Bioceramic microneedle arrays are able to deliver OVA to dendritic cells in human skin

Microneedle-based vaccination into skin has several advantages over vaccination using conventional needles for intramuscular or subcutaneous injections. Microneedle (MN) arrays allow the vaccine to be delivered in a minimally invasive manner and directly into the skin, whereby the skin's superficial immune cells are not by-passed. Additionally, a systemic distribution of the vaccine may be avoided, which implies less side effects and less amount of vaccine needed. For a successful delivery, the needles need to penetrate the stratum corneum and reach the potent network of antigen-presenting dendritic cells (DCs). In this study, we evaluated patches covered with biodegradable ceramic (calcium sulphate) MNs with a tip diameter of approximately 3 μm and with two different lengths (300 and 600 μm) for their ability to penetrate and transfer the model allergen ovalbumin (OVA) into epidermis. MNs with a length of 600 μm (MN-600) and a volume average pore size of 12 ± 1 μm were more efficient in crossing the stratum corneum and to deliver OVA into CD1a⁺ DCs residing in the epidermis of human ex vivo skin, in comparison to MNs with a length of 300 μm. Quantitative in vitro release studies showed that approximately 90% of the loaded OVA could be released from MN-600 within 1 h. These findings support the further development of ceramic MNs for transcutaneous immunization.