開發針對人畜共通傳染病弓蟲症之新型高效率DNA疫苗

Abstract

弓蟲症(Toxoplasmosis)為一種由Toxoplasma gondii所引起之人畜共通傳染病。其感染幾乎所有的哺乳類動物。大部分的哺乳類動物(包括人類)均為弓蟲生活史中的中間宿主，而其終宿主則為貓科動物。人類及其他哺乳類動物主要是藉由食入含有弓蟲卵囊之貓便污染的食物或飲水而感染。因此，由公衛防治的觀點看來，避免終宿主家貓感染弓蟲是防治弓蟲感染持續擴散的關鍵。弓蟲症的主要危害對像為孕婦以及免疫系統失調的個體，其會造成流死產、畸胎、胎兒智能不足等；而免疫不健全個體則會有神經症狀甚或死亡。由於目前並無有效預防弓蟲感染的疫苗問世。因此，本計畫旨在建立一以弓蟲表面抗原SAG-1為標的之AAV-DNA抗弓蟲疫苗，並以基因工程方式將現今常用之CMV啟動子置換為肌肉專一性啟動子，以達高抗原表現性、但疫苗本身免疫性低之效果，使得基因能長時間及穩定的表現。而為了使此DNA疫苗能順利製造，我們建立了一套高效能的AAV製程，用以確保疫苗之品質及效價。抗弓蟲之AAV-DNA疫苗於製備完成後，將於實驗小鼠模式中測試其保護力及安全性，以確定此疫苗之效力。我們希望藉由此疫苗之開發，能有效降低弓蟲症對於公共衛生及農業經濟上所帶來的損失。

Toxoplasma gondii is the etiological agent of toxoplasmosis and is the most frequent and best known of the parasitic diseases. Many mammals serve as intermediate hosts, and members of the cat family (Felidae) are the definitive hosts. Infection is contracted by ingesting either oocysts or meat containing live organisms. Toxoplasma infection is often asymptomatic, but pregnant individuals may suffer from stillbirth, abortion, and fetus congenital malformation. Encephalities is also an important and severe manifestation of toxoplasmosis in immunosuppressed patients and may cause to death. As the most well known parasitic disease in the world, there is no effective vaccine to protect mammals from toxoplasmosis attack. Our project is to build up an anti-SAG-1 (Toxoplasma gondii surface antigen-1) AAV (adeno-associated virus)-DNA vaccine to prevent cats from toxoplasmosis affection, for cats are the major source of infection. This vaccine will be produced in a well-established, and severely-guaranteed procedure to make the titer 5 × 10 12/ml. For the numerous advantages including stringent safety, high titer, and long-term gene expression, AAV is used as the vehicle of our DNA vaccine. Also we replace the Cytomegalovirus (CMV) promoter by muscle-specific promoter to drive the SAG-1 gene, therefore it avoids the host immune response due to virus promoter and prolongs the lifetime of the vaccine. The safety and protective efficiency of anti-SAG-1 AAV-DNA vaccine will be tested in the experimental mice model. We sincerely hope this anti-SAG-1 AAV-DNA vaccine can effectively prevent toxoplasmosis infection and lower the huge impaction of the public health and agricultural economics.