Immunization via hair follicles by topical application of naked DNA to normal skin

In vivo topical gene therapy for recessive dystrophic epidermolysis bullosa: a phase 1 and 2 trial

Recessive dystrophic epidermolysis bullosa (RDEB) is a lifelong genodermatosis associated with blistering, wounding, and scarring caused by mutations in COL7A1, the gene encoding the anchoring fibril component, collagen VII (C7). Here, we evaluated beremagene geperpavec (B-VEC), an engineered, non-replicating COL7A1 containing herpes simplex virus type 1 (HSV-1) vector, to treat RDEB skin. B-VEC restored C7 expression in RDEB keratinocytes, fibroblasts, RDEB mice and human RDEB xenografts. Subsequently, a randomized, placebo-controlled, phase 1 and 2 clinical trial (NCT03536143) evaluated matched wounds from nine RDEB patients receiving topical B-VEC or placebo repeatedly over 12 weeks. No grade 2 or above B-VEC-related adverse events or vector shedding or tissue-bound skin immunoreactants were noted. HSV-1 and C7 antibodies sometimes presented at baseline or increased after B-VEC treatment without an apparent impact on safety or efficacy. Primary and secondary objectives of C7 expression, anchoring fibril assembly, wound surface area reduction, duration of wound closure, and time to wound closure following B-VEC treatment were met. A patient-reported pain-severity secondary outcome was not assessed given the small proportion of wounds treated. A global assessment secondary endpoint was not pursued due to redundancy with regard to other endpoints. These studies show that B-VEC is an easily administered, safely tolerated, topical molecular corrective therapy promoting wound healing in patients with RDEB.

Vaccination into the Dermal Compartment: Techniques, Challenges, and Prospects

In 2019, an 'influenza pandemic' and 'vaccine hesitancy' were listed as two of the top 10 challenges to global health by the WHO. The skin is a unique vaccination site, due to its immune-rich milieu, which is evolutionarily primed to respond to challenge, and its ability to induce both humoral and cellular immunity. Vaccination into this dermal compartment offers a way of addressing both of the challenges presented by the WHO, as well as opening up avenues for novel vaccine formulation and dose-sparing strategies to enter the clinic. This review will provide an overview of the diverse range of vaccination techniques available to target the dermal compartment, as well as their current state, challenges, and prospects, and touch upon the formulations that have been developed to maximally benefit from these new techniques. These include needle and syringe techniques, microneedles, DNA tattooing, jet and ballistic delivery, and skin permeabilization techniques, including thermal ablation, chemical enhancers, ablation, electroporation, iontophoresis, and sonophoresis.

Gene Therapy and its Application in Dermatology

Gene therapy is an experimental technique to treat genetic diseases. It is based on the introduction of nucleic acid with the help of a vector, into a diseased cell or tissue, to correct the gene expression and thus prevent, halt, or reverse a pathological process. It is a promising treatment approach for genetic diseases, inherited diseases, vaccination, cancer, immunomodulation, as well as healing of some refractory ulcers. Both viral and nonviral vectors can be used to deliver the correct gene. An ideal vector should have the ability for sustained gene expression, acceptable coding capacity, high transduction efficiency, and devoid of mutagenicity. There are different techniques of vector delivery, but these techniques are still under research for assessment of their safety and effectiveness. The major challenges of gene therapy are immunogenicity, mutagenicity, and lack of sustainable therapeutic benefit. Despite these constraints, therapeutic success was obtained in a few genetic and inherited skin diseases. Skin being the largest, superficial, easily accessible and assessable organ of the body, may be a promising target for gene therapy research in the recent future.

Controlled Ultrasound Erosion for Transdermal Delivery and Hepatitis B Immunization

Although ultrasound is effective for transdermal delivery, it remains difficult to control the position, shape and size of localized skin transport regions. We developed an ultrasound erosion protocol to generate a single-site, circular delivery region with controlled size at the center of patched skin. We found that (i) shorter ultrasound pulses (25 cycles) with higher pulse repetition frequency (4 kHz) and higher peak negative pressure (17.0 MPa) resulted in larger (0.995 mm²) and deeper (∼300 µm) skin delivery regions with a higher success rate (94.44%); and (ii) temperature elevation of the skin increased with ultrasound exposure time, with a 30-s safety threshold. Furthermore, we found that hair follicles decreased the delivery controllability of ultrasound erosion. Therefore, we selected the skin of the hind legs of mice without dense hair follicles to deliver more than 1 μL of vaccine solution and successfully elicit immune responses against hepatitis B surface antigen.

PDL2+ CD11b+ dermal dendritic cells capture topical antigen through hair follicles to prime LAP+ Tregs

The skin immune system must discriminate between innocuous antigens and pathogens. Antigen applied topically using a Viaskin® patch elicits immune tolerance that can suppress colitis and food allergy. Here we show how topical antigen is acquired and presented by dendritic cells in the skin. Topical antigen is acquired by Langerhans cells (LC) and CD11b⁺ cDC2s but not cDC1s, and both  LCs and CD11b⁺ cDC2s reaching the lymph node can prime T cells and expand LAP⁺ Tregs. However, LCs are neither required nor sufficient for T cell priming, and have no role in tolerance induction. Conversely, IRF-4-dependent cDC2s are required for T cell priming. Acquisition of antigen in the dermis, delivery to the draining lymph node, and generation of tolerance are all absent in hairless mice. These results indicate an important function for hair follicle niche and CD11b⁺ cDC2s in antigen acquisition, and in generation of primary immune tolerance to topical antigens.

Antigen present and presented in the structures of the skin can result in immune responses that elicit tolerance, protective immunity or allergy, depending on the immunological context. Here the authors describe a key role for the hair follicle and CD11b⁺ dendritic cells in the priming of local antigenic tolerance.

Combined skin and muscle vaccination differentially impact the quality of effector T cell functions: the CUTHIVAC-001 randomized trial

Targeting of different tissues via transcutaneous (TC), intradermal (ID) and intramuscular (IM) injection has the potential to tailor the immune response to DNA vaccination. In this Phase I randomised controlled clinical trial in HIV-1 negative volunteers we investigate whether the site and mode of DNA vaccination influences the quality of the cellular immune responses. We adopted a strategy of concurrent immunization combining IM injection with either ID or TC administration. As a third arm we assessed the response to IM injection administered with electroporation (EP). The DNA plasmid encoded a MultiHIV B clade fusion protein designed to induce cellular immunity. The vaccine and regimens were well tolerated. We observed differential shaping of vaccine induced virus-specific CD4 + and CD8 + cell-mediated immune responses. DNA given by IM + EP promoted strong IFN-γ responses and potent viral inhibition. ID + IM without EP resulted in a similar pattern of response but of lower magnitude. By contrast TC + IM (without EP) shifted responses towards a more Th-17 dominated phenotype, associated with mucosal and epidermal protection. Whilst preliminary, these results offer new perspectives for differential shaping of desired cellular immunity required to fight the wide range of complex and diverse infectious diseases and cancers.

Size-dependent penetration of nanoemulsions into epidermis and hair follicles: implications for transdermal delivery and immunization

Nanoemulsions have been widely applied to dermal and transdermal drug delivery. However, whether and to what depth the integral nanoemulsions can permeate into the skin is not fully understood. In this study, an environment-responsive dye, P4, was loaded into nanoemulsions to track the transdermal translocation of the nanocarriers, while coumarin-6 was embedded to represent the cargoes. Particle size has great effects on the transdermal transportation of nanoemulsions. Integral nanoemulsions with particle size of 80 nm can diffuse into but not penetrate the viable epidermis. Instead, these nanoemulsions can efficiently fill the whole hair follicle canals and reach as deep as 588 μm underneath the dermal surfaces. The cargos are released from the nanoemulsions and diffuse into the surrounding dermal tissues. On the contrary, big nanoemulsions, with mean particle size of 500 nm, cannot penetrate the stratum corneum and can only migrate along the hair follicle canals. Nanoemulsions with median size, e.g. 200 nm, show moderate transdermal permeation effects among the three-size nanoemulsions. In addition, colocalization between nanoemulsions and immunofluorescence labeled antigen-presenting cells was observed in the epidermis and the hair follicles, implying possible capture of nanoemulsions by these cells. In conclusion, nanoemulsions are advantageous for transdermal delivery and potential in transcutaneous immunization.

Development of an Economical DNA Delivery System by "Acufection" and its Application to Skin Research

Dysregulation of immune response in skin is associated with numerous human skin disorders. Direct transfer of immune-related genes into skin tissue is a fascinating approach to investigate immune modulation of cutaneous inflammation in mouse models of human diseases. Here we present a cost-effective protocol that delivered naked DNA in mouse skin and leads to transgene expression. The method is coined "acufection", denoting acupuncture-mediated DNA transfection. To perform acufection, mouse skin was first infused with DNA in phosphate-buffered saline (PBS) and then pricked lightly with a bundle of acupuncture needles to facilitate the absorption of DNA and transfection into cells. The plasmid DNA is presumably taken up by the keratinocyte and dendritic cells (DCs) in the skin and expressed into protein. Mechanical prick with the needles per se did not cause skin damage or induce keratinocyte activation. The expression of the transfected genes was detected in the skin at both transcriptional and translational levels following acufection for 2 days and maintained up to 7 days. The primary goal for the development of this acufection method was to investigate a previously undefined isoform of IL-15. Using this method, an alternatively spliced IL-15 isoform with partially deleted exon 7 (IL-15ΔE7) was expressed in the skin and subsequently treated with a Toll-like receptor 7 (TLR7) agonist, imiquimod (IMQ), to induce inflammation. Acufection-delivered IL-15ΔE7 in skin suppressed keratinocyte proliferation, epidermal thickness and neutrophil recruitment in IMQ-induced cutaneous inflammation. With increasing interest in identifying the regulatory mechanisms of cutaneous inflammation, the protocol described here provides a cost effective and versatile alternative to the gene gun system or microseeding for DNA delivery in vivo. It may potentially allow discovery of the function of a novel gene in the skin or for investigating new treatment for cutaneous diseases.

Noninvasive Transdermal Vaccination Using Hyaluronan Nanocarriers and Laser Adjuvant

Vaccines are commonly administered by injection using needles. Although transdermal microneedles are less-invasive promising alternatives, needle-free topical vaccination without involving physical damage to the natural skin barrier is still sought after as it can further reduce needle-induced anxiety and simply administration. However, this long-standing goal has been elusive since the intact skin is impermeable to most macromolecules. Here, we show an efficient, non-invasive transdermal vaccination in mice by employing two key innovations: first, the use of hyaluronan (HA) as vaccine carriers and, second, non-ablative laser adjuvants. Conjugates of a model vaccine ovalbumin (OVA) and HA-HA-OVA conjugates-induced more effective maturation of dendritic cells in vitro, compared to OVA or HA alone, through synergistic HA receptor-mediated effects. Following topical administration in the back skin, HA-OVA conjugates penetrated into the epidermis and dermis in murine and porcine skins up to 30% of the total applied quantity, as revealed by intravital microscopy and quantitative fluorescence assay. Topical administration of HA-OVA conjugates significantly elevated both anti-OVA IgG antibody levels in serum and IgA antibody levels in bronchioalveolar lavage, with peak levels at 4 weeks, while OVA alone had a negligible effect. An OVA challenge at week 8 elicited strong immune-recall humoral responses. With pre-treatment of the skin using non-ablative fractional laser beams (1410 nm wavelength, 10 ms pulse duration, 0.2 mJ/pulse) as laser adjuvant, strong immunization was achieved with much reduced doses of HA-OVA (1 mg/kg OVA). Our results demonstrate the potential of the non-invasive patch-type transdermal vaccination platform.

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.

Cross-presentation of cutaneous melanoma antigen by migratory XCR1+CD103- and XCR1+CD103+ dendritic cells

The question of which dendritic cells (DCs) cross-present peripheral tumor antigens remains unanswered. We assessed the ability of multiple skin-derived and lymphoid resident DCs to perform this function in a novel orthotopic murine melanoma model where tumor establishment and expansion is within the skin. Two migratory populations defined as CD103^-XCR1⁺ and CD103⁺XCR1⁺ efficiently cross-presented melanoma-derived antigen, with the CD103^-XCR1⁺ DCs surprisingly dominating this process. These results are critical for understanding how antitumor CD8⁺ T cell immunity is coordinated to tumor antigens present within the skin.

Immunoprevention of chemical carcinogenesis through early recognition of oncogene mutations

Prevention of tumors induced by environmental carcinogens has not been achieved. Skin tumors produced by polyaromatic hydrocarbons, such as 7,12-dimethylbenz(a)anthracene (DMBA), often harbor an H-ras point mutation, suggesting that it is a poor target for early immunosurveillance. The application of pyrosequencing and allele-specific PCR techniques established that mutations in the genome and expression of the Mut H-ras gene could be detected as early as 1 d after DMBA application. Further, DMBA sensitization raised Mut H-ras epitope-specific CTLs capable of eliminating Mut H-ras(+) preneoplastic skin cells, demonstrating that immunosurveillance is normally induced but may be ineffective owing to insufficient effector pool size and/or immunosuppression. To test whether selective pre-expansion of CD8 T cells with specificity for the single Mut H-ras epitope was sufficient for tumor prevention, MHC class I epitope-focused lentivector-infected dendritic cell- and DNA-based vaccines were designed to bias toward CTL rather than regulatory T cell induction. Mut H-ras, but not wild-type H-ras, epitope-focused vaccination generated specific CTLs and inhibited DMBA-induced tumor initiation, growth, and progression in preventative and therapeutic settings. Transferred Mut H-ras-specific effectors induced rapid tumor regression, overcoming established tumor suppression in tumor-bearing mice. These studies support further evaluation of oncogenic mutations for their potential to act as early tumor-specific, immunogenic epitopes in expanding relevant immunosurveillance effectors to block tumor formation, rather than treating established tumors.

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.

Gene therapy for skin diseases

The skin possesses qualities that make it desirable for gene therapy, and studies have focused on gene therapy for multiple cutaneous diseases. Gene therapy uses a vector to introduce genetic material into cells to alter gene expression, negating a pathological process. This can be accomplished with a variety of viral vectors or nonviral administrations. Although results are promising, there are several potential pitfalls that must be addressed to improve the safety profile to make gene therapy widely available clinically.

The immune system of mouse vibrissae follicles: cellular composition and indications of immune privilege

Although vibrissae hair follicles (VHFs) have long been a key research model in the life sciences, their immune system (IS) is essentially unknown. Therefore, we have characterized basic parameters of the VHF-IS of C57BL/6J mice by quantitative (immuno-)histomorphometry. Murine anagen VHF harbour few CD4+ and CD8+ T cells in the distal mesenchyme and sinuses but hardly any gamma-delta T cells in their distal epithelium. MHC class II+ Langerhans cells are seeded in the VHF infundibulum, which is also surrounded by MHC class II+ and CD11b+ cells (macrophages). The number of Langerhans cells then declines sharply in the VHF bulge, and the VHF bulb lacks MHC class II+ cells. Mast cells densely populate the VHF connective tissue sheath, where they strikingly cluster around the bulge. Both the bulge and the bulb of VHF display signs of immune privilege, that is, low MHC class I and MHC class II expression and local immunoinhibitor expression (CD200, TGFβ1). This immunophenotyping study fills an important gap in the immunobiology of murine skin and identifies differences between the IS of VHF, mouse pelage and human terminal HFs. This facilitates utilizing murine VHF as a versatile organ culture model for general immunology and immune privilege research in situ.

Strengthening the skin with topical delivery of keratinocyte growth factor-1 using a novel DNA plasmid

Fragile skin, susceptible to decubitus ulcers and incidental trauma, is a problem particularly for the elderly and for those with spinal cord injury. Here, we present a simple approach to strengthen the skin by the topical delivery of keratinocyte growth factor-1 (KGF-1) DNA. In initial feasibility studies with the novel minimalized, antibiotic-free DNA expression vector, NTC8385-VA1, the reporter genes luciferase and enhanced green fluorescent protein were delivered. Transfection was documented when luciferase expression significantly increased after transfection. Microscopic imaging of enhanced green fluorescent protein-transfected skin showed green fluorescence in hair follicles, hair shafts, and dermal and superficial epithelial cells. With KGF-1 transfection, KGF-1 mRNA level and protein production were documented with quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry, respectively. Epithelial thickness of the transfected skin in the KGF group was significantly increased compared with the control vector group (26 ± 2 versus 16 ± 4 µm) at 48 hours (P = 0.045). Dermal thickness tended to be increased in the KGF group (255 ± 36 versus 162 ± 16 µm) at 120 hours (P = 0.057). Biomechanical assessment showed that the KGF-1-treated skin was significantly stronger than control vector-transfected skin. These findings indicate that topically delivered KGF-1 DNA plasmid can increase epithelial thickness and strength, demonstrating the potential of this approach to restore compromised skin.

Preparation and efficacy of Newcastle disease virus DNA vaccine encapsulated in chitosan nanoparticles

Optimal preparation conditions of Newcastle disease virus (NDV) F gene deoxyribonucleic acid (DNA) vaccine encapsulated in chitosan nanoparticles (pFNDV-CS-NPs) were determined. The pFNDV-CS-NPs were prepared according to a complex coacervation method. The pFNDV-CS-NPs were produced with good morphology, high stability, a mean diameter of 199.5 nm, encapsulation efficiency of 98.37%±0.87%, loading capacity of 36.12%±0.19%, and a zeta potential of +12.11 mV. The in vitro release assay showed that the plasmid DNA was sustainably released from the pFNDV-CS-NPs, up to 82.9%±2.9% of the total amount. Cell transfection test indicated that the vaccine expressed the F gene in cells and maintained good bioactivity. Additionally, the safety of mucosal immunity delivery system of the pFNDV-CS-NPs was also tested in vitro by cell cytotoxicity and in vivo by safety test in chickens. In vivo immunization showed that better immune responses of specific pathogen-free chickens immunized with the pFNDV-CS-NPs were induced, and prolonged release of the plasmid DNA was achieved compared to the chickens immunized with the control plasmid. This study lays the foundation for the further development of mucosal vaccines and drugs encapsulated in chitosan nanoparticles.

Topical gene electrotransfer to the epidermis of hairless guinea pig by non-invasive multielectrode array

Topical gene delivery to the epidermis has the potential to be an effective therapy for skin disorders, cutaneous cancers, vaccinations and systemic metabolic diseases. Previously, we reported on a non-invasive multielectrode array (MEA) that efficiently delivered plasmid DNA and enhanced expression to the skin of several animal models by in vivo gene electrotransfer. Here, we characterized plasmid DNA delivery with the MEA in a hairless guinea pig model, which has a similar histology and structure to human skin. Significant elevation of gene expression up to 4 logs was achieved with intradermal DNA administration followed by topical non-invasive skin gene electrotransfer. This delivery produced gene expression in the skin of hairless guinea pig up to 12 to 15 days. Gene expression was observed exclusively in the epidermis. Skin gene electrotransfer with the MEA resulted in only minimal and mild skin changes. A low level of human Factor IX was detected in the plasma of hairless guinea pig after gene electrotransfer with the MEA, although a significant increase of Factor IX was obtained in the skin of animals. These results suggest gene electrotransfer with the MEA can be a safe, efficient, non-invasive skin delivery method for skin disorders, vaccinations and potential systemic diseases where low levels of gene products are sufficient.

Particle based vaccine formulations for transcutaneous immunization

Vaccine formulations on the basis of nano- (NP) or microparticles (MP) can solve issues with stabilization, controlled release, and poor immunogenicity of antigens. Likewise transcutaneous immunization (TCI) promises superior immunogenicity as well as the advantages of needle-free application compared with conventional intramuscular injections. Thus the combination of both strategies seems to be a very valuable approach. However, until now TCI using particle based vaccine formulations has made no impact on medical practice. One of the main difficulties is that NPs and MPs cannot penetrate the skin to an extent that would allow the application of the required dose of antigen. This is due to the formidable stratum corneum (SC) barrier, the limited amount of antigen in the formulation and often an insufficient immunogenicity. A multitude of strategies are currently under investigation to overcome these issues. We highlight selected methods presenting a spectrum of solutions ranging from transfollicular delivery, to devices disrupting the SC barrier and the combination of particle based vaccines with adjuvants discussing their advantages and shortcomings. Some of these are currently at an experimental state while others are already in clinical testing. All methods have been shown to be capable of transcutaneous antigen delivery.

Preparation and efficacy of a live newcastle disease virus vaccine encapsulated in chitosan nanoparticles

BACKGROUND

Newcastle disease (ND) is a highly contagious viral disease of poultry caused by pathogenic strains of the Newcastle disease virus (NDV). Live NDV vaccines are administered by drinking water, eyedrops or coarse aerosol spray. To further enhance mucosal immune responses, chitosan nanoparticles were developed for the mucosal delivery of a live NDV vaccine.

METHODOLOGY/PRINCIPAL FINDINGS

A lentogenic live-virus vaccine (strain LaSota) against NDV encapsulated in chitosan nanoparticles were developed using an ionic crosslinking method. Chitosan nanoparticles containing the lentogenic live-virus vaccine against NDV (NDV-CS-NPs) were produced with good morphology, high stability, a mean diameter of 371.1 nm, an encapsulation rate of 77% and a zeta potential of +2.84 mV. The Western blotting analysis showed that NDV structural proteins were detected in NDV-CS-NPs. The virus release assay results of NDV-CS-NPs indicated that NDV was released from NDV-CS-NPs. Chickens immunized orally or intranasally with NDV-CS-NPs were fully protected whereas one out of five chickens immunized with the LaSota live NDV vaccine and three out of five chickens immunized with the inactivated NDV vaccine were dead after challenge with the highly virulent NDV strain F48E9.

CONCLUSIONS/SIGNIFICANCE

NDV-CS-NPs induced better protection of immunized specific pathogen free chickens compared to the live NDV vaccine strain LaSota and the inactivated NDV vaccine. This study lays a foundation for the further development of mucosal vaccines and drugs encapsulated in chitosan nanoparticles.

Niosomes as a propitious carrier for topical drug delivery

INTRODUCTION

Topical delivery is defined as drug targeting to the pathologic sites of skin with the least systemic absorption. Drug localization in this case is a crucial issue. For these purposes vesicular drug delivery systems including niosomes, proniosomes, liposomes and transferosomes have been developed.

AREAS COVERED

This review first highlights the role of niosome in dermatology focusing on localized skin delivery and then reviews the most recent literatures regarding specific applications of niosomal drug delivery systems in clinics.

EXPERT OPINION

Niosomes are becoming popular in the field of topical drug delivery due to their outstanding characteristics like enhancing the penetration of drugs, providing a sustained pattern of drug release, increasing drug stability and ability to carry both hydrophilic and lipophilic drugs.

Transcutaneous DNA immunization following waxing-based hair depilation elicits both humoral and cellular immune responses

Previously, we showed that transcutaneous (TC) DNA immunization by applying plasmid DNA onto a mouse skin area wherein the hair follicles were induced into growth stage by plucking the hair using warm waxing induced strong and functional antigen-specific antibody responses. In the present study, using plasmids that encode β-galactosidase gene or ovalbumin (OVA) gene, we showed that this mode of TC DNA immunization not only induced specific antibody responses, but also induced antigen-specific cytotoxic T lymphocyte responses. In fact, TC DNA immunization using a plasmid that encodes OVA gene prevented the growth of OVA-expressing B16-OVA tumor cells in the immunized mice. Moreover, we provided additional evidence supporting that hair follicles are essential for this mode of TC DNA immunization.

Preparation and immunological effectiveness of a swine influenza DNA vaccine encapsulated in chitosan nanoparticles

Preparation conditions of a DNA vaccine against swine influenza encapsulated in chitosan nanoparticles were determined. The nanoparticles were prepared according to a complex coacervation method using chitosan as a biodegradable matrix forming polymer. Under the preparation conditions, chitosan nanoparticles containing the DNA vaccine were produced with good morphology, high encapsulation rate and high stability. Transfection test indicated that the vaccine could be expressed as an antigen in cells, and maintained good bioactivity. In addition, better immune responses of mice immunized with the chitosan nanoparticles containing the DNA vaccine were induced and prolonged release of the plasmid DNA was achieved compared to the DNA vaccine alone. These results laid a foundation for further development of DNA vaccines in nanoparticles before ultimate industrial application.

Transcutaneous DNA immunization following waxing-based hair depilation

Transcutaneous DNA immunization is an attractive immunization approach. Previously, we reported that transcutaneous immunization by applying plasmid DNA onto a skin area wherein the hair follicles had been induced into growth stage by 'cold' waxing-based hair plucking significantly enhanced the resultant immune responses. In the present study, using a plasmid that encodes the Bacillus anthracis protective antigen (PA63) gene fragment, it was shown that the anti-PA63 antibody responses induced by applying the plasmid onto a skin area where the hair was plucked by 'warm' waxing were significantly stronger than by 'cold' waxing, very likely because the 'warm' waxing-based hair depilation significantly i) enhanced the uptake (or retention) of the plasmid in the application area and ii) enhanced the expression of the transfected gene in the follicular and interfollicular epidermis in the skin. The antibody response induced by transcutaneous DNA immunization was hair cycle dependent, because the plasmid needed to be applied within 5days after the hair plucking to induce a strong antibody response. The antibody responses were not affected by whether the expressed PA63 protein, as an antigen, was secreted or cell surface bound. Finally, this strategy of enhancing the immune responses induced by transcutaneous DNA immunization following 'warm' waxing-based hair depilation was not limited to the PA63 as an antigen, because immunization with a plasmid that encodes the HIV-1 env gp160 gene induced a strong anti-gp160 response as well. Transcutaneous DNA immunization by modifying the hair follicle cycle may hold a great promise in inducing strong and functional immune responses.

Nanoparticles for transcutaneous vaccination

The living epidermis and dermis are rich in antigen presenting cells (APCs). Their activation can elicit a strong humoral and cellular immune response as well as mucosal immunity. Therefore, the skin is a very attractive site for vaccination, and an intradermal application of antigen may be much more effective than a subcutaneous or intramuscular injection. However, the stratum corneum (SC) is a most effective barrier against the invasion of topically applied vaccines. Products which have reached the stage of clinical testing, avoid this problem by injecting the nano‐vaccine intradermally or by employing a barrier disrupting method and applying the vaccine to a relatively large skin area. Needle‐free vaccination is desirable from a number of aspects: ease of application, improved patient acceptance and less risk of infection among them. Nanocarriers can be designed in a way that they can overcome the SC. Also incorporation into nanocarriers protects instable antigen from degradation, improves uptake and processing by APCs, and facilitates endosomal escape and nuclear delivery of DNA vaccines. In addition, sustained release systems may build a depot in the tissue gradually releasing antigen which may avoid booster doses. Therefore, nanoformulations of vaccines for transcutaneous immunization are currently a very dynamic field of research. Among the huge variety of nanocarrier systems that are investigated hopes lie on ultra‐flexible liposomes, superfine rigid nanoparticles and nanocarriers, which are taken up by hair follicles. The potential and pitfalls associated with these three classes of carriers will be discussed.

Combined gene and stem cell therapy for cutaneous wound healing

In current medical practice, wound therapy remains a clinical challenge and much effort has been focused on the development of novel therapeutic approaches for wound treatment. Gene therapy, initially developed for treatment of congenital defects, represents a promising option for enhancing wound repair. In order to accelerate wound closure, genes encoding for growth factors or cytokines have shown the most potential. The majority of gene delivery systems are based on viral transfection, naked DNA application, high pressure injection, and liposomal vectors. Besides advances stemming from breakthroughs in recombinant growth factors and bioengineered skin, there has been a significant increase in the understanding of stem cell biology in the field of cutaneous wound healing. A variety of sources, such as bone marrow, umbilical cord blood, adipose tissue and skin/hair follicles, have been utilized to isolate stem cells and to modulate the healing response of acute and chronic wounds. Recent data have demonstrated the feasibility of autologous adult stem cell therapy in cutaneous repair and regeneration. Very recently, stem cell based skin engineering in conjunction with gene recombination, in which the stem cells act as both the seed cells and the vehicle for gene delivery to the wound site, represents the most attractive field for generating a regenerative strategy for wound therapy. The aim of this article is to discuss the use and the potential of these novel technologies in order to improve wound healing capacities.

The extent of the uptake of plasmid into the skin determines the immune responses induced by a DNA vaccine applied topically onto the skin

OBJECTIVES

Non-invasive immunization by application of plasmid DNA topically onto the skin is an attractive immunization approach. However, the immune responses induced are generally weak. Previously, we showed that the antibody responses induced by topical DNA vaccine are significantly enhanced when hair follicles in the application area are induced into the anagen (growth) stage by hair plucking. In the present study, we further investigated the mechanism of immune enhancement.

METHODS

Three different methods--hair plucking or treatment with retinoic acid (RA) or O-tetradecanoylphorbol-13-acetate (TPA)--were used to induce mice hair follicles into the anagen stage before they were dosed with a β-galactosidase-encoding plasmid, and the specific antibody responses induced were evaluated.

KEY FINDINGS

The hair-plucking method was more effective at enhancing the resultant antibody responses. Treatment with RA or TPA caused more damage to the skin and induced more severe local inflammation than hair plucking. However, hair plucking was most effective at enhancing the uptake or retention of the DNA in the application area.

CONCLUSIONS

The uptake of plasmid DNA in the application area correlated with the antibody responses induced by a topically applied DNA.

Progress towards a needle-free hepatitis B vaccine

Hepatitis B virus (HBV) infection is a worldwide public health problem. Vaccination is the most efficient way to prevent hepatitis B. Despite the success of the currently available vaccine, there is a clear need for the development of new generation of HBV vaccines. Needle-free immunization is an attractive approach for mass immunization campaigns, since avoiding the use of needles reduces the risk of needle-borne diseases and prevents needle-stick injuries and pain, thus augmenting patient compliance and eliminating the need for trained medical personnel. Moreover, this kind of immunization was shown to induce good systemic as well as mucosal immunological responses, which is important for the creation of both a prophylactic and therapeutic vaccine. In order to produce a better, safer, more efficient and more suitable vaccine, adjuvants have been used. In this article, several adjuvants tested over the years for their potential to help create a needle-free vaccine against HBV are reviewed.

Preferential amplification of CD8 effector-T cells after transcutaneous application of an inactivated influenza vaccine: a randomized phase I trial

BACKGROUND

Current conventional vaccination approaches do not induce potent CD8 T-cell responses for fighting mostly variable viral diseases such as influenza, avian influenza viruses or HIV. Following our recent study on vaccine penetration by targeting of vaccine to human hair follicular ducts surrounded by Langerhans cells, we tested in the first randomized Phase-Ia trial based on hair follicle penetration (namely transcutaneous route) the induction of virus-specific CD8 T cell responses.

METHODS AND FINDINGS

We chose the inactivated influenza vaccine - a conventional licensed tetanus/influenza (TETAGRIP) vaccine - to compare the safety and immunogenicity of transcutaneous (TC) versus IM immunization in two randomized controlled, multi-center Phase I trials including 24 healthy-volunteers and 12 HIV-infected patients. Vaccination was performed by application of inactivated influenza vaccine according to a standard protocol allowing the opening of the hair duct for the TC route or needle-injection for the IM route. We demonstrated that the safety of the two routes was similar. We showed the superiority of TC application, but not the IM route, to induce a significant increase in influenza-specific CD8 cytokine-producing cells in healthy-volunteers and in HIV-infected patients. However, these routes did not differ significantly for the induction of influenza-specific CD4 responses, and neutralizing antibodies were induced only by the IM route. The CD8 cell response is thus the major immune response observed after TC vaccination.

CONCLUSIONS

This Phase Ia clinical trial (Manon05) testing an anti-influenza vaccine demonstrated that vaccines designed for antibody induction by the IM route, generate vaccine-specific CD8 T cells when administered transcutaneously. These results underline the necessity of adapting vaccination strategies to control complex infectious diseases when CD8 cellular responses are crucial. Our work opens up a key area for the development of preventive and therapeutic vaccines for diseases in which CD8 cells play a crucial role.

TRIAL REGISTRATION

Clinicaltrials.gov NCT00261001.

Induction of Specific CD8 T Cells against Intracellular Bacteria by CD8 T-Cell-Oriented Immunization Approaches

For protection against intracellular bacteria such as Mycobacterium tuberculosis and Listeria monocytogenes, the cellular arm of adaptive immunity is necessary. A variety of immunization methods have been evaluated and are reported to induce specific CD8⁺ T cells against intracellular bacterial infection. Modified BCG vaccines have been examined to enhance CD8⁺ T-cell responses. Naked DNA vaccination is a promising strategy to induce CD8⁺ T cells. In addition to this strategy, live attenuated intracellular bacteria such as Shigella, Salmonella, and Listeria have been utilized as carriers of DNA vaccines in animal models. Vaccination with dendritic cells pulsed with antigenic peptides or the cells introduced antigen genes by virus vectors such as retroviruses is also a powerful strategy. Furthermore, vaccination with recombinant lentivirus has been attempted to induce specific CD8⁺ T cells. Combinations of these strategies (prime-boost immunization) have been studied for the efficient induction of intracellular bacteria-specific CD8⁺ T cells.

Understanding the murine cutaneous dendritic cell network to improve intradermal vaccination strategies

Dendritic cells (DCs) form a heterogeneous group of antigen presenting cells that play different roles in tissue immunity. Recent studies have revealed the presence of distinct DC populations in murine skin, highlighting the complexity of the cutaneous DC network. In this review, we will define the major DC subsets that populate the different layers of the skin, focusing on their origin and the mechanisms controlling their homeostasis. We will also review recent evidence underlining the functional specialization of dermal DC subsets and its relevance in the design of novel vaccine approaches.

Stem cells and tissue-engineered skin

Advances in tissue engineering of skin are needed for clinical applications (as in wound healing and gene therapy) for cutaneous and systemic diseases. In this paper we review the use of epidermal stem cells as a source of cells to improve tissue-engineered skin. We discuss the importance and limitations of epidermal stem cell isolation using biomarkers, in quest of a pure stem cell preparation, as well as the culture conditions necessary to maintain this purity as required for a qualitatively superior and long-lasting engineered skin. Finally, we review the advantages of using additional multipotent stem cell sources to functionally and cosmetically optimize the engineered tissue.

Comparison of intramuscular and footpad subcutaneous immunization with DNA vaccine encoding HSV-gD2 in mice

Herpes simplex virus type 2 is the most common infectious agent in humans that causes genital herpes disease and vaccination is a desirable method to prevent herpes infections. An effective therapeutic vaccine will need to elicit virus-specific immune responses. The route of immunization has important role in immune responses. In this study, DNA vaccine encoding glycoprotein D of herpes simplex virus type 2 (HSV-gD2) was prepared and injected via intramuscular and footpad routes to determine the optimal method of delivery for immune stimulation. The control manipulation of immune response by concerning route of administration is highly appreciated issue by researches. Although DNA vaccine containing HSV-gD2 is effective in both intramuscular and footpad injection routes, the latter could induce significantly higher cellular responses against HSV-2.

Transcutaneous anti-influenza vaccination promotes both CD4 and CD8 T cell immune responses in humans

Induction of T cell responses has become one of the major goals in therapeutic vaccination against viral diseases and cancer. The use of the skin as target organ for vaccine has been spurred by recent implication of epithelial dendritic cells in CD8 cell cross-priming and suggests that vaccination via the transcutaneous (TC) route may be relevant in the induction of cellular immune responses. We have previously shown that TC application of nanoparticles, on human skin explants, allows targeting of epidermal dendritic cells, possibly via hair follicles. In this study, we have investigated cellular immune responses against an influenza protein-based vaccine by TC vaccination, compared with i.m. vaccination in humans. In this study on 11 healthy volunteers, we found that a newly developed protocol based on cyanoacrylate skin surface stripping induced a significant increase in IFN-gamma-producing T cells specific for influenza vaccine by ELISPOT assays. Interestingly, TC vaccination induced both effector CD4 and CD8 T cell responses, whereas i.m. injection induced strong effector CD4 in the absence of CD8 T cells, as assessed by intracellular cytokine staining and tetramer analyses. This study proposes new perspectives for the development of vaccination strategies that trigger T cell immune responses in humans.

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.

Immunization by Application of DNA Vaccine onto a Skin Area Wherein the Hair Follicles Have Been Induced into Anagen-onset Stage

An attractive approach to immunization is to apply DNA vaccine topically onto the skin. However, it is important to ensure that a strong immune response is induced without disrupting the skin stratum corneum. The hair follicles have been shown to be the major portal of entry for DNA applied onto the skin, and it has been reported that the transfection of hair follicle cells occurs mainly at the onset of a new growing stage of the hair cycle. Using an anthrax protective antigen (PA) protein-encoding plasmid in mice, we demonstrated that the anti-PA immune responses were significantly stronger when the hair follicles in the application area were induced into anagen-onset stage than when in telogen stage. The anti-PA antibodies enabled the immunized mice to survive a lethal dose of anthrax lethal toxin challenge. The enhanced immune responses can be partially attributed to the enhanced antigen gene expression and plasmid DNA uptake in the skin area wherein the hair follicles were induced into anagen-onset stage. Moreover, the moderate dermal inflammation associated with the anagen induction may also have contributed to the enhancement of the resultant immune response. This represents a novel approach to enhancing the immune response induced by a topically applied DNA vaccine.

The potential of topical DNA vaccines adjuvanted by cytokines

To improve the efficacy of DNA immunization epidermal Langerhans cells are attractive targets to deliver antigen-encoding plasmid DNA. Topical vaccination with naked plasmid DNA has been shown to induce immune responses, and their potency might be improved by chemical and physical methods aimed to enhance the efficiency of plasmid DNA delivery into the skin. Cytokines have also been evaluated as adjuvants for DNA vaccines because they influence the host immune response. This review focuses on the action of several cytokines tested as molecular adjuvants for DNA vaccines and the combination of them with the DermaVir Patch vaccine. DermaVir vaccine, topically administered under a patch, consists of a plasmid DNA that is chemically formulated into a nanoparticle to support vaccine delivery into epidermal Langerhans cells and to induce antigen-specific memory T cells.

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.