Reducing allergic airway inflammation with high-density microprojection array skin patches

Abstract

Inflammation of the airways can be life threatening for those with T helper type 2 (Th2)-mediated allergies or allergic asthma. Despite the increasing prevalence of allergic diseases, there are no current vaccinations to prevent allergies. Desensitisation via allergy immunotherapy (AIT) is the only disease-modifying treatment available. This involves slowly building up a specific-tolerance to the allergic substance (allergen) through either subcutaneous injection or oral absorption. Yet allergy patients rarely undertake AIT as is it costly, time consuming and can increase the risk of life threatening anaphylaxis. These discouraging factors arise from the poorly optimised targeting of the current routes of AIT that do not target immunotherapy primarily to tolerant-inclined cells in order to maximise an allergen-specific tolerance response.Building allergen-specific tolerance is often similar either before (vaccination therapy) or after (desensitisation therapy) allergen sensitisation. Specific-tolerance is established when tolerant-inclined cells, such as skin epidermal Langerhans cells (LCs), present allergens to the immune system alongside tolerant signalling. Targeting the therapy to the skin has been notoriously challenging with current needle and syringe or topical patch methods. However, microprojection array (MPA) patches have begun to demonstrate rapid delivery of vaccine therapeutics as well as specific cell targeting into the upper layers of the skin. Immunisation with high-density (i.e. above 1,000 (1k) projections (p)/cm2) dermal-targeted MPAs (dMPA) have previously been shown to induce pro-inflammatory and specific-IgG responses at a fraction of the injectable dose. As an increase in IgG correlates with a decrease in IgE during AIT, I hypothesised that the dMPA-therapy could specifically inhibit IgE in a desensitisation model. After initial results, I further hypothesised that a MPA that delivered allergen primarily to the epidermal LCs (eMPA) would prevent Th2 inflammation in a vaccination model, similar to that seen in a healthy immunity against allergens. Therefore, different designs of dMPAs were tested in desensitisation therapy and eMPAs in preventative vaccination therapy with an ovalbumin (OVA)-based, IgE-mediated, airway hypersensitivity mouse model.First, conical-shaped dMPAs of two densities (21k or 10k p/cm2) delivered OVA at application energies of either 170 mJ or 100 mJ to the skin of OVA sensitised BALB/c mice. Desensitisation with the very high density 21k-dMPA significantly increased unwanted Th2 responses including airway eosinophilia and anti-OVA IgE. Based on these results, the dMPA was tailored to reduce the impact on the skin by halving the projection density to 10k and using an application energy of 100 mJ. Despite the increased anti-OVA IgG1 and IgG2a, the anti-OVA IgE continued to persist. Yet, both airway eosinophilia and the level airway mucus was significantly reduced at day 87 in 10k-dMPA-100 mJ treated mice. To date, the association between repeated OVA-dMPA treatments (without adjuvants) on preventing airway eosinophilia and mucus has not been reported.Second, after establishing a strong correlation between decreased dMPA density and Th2-mediation of the immune response, I aimed to test a low inflammatory eMPA in vaccination. To date, no MPA design was reported to successfully target therapeutics to the epidermis of mouse skin. To ensure a shallow (~15 µm) but consistent epidermal delivery, projection tips were widened from the pointed conical shape to a slit-like shape, increasing the tip surface area. Slit-shaped eMPAs applied at 30 mJ resulted in significantly less erythema and epidermal inflammation than dMPAs. Analyses of the inguinal skin draining lymph nodes found that eMPAs (with or without OVA) significantly increased LC migration, but not dermal dendritic cell migration. This is the first report of MPAs targeting the mouse epidermis and preferentially activating LC migration.Third, various doses of OVA delivered by low-impact eMPAs were applied to naive mice to test prevention of Th2 airway inflammation. Compared to the positive control (80-200 µg), the eMPA prevented airway eosinophilia in up to 60% of mice and anti-OVA IgE in 75% of those mice with a significantly lower dose (0.4 µg). Additionally, mice vaccinated with eMPAs had significantly less airway mucus and obstructions even when challenged with a chronic sensitisation model. Therefore, unlike other transdermal quick-delivery devices, the eMPA showed promise in preventing airway hypersensitivity by delivering just the allergen.In conclusion, by reducing the impact on the skin, both dMPAs and eMPAs applied to mouse skin reduced airway inflammation. Only desensitisation with 10k-dMPAs at 100 mJ reduced airway eosinophilia, suggesting high densities and/or application energies are too Th2-mediated to prevent eosinophilia. Similarly, only vaccination with fewer eMPA repeats applied with lower doses prevented airway inflammation, suggesting that eMPA vaccination is dependent on the level of impact on the skin and dose delivered. These findings show promise for the future use of high-density MPAs as a skin deliver device of allergen against airway hypersensitivity but highlights the importance of understanding the new variables such as application energies and overall impact the MPA design has on the skin during MPA delivery of allergen.