現今開發之疫苗微針貼片僅侷限於快速釋放劑型，尚無可緩釋疫苗之微針，本論文為研發一鑲嵌式緩釋疫苗之新型微針系統，由將生物可降解之幾丁聚醣(chitosan, CS)微針與水溶性聚乙烯吡咯烷酮(polyvinylpyrrolidone, PVP)和聚乙烯醇(polyvinyl alcohol, PVA)支撐陣列組成，此微針能在穿刺皮膚後，藉由體內組織液將後端支撐陣列溶解，僅留幾丁聚醣針體在皮膚中，緩慢而持續地釋放疫苗；由體外豬皮及體內大鼠穿刺測試證實，此微針貼片具有足夠之機械強度可刺穿角質層，並讓微針鑲嵌於富含抗原呈現細胞之表皮層及真皮層中(深度650700 m)，造成之微通道能夠在六小時內癒合，避免傷口感染之風險，穿刺後所產生之些微紅腫，可在三天內完全消失。將微針包覆螢光抗原後刺入老鼠背部皮膚，發現微針能在體內緩慢降解並持續釋放抗原長達28天。大鼠免疫試驗結果證實，微針僅須包覆肌肉注射40 % 之抗原量即可誘發相當或較高之抗體產生長達8週。以小鼠進行流感疫苗之免疫試驗，肌肉注射流感疫苗時，若添加幾丁聚醣溶液作為佐劑可快速增強免疫反應，在第2週即可產生高量抗體，而以微針施打流感疫苗，藉由微針在體內被緩慢降解可持續釋放出疫苗，達到類似多次補強注射(boost)效果，在接種4週時，抗體量明顯高於肌肉注射純病毒組及病毒加幾丁聚醣佐劑組，且在12週時抗體量為肌肉注射純病毒組之2.5倍。本研究所開發之貼片可溶式緩釋型幾丁聚醣微針接種不須長期黏貼貼片，即可達到經皮緩釋疫苗之目的，以較少的疫苗量，即達到類似肌肉注射的免疫反應，可有效節省疫苗量。

Currently developed microneedles for vaccine delivery always rapidly release encapsulated materials. Prolonged antigen release is highly desirable to induce a “depot” effect, which can result in a more potent and persistent immune response. This study introduces an integrated microneedle system, composed of embeddable chitosan microneedles with a dissolvable poly(vinyl pyrrolidone)/poly(vinyl alcohol) (PVP/PVA) supporting array, for complete and sustained delivery of encapsulated antigens to the skin. The strong PVP/PVA supporting array can provide mechanical strength to fully insert the microneedles into the skin. When inserted into rat and porcine skin, the skin interstitial fluid quickly dissolved the supporting array and chitosan microneedles were left within the skin for sustained drug delivery. The microneedle penetration depth was approximately 650-700 m (i.e. the total length of the microneedle), which is beneficial for targeted delivery of antigens to antigen-presenting cells in the epidermis and dermis. When the OVA-loaded microneedles were embedded in rat skin in vivo, histological examination showed that the microneedles gradually degraded and prolonged OVA releasing at the insertion sites for up to 28 days. Compared to traditional intramuscular immunization (500 g OVA), rats immunized by a lower microneedle dose of 200 g OVA showed a significantly higher OVA-specific antibody response on the second week which lasted for at least 8 weeks. Additionally, mice vaccinated with vaccine-loaded microneedles produced 2.5-fold influenza-specific antibody responses compared with those induced by the intramuscular immunization after 12 weeks. These results suggest that embeddable chitosan microneedles are a promising depot for extended delivery of encapsulated antigens, which may provide sustained immune stimulation and improve immunogenicity.

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