Antigen-induced suppressor T cells from the skin point of view

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

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

Epicutaneous Immunotherapy for Aeroallergen and Food Allergy

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

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

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

Control of experimental autoimmune encephalomyelitis by CD4+ suppressor T cells: peripheral versus in situ immunoregulation

The pathogenesis of experimental autoimmune encephalomyelitis (EAE) can be efficiently kept under control by specialized subsets of CD4+ T lymphocytes able to negatively regulate the function of T cells with encephalitogenic potential. A number of observations support a role for such suppressor T cells in controlling early phases of disease development at the level of peripheral lymphoid organs but there is also evidence suggesting immunoregulation within the central nervous system (CNS) microenvironment itself. This review evaluates the sites of regulation based on available data from distinct experimental models. We then discuss these aspects with reference to suppressor CD4+ T cells induced through the epicutaneous application of pure CNS antigens that confer long term protection against EAE. Finally, we give an overview of genes recently discovered to be important in regulation of the immune system that may also prove to be key players in the modulation of EAE and MS.

Initiation of adaptive immune responses by transcutaneous immunization

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