after TCI, which were comparable to i.m. injection.

CONCLUSIONS

Alum, the most commonly used adjuvant, is contraindicated for transcutaneous vaccination via laser-generated micropores. TCI with optimized laser parameters induces high antibody titers, which cannot be significantly increased by the tested adjuvants. Commercially available vaccines formulated without alum have the potential for successful TCI via laser-generated micropores, without the need for reformulation.

The Use of Adjuvants for Enhancing Allergen Immunotherapy Efficacy

One key approach to increase the efficacy and the safety of immunotherapy is the use of adjuvants. However, many of the adjuvants currently in use can cause adverse events, raising concerns regarding their clinical use, and are geared toward productive immune responses but not necessarily tolerogenic responses. Thus, novel adjuvants for immunotherapy are needed and are being developed. Essential is their potential to boost appropriate tolerogenic adaptive immune responses to allergens while limiting side effects. This review provides an overview of adjuvants currently in clinical use or under development and discusses their therapeutic effect in enhancing allergen-induced tolerance.

Laser-facilitated epicutaneous immunotherapy to IgE-mediated allergy

Allergen specific immunotherapy has been shown to be the only effective treatment for long-lasting clinical benefit to IgE-mediated allergic diseases, but a fewer than 5% of patients choose the treatment because of inconvenience and a high risk of anaphylaxis. Recently, epicutaneous allergen-specific immunotherapy (EPIT) has proven effective, yet with limitations owing to strong skin reactions. We demonstrate here safer and faster EPIT, named μEPIT, by delivering powdered allergen and adjuvants into many micropores in the epidermis. We fabricated a microarray patch fractionally coated with a powder mixture of ovalbumin (OVA) model allergen, CpG, and 1,25-dihydroxyvitamin D3 (VD3). Topical application of the patch onto laser-microperforated skin resulted in a high level of epidermal delivery while greatly minimizing allergen leakage into circulation system as compared to current subcutaneous immunotherapy (SCIT). Moreover, only three times of μEPIT over two weeks could sufficiently inhibit allergen-specific IgE responses in mice suffering OVA-induced airway hyperresponsivness (AHR), which was unattainable by eight times of SCIT over three weeks. Mechanistically, μEPIT preferably enhanced IgG2a production suggesting TH1-biased immune responses and induced a high level of T-regulatory (Treg) cells against repeated allergen sensitization. The immune tolerance was confirmed by marked reduction in airway wall thickness as well as eosinophil and neutrophil infiltration into the respiratory airway. The μEPIT represents a novel and painless technology to treat IgE-mediated allergic diseases with little local skin reaction and a minimal risk of anaphylaxis.

Allergen immunotherapy for birch pollen-allergic patients: recent advances

As of today, allergen immunotherapy is performed with aqueous natural allergen extracts. Recombinant allergen vaccines are not yet commercially available, although they could provide patients with well-defined and highly consistent drug substances. As Bet v 1 is the major allergen involved in birch pollen allergy, with more than 95% of patients sensitized to this allergen, pharmaceutical-grade recombinant Bet v 1-based vaccines were produced and clinically tested. Herein, we compare the clinical results and modes of action of treatments based on either a birch pollen extract or recombinant Bet v 1 expressed as hypoallergenic or natural-like molecules. We also discuss the future of allergen immunotherapy with improved drugs intended for birch pollen-allergic patients suffering from rhinoconjunctivitis.

Nucleic acid delivery into skin for the treatment of skin disease: Proofs-of-concept, potential impact, and remaining challenges

Nucleic acids (NAs) hold significant potential for the treatment of several diseases. Topical delivery of NAs for the treatment of skin diseases is especially advantageous since it bypasses the challenges associated with systemic administration which suffers from enzymatic degradation, systemic toxicity and lack of targeting to skin. However, the skin's protective barrier function limits the delivery of NAs into skin after topical application. Here, we highlight strategies for enhancing delivery of NAs into skin, and provide evidence that translation of topical NA therapies could have a transformative impact on the treatment of skin diseases.

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.

Micro-fractional epidermal powder delivery for improved skin vaccination

Skin vaccination has gained increasing attention in the last two decades due to its improved potency compared to intramuscular vaccination. Yet, the technical difficulty and frequent local reactions hamper its broad application in the clinic. In the current study, micro-fractional epidermal powder delivery (EPD) is developed to facilitate skin vaccination and minimize local adverse effects. EPD is based on ablative fractional laser or microneedle treatment of the skin to generate microchannel (MC) arrays in the epidermis followed by topical application of powder drug/vaccine-coated array patches to deliver drug/vaccine into the skin. The novel EPD delivered more than 80% sulforhodamine b (SRB) and model antigen ovalbumin (OVA) into murine, swine, and human skin within 1h. EPD of OVA induced anti-OVA antibody titer at a level comparable to intradermal (ID) injection and was much more efficient than tape stripping in both delivery efficiency and immune responses. Strikingly, the micro-fractional delivery significantly reduced local side effects of LPS/CpG adjuvant and BCG vaccine, leading to complete skin recovery. In contrast, ID injection induced severe local reactions that persisted for weeks. While reducing local reactogenicity, EPD of OVA/LPS/CpG and BCG vaccine generated a comparable humoral immune response to ID injection. EPD of vaccinia virus encoding OVA induced significantly higher and long-lasting interferon γ-secreting CD8+ T cells than ID injection. In conclusion, EPD represents a promising technology for needle-free, painless skin vaccination with reduced local reactogenicity and at least sustained immunogenicity.

New approaches to transcutaneous immunotherapy: targeting dendritic cells with novel allergen conjugates

Purpose of review

This review summarizes recent preclinical and human studies evaluating allergen-specific immunotherapy via the transcutaneous route, and provides a rationale for the application of modified allergens with reduced allergenicity. Furthermore, it covers approaches to generate hypoallergenic conjugates for specific dendritic cell targeting.

Recent findings

Efficacy and safety of specific immunotherapy by application of allergens to the skin have been demonstrated in both animal models as well as clinical trials. However, localized adverse events have been reported, and delivery of antigens via barrier-disrupted skin has been linked to the induction of unwanted T helper 2-biased immune responses and allergic sensitization. Coupling of carbohydrates to allergens has been shown to induce formation of nanoparticles, which can specifically target dendritic cells and potentiate immune responses, and by masking B-cell epitopes, can render the molecules hypoallergenic.

Summary

Due to its abundance of immunocompetent cells, the skin represents an attractive target tissue for novel and enhanced immunotherapeutic approaches. However, in order to avoid adverse events and therapy-induced sensitizations, transcutaneous immunotherapy requires the use of formulations with reduced allergenic potential. Combining novel hypoallergenic conjugates with painless transcutaneous immunization techniques may provide an efficient and patient-friendly alternative to the standard specific immunotherapy practices.

Allergen Peptides, Recombinant Allergens and Hypoallergens for Allergen-Specific Immunotherapy

Allergic diseases are among the most common health issues worldwide. Specific immunotherapy has remained the only disease-modifying treatment, but it is not effective in all patients and may cause side effects. Over the last 25 years, allergen molecules from most prevalent allergen sources have been isolated and produced as recombinant proteins. Not only are these molecules useful in improved allergy diagnosis, but they also have the potential to revolutionize the treatment of allergic disease by means of immunotherapy. Panels of unmodified recombinant allergens have already been shown to effectively replace natural allergen extracts in therapy. Through genetic engineering, several molecules have been designed with modified immunological properties. Hypoallergens have been produced that have reduced IgE binding capacity but retained T cell reactivity and T cell peptides which stimulate allergen-specific T cells, and these have already been investigated in clinical trials. New vaccines have been recently created with both reduced IgE and T cell reactivity but retained ability to induce protective allergen-specific IgG antibodies. The latter approach works by fusing per se non-IgE reactive peptides derived from IgE binding sites of the allergens to a virus protein, which acts as a carrier and provides the T-cell help necessary for immune stimulation and protective antibody production. In this review, we will highlight the different novel approaches for immunotherapy and will report on prior and ongoing clinical studies.

Lasers as an approach for promoting drug delivery via skin

INTRODUCTION

Using lasers can be an effective drug permeation-enhancement approach for facilitating drug delivery into or across the skin. The controlled disruption and ablation of the stratum corneum (SC), the predominant barrier for drug delivery, is achieved by the use of lasers. The possible mechanisms of laser-assisted drug permeation are the direct ablation of the skin barrier, optical breakdown by a photomechanical wave and a photothermal effect. It has been demonstrated that ablative approaches for enhancing drug transport provide some advantages, including increased bioavailability, fast treatment time, quick recovery of SC integrity and the fact that skin surface contact is not needed. In recent years, the concept of using laser techniques to treat the skin has attracted increasing attention.

AREAS COVERED

This review describes recent developments in using nonablative and ablative lasers for drug absorption enhancement. This review systematically introduces the concepts and enhancement mechanisms of lasers, highlighting the potential of this technique for greatly increasing drug absorption via the skin. Lasers with different wavelengths and types are employed to increase drug permeation. These include the ruby laser, the erbium:yttrium-gallium-garnet laser, the neodymium-doped yttrium-aluminum-garnet laser and the CO2 laser. Fractional modality is a novel concept for promoting topical/transdermal drug delivery. The laser is useful in enhancing the permeation of a wide variety of permeants, such as small-molecule drugs, macromolecules and nanoparticles.

EXPERT OPINION

This potential use of the laser affords a new treatment for topical/transdermal application with significant efficacy. Further studies using a large group of humans or patients are needed to confirm and clarify the findings in animal studies. Although the laser fluence or output energy used for enhancing drug absorption is much lower than for treatment of skin disorders and rejuvenation, the safety of using lasers is still an issue. Caution should be used in optimizing the feasible conditions of the lasers in balancing the effectiveness of permeation enhancement and skin damage.

Perspectives in vaccine adjuvants for allergen-specific immunotherapy

The design of more powerful adjuvants is a tool of crucial interest to ameliorate vaccination strategies to reduce injections and/or dose of antigen, induce local immunity and obtain better protection. Effective anti-infectious vaccines should elicit protective TH1 responses, cytotoxic CD8+ cells and antibody-forming cells. However, cytokine microenvironment is a key point also in targeted therapeutic vaccinations, such as allergen-specific immunotherapy, where the interference with an already-existing but inappropriate immunity is required. In this case, safe, appropriately conditioning and potentially orally available adjuvants together with delivery to appropriate subsets of dendritic cells would be highly appreciated to properly boost innate immune cells. In fact, aluminium hydroxide, although safe, has been classically associated with the induction of a TH2 response to co-formulated antigens. Thus, detoxified lipopolysaccaride (MPL-A), CpG oligonucleotides, imidazoquinolines and adenine derivatives acting via innate sensors may represent improvements in therapeutic vaccinations for allergy as able to interfere with pathogenic TH2 cells with eventual induction of TH1 differentiation.

Adjuvants are Key Factors for the Development of Future Vaccines: Lessons from the Finlay Adjuvant Platform

The development of effective vaccines against neglected diseases, especially those associated with poverty and social deprivation, is urgently needed. Modern vaccine technologies and a better understanding of the immune response have provided scientists with the tools for rational and safer design of subunit vaccines. Often, however, subunit vaccines do not elicit strong immune responses, highlighting the need to incorporate better adjuvants; this step therefore becomes a key factor for vaccine development. In this review we outline some key features of modern vaccinology that are linked with the development of better adjuvants. In line with the increased desire to obtain novel adjuvants for future vaccines, the Finlay Adjuvant Platform offers a novel approach for the development of new and effective adjuvants. The Finlay Adjuvants (AFs), AFPL (proteoliposome), and AFCo (cochleate), were initially designed for parenteral and mucosal applications, and constitute potent adjuvants for the induction of Th1 responses against several antigens. This review summarizes the status of the Finlay technology in producing promising adjuvants for unsolved-vaccine diseases including mucosal approaches and therapeutic vaccines. Ideas related to adjuvant classification, adjuvant selection, and their possible influence on innate recognition via multiple toll-like receptors are also discussed.

An update on the use of laser technology in skin vaccination

Vaccination via skin often induces stronger immune responses than via muscle. This, in line with potential needle-free, painless delivery, makes skin a very attractive site for immunization. Yet, despite decades of effort, effective skin delivery is still in its infant stage and safe and potent adjuvants for skin vaccination remain largely undefined. We have shown that laser technologies including both fractional and non-fractional lasers can greatly augment vaccine-induced immune response without incurring any significant local and systemic side effects. Laser illumination at specific settings can accelerate the motility of antigen-presenting cells or trigger release of 'danger' signals stimulating the immune system. Moreover, several other groups including the authors explore laser technologies for needle-free transcutaneous vaccine delivery. As these laser-mediated resurfacing technologies are convenient, safe and cost-effective, their new applications in vaccination warrant clinical studies in the very near future.

Laser microporation of the skin: prospects for painless application of protective and therapeutic vaccines

Introduction:

In contrast to muscle and subcutaneous tissue, the skin is easily accessible and provides unique immunological properties. Increasing knowledge about the complex interplay of skin-associated cell types in the development of cutaneous immune responses has fueled efforts to target the skin for vaccination as well as for immunotherapy.

Areas covered:

This review provides an overview on skin layers and their resident immunocompetent cell types. Advantages and shortcomings of standard methods and innovative technologies to circumvent the outermost skin barrier are addressed. Studies employing fractional skin ablation by infrared lasers for cutaneous delivery of drugs, as well as high molecular weight molecules such as protein antigens or antibodies, are reviewed, and laserporation is introduced as a versatile transcutaneous vaccination platform. Specific targeting of the epidermis or the dermis by different laser settings, the resulting kinetics of uptake and transport and the immune response types elicited are discussed, and the potential of this transcutaneous delivery platform for allergen-specific immunotherapy is demonstrated.

Expert opinion:

Needle-free and painless vaccination approaches have the potential to replace standard methods due to their improved safety and optimal patient compliance. The use of fractional laser devices for stepwise ablation of skin layers might be advantageous for both vaccination against microbial pathogens, as well as immunotherapeutic approaches, such as allergen-specific immunotherapy. Thorough investigation of the underlying immunological mechanisms will help to provide the knowledge for a rational design of transcutaneous protective/therapeutic vaccines.