Dermal enhancement: bacterial products on intact skin induce and augment organ-specific autoimmune disease

B cell tolerance to epidermal ribonuclear-associated neo-autoantigen in vivo

Defining how self-antigens are perceived by the immune system is pivotal to understand how tolerance is maintained under homeostatic conditions. Clinically relevant, natural autoantigens targeted by autoantibodies, in e.g. systemic lupus erythematosus (SLE), commonly have an intrinsic ability to engage not only the B cell receptor (BCR), but also a co-stimulatory pathway in B cells, such as the Toll-like receptor (TLR)-7 pathway. Here we developed a novel mouse model displaying inducible expression of a fluorescent epidermal neo-autoantigen carrying an OT-II T cell epitope, B cell antigen and associated ribonucleic acids capable of stimulating TLR-7. The neo-autoantigen was expressed in skin, but did not drain in intact form into draining lymph nodes, even after ultraviolet B (UVB)-stimulated induction of apoptosis in the basal layer. Adoptively transferred autoreactive B cells were excluded follicularly and perished at the T-B border in the spleen, preventing their recirculation and encounter with antigen peripherally. This transitional check-point was bypassed by crossing the reporter to a BCR knock-in line on a C4-deficient background. Adoptively transferred OT-II T cells homed rapidly into cutaneous lymph nodes and up-regulated CD69. Surprisingly, however, tolerance was not broken, as the T cells subsequently down-regulated activation markers and contracted. Our results highlight how sequestration of intracellular and peripheral antigen, the transitional B cell tolerance check-point and T cell regulation co-operate to maintain immunological tolerance in vivo.

Transcutaneous antigen delivery system

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

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

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

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

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

Mass vaccination: solutions in the skin

The skin is populated with Langerhans cells, thought to be efficient, potent antigen-presenting cells, that are capable of inducing protective immunity by targeting antigen delivery to the skin. Delivery to the skin may be accomplished by active delivery such as intradermal injection, use of patches or a combination of a universal adjuvant patch with injections. The robust immunity induced by skin targeting can lead to dose sparing, novel vaccines and immune enhancement in populations with poorly responsive immune systems, such as the elderly. Vaccine delivery with patches (transcutaneous immunization), may allow self-administration, ambient temperature stabilization and ease of storage for stockpiling, leading to a new level of efficient vaccine distribution in times of crisis such as a bioterror event or pandemic influenza outbreak. The use of an adjuvant (immunostimulant) patch with injected vaccines has been shown in clinical studies to enhance the immune response to an injected vaccine. This can be used for dose sparing in pandemic influenza vaccines in critically short supply or immune enhancement for poor responders to flu vaccines such as the elderly. Transcutaneous immunization offers a unique safety profile, as adjuvants are sequestered in the skin and only delivered systemically by Langerhans cells. This results in an excellent safety profile and allows use of extremely potent adjuvants. The combination of the skin immune system, safe use of potent adjuvants and ease of delivery suggests that skin delivery of vaccines can address multiple unmet needs for mass vaccination scenarios.

Toll-like receptor 4-induced cytokine production circumvents protection conferred by TGF-beta in coxsackievirus-mediated autoimmune myocarditis

Coxsackie B virus (CBV) infections are a leading cause of autoimmune myocarditis associated with inflammatory heart disease and sudden death in young adults. Previously, we demonstrated that transgenic expression of the immunosuppressive cytokine, transforming growth factor-beta (TGF-beta), specifically in the pancreas protected otherwise susceptible mice from CBV-mediated autoimmune myocarditis. Herein, we demonstrate that macrophages from these transgenic mice fail to upregulate the costimulatory molecule CD40 following infection, suggesting that pancreatic TGF-beta protects by limiting antigen stimulation. We further demonstrate that co-administration of LPS from Salmonella minnesota, a Toll-like receptor (TLR)-4 ligand, with CBV infection overcomes protection whereas the TLR-2 agonist, LPS from Porphyromonas gingivalis, does not. Furthermore, LPS-mediated disease induction correlates with increased levels of pro-inflammatory cytokines. Interestingly, the action of LPS (TLR-4) did not alter antibody isotype switching, increase viral replication or modulate CD40 expression. Instead, LPS breaks protection through an alternative mechanism specific to TLR-4 signaling.

IL-17 production by thymocytes upon CD3 stimulation and costimulation with microbial factors

IL-17 is a potent proinflammatory cytokine produced by activated memory T cells. Recent studies in both human autoimmune diseases and in their animal models have indicated that IL-17 rather than IFN-gamma might be the essential T-cell effector cytokine in the T-cell mediated autoimmune process. Since the thymus has a central role in maintaining T-cell self-tolerance and disturbance of thymic self-tolerance is implied in various autoimmune diseases, we here investigated the capability of murine thymocytes to produce IL-17. Our results indicate that thymocytes are a potent source of IL-17 in response to CD3 stimulation and various microbial immune stimuli and thereby show different patterns in the expression of the proinflammatory cytokines IFN-gamma and IL-17. In addition, strong differences between thymocytes and splenocytes were detected. Altered IL-17 production by thymocytes upon contact with foreign pathogens might be a key regulator in the education of adaptive immunity.

Genes mediating environment interactions in type 1 diabetes

The relative risk of type 1 (autoimmune) diabetes mellitus for a sibling of an affected patient is fifteen times that of the general population, indicating a strong genetic contribution to the disease. Yet, the incidence of diabetes in most Western communities has doubled every fifteen years since the Second World War - a rate of increase that can only possibly be explained by a major etiological effect of environment. Here, the authors provide a selective review of risk factors identified to date. Recent reports of linkage of type 1 diabetes to genes encoding pathogen pattern recognition molecules, such as toll-like receptors, are discussed, providing a testable hypothesis regarding a mechanism by which genetic and environmental influences on disease progress are integrated.

Effect of skin barrier disruption on immune responses to topically applied cross-reacting material, CRM(197), of diphtheria toxin

The high accessibility of the skin and the presence of immunocompetent cells in the epidermis makes this surface an attractive route for needle-free administration of vaccines. However, the lining of the skin by the stratum corneum is a major obstacle to vaccine delivery. In this study we examined the effect of skin barrier disruption on the immune responses to the cross-reacting material CRM(197), a nontoxic mutant of diphtheria toxin (DTx) that is considered as a vaccine candidate. Application of CRM(197), together with cholera toxin (CT), onto the tape-stripped skin of mice elicited antibody responses that had anti-DTx neutralizing activity. Vaccine delivery onto mildly ablated skin or intact skin did not elicit any detectable anti-CRM(197) antibodies. Mice immunized with CRM(197) alone onto the tape-stripped skin mounted a vigorous antigen-specific proliferative response. In contrast, the induction of cellular immunity after CRM(197) deposition onto mildly ablated or intact skin was adjuvant dependent. Furthermore, epidermal cells were activated and underwent apoptosis that was more pronounced when the stratum corneum was removed by tape stripping. Overall, these findings highlight the potential for transcutaneous delivery of CRM(197) and establish a correlation between the degree of barrier disruption and levels of antigen-specific immune responses. Moreover, these results provide the first evidence that the development of a transcutaneous immunization strategy for diphtheria, based on simple and practical methods to disrupt the skin barrier, is feasible.

The transdermal revolution

Historically, developments in transdermal drug delivery have been incremental, focusing on overcoming problems associated with the barrier properties of the skin, reducing skin irritation rates and improving the aesthetics associated with passive patch systems. More-recent advances have concentrated on the development of non-passive systems to aid delivery of larger drug molecules, such as proteins and nucleotides, as the trend for discovering and designing biopharmaceuticals continues. Fundamentally, improvements in transdermal delivery will remain incremental until there is wider acceptance of this route of administration within the pharmaceutical industry. Only then will the transdermal revolution live up to its true potential.