早在十九世紀初人們就懂得接種疫苗來預防疾病，隨著免疫學的發展而逐漸了解疫苗的作用方式，並發展出多元化的疫苗，包含死菌疫苗( inactivated vaccines )、減毒疫苗( attenuate vaccines )、次單位疫苗( subunit vaccines )、以及去氧核醣核酸疫苗( DNA vaccines )等。目前使用的疫苗種類各有其限制存在，DNA疫苗為1990年代新興的方法，DNA疫苗除了能有效的引起細胞性以及體液性的免疫反應，可以形成長時間的保護作用外，更具有其他疫苗的優點而無其缺點。然而DNA疫苗要能發揮功效必須先突破細胞膜和核膜這兩道屏障，將DNA送到細胞核內後，這段DNA才能經轉錄再經轉譯產生抗原蛋白引起免疫反應。因此發展一個無細胞種類、無DNA序列、DNA構形等限制的運送DNA系統是很重要的。
根據前人研究，一段含高量色氨酸的胜肽( KETWWETWWTEW )（稱為protein transduction domain，PTD）具有穿越細胞膜的功能，且不需專一性受器，因此可作為攜帶DNA穿越細胞膜的工具；另一方面，人類拓樸異構酶第一型 ( human topoisomerase I，hTopo I )的氨基端能與DNA結合，其與DNA的結合無DNA序列、DNA構形等限制，並具有nuclear localization signals ( NLS )可將DNA送至細胞核內，為運送DNA的工具最好的選擇。因此我們開發一融合蛋白PTD-TOPN，其具有PTD穿越細胞膜不需專一性受器的功能，並具有hTopo I之氨基端可與DNA的結合無DNA序列、DNA構形等限制且可將DNA送至細胞核內的特點，此融合蛋白預期將可攜帶DNA疫苗，在不傷害細胞的狀況下突破細胞膜及核膜兩大屏障，將DNA送入細胞核內，並進一步表現出抗原蛋白而引起免疫反應，達到疾病防制的效果。目前研究成果發現融合蛋白PTD-TOPN的確可以將質體DNA轉染入不只一種細胞中，未來發展應用於DNA疫苗指日可待。

The technique of delivering a foreign nucleic acid into nuclei is an essential step for research in gene therapy, DNA vaccines and genetically modified organisms. It is usually carried out through physical approaches such as electroporation and microinjection, which brings DNA through both cell and nuclear membranes. However, these physical methods usually have low efficiency and, most importantly, cause damage to the cell or nuclei that leads to undesired side effects.
The DNA delivery method is also important in the development of DNA vaccines. A DNA vaccine was invented around 1990, which can effectively induce immune responses. However, a DNA vaccine must surmount the barriers of both cell membrane and nuclear membranes this is usually carried out through stressful means, such as a gene gun or injection.
We set forth to develop a needle-free DNA delivery system by constructing a fusion protein ( PTD-TOPN ) which consists of a membrane penetration domain that is a tryptophan-rich peptide ( KETWWETWWTEW ), as well as a DNA binding domain that is the N-terminal 200 amino acid residues of the human topoisomerase I. Since the tryptophan-rich peptide has the ability to penetrate a membrane without requiring a specific receptor, and the N-terminal 200 amino acid residues of human topoisomerase I can bind with any DNA regardless the specific nucleotide sequence, we feel that PTD-TOPN has the potential to be a universal DNA delivery vehicle.
We have also demonstrated its feasibility in delivering DNA into nuclei by simply mixing a plasmid that has a GFP gene with the PTD-TOPN and then to COS-7 cells. We found that the GFP gene was expressed in COS-7 cells.
In summary, this fusion protein can be used for any DNA fragment and cells; therefore, it can be a universal method to deliver DNA.

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