Using a moulding process, Sullivan and colleagues fabricated the microneedle patch from polyvinylpyrrolidone (PVP) — a water-soluble polymer widely used in medicine — that encapsulated a dried form of an inactivated influenza vaccine. When the patch is applied to skin the microneedles (650 μm in length) penetrate across the epidermis and dissolve within minutes to release at least 80% of the vaccine load. An added advantage of using this delivery method is that the depth of penetration is optimized to facilitate exposure of the vaccine to the abundant population of antigen-presenting cells that are present in the skin, which helps to maximize the chance of generating robust immune responses.
Studies in mice showed that patch delivery of the influenza vaccine elicited similar antibody responses to an equivalent dose given intramuscularly in a single injection. The two routes of delivery also conferred protection when the mice were challenged with a lethal dose of influenza 30 days after vaccination. However, 90 days after mice were given a lethal dose of influenza, patch vaccinated mice had a 1,000-fold more efficient clearance of the virus from the lungs compared with the intramuscular injected mice. Detailed analysis showed that these mice had enhanced cellular immune responses and higher numbers of antibody-secreting cells in the spleen and lungs compared with those vaccinated intramuscularly, which could therefore promote a more rapid clearance of the virus from the lungs.
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