對基因療法(GENE THERAPY)有何看法﹖

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“另類”療病法﹐基因療法(Gene Therapy), 大家有什麼意見﹖

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轉載﹕

基因治療

2000/12/27  張效銘 大同大學 生物工程系研究所



        遺傳工程技術的發展，為人類是世世代代難以解決的醫療問題，提供更佳的解決之道。由1960-1970年間，一些產生變性的病毒有進一步的了解，開始友人嘗試以此為一個載體將外來基因送入一個特定的細胞內。隨著這個技術的發展及對疾病的逐漸認知，於是基因治療的觀念因而衍生。

        人體基因治療的定義，所謂的基因治療(gene therapy)是指利用分子生物學中DNA重組(DNA recombination)以及轉殖的技術，把重組之DNA分子傳遞至一個或多個人體染色體內，將患者有遺傳性、新陳代謝或癌症等疾病患者細胞內的治病基因，加以修補或置換，使其恢復正常功能。或者在已喪失功能的基因外，輸入額外的正常基因，以製造必要的產物，使病人得以恢復健康的現代醫療科技。

DNA的重組技術乃是基因治療的基本操作，所謂重組DNA分子意指：

在活的細胞外，把自然存在的或人工合成的DNA分子片段接合至其他的DNA分子之上，而由此形成的DNA分子組合若被送入活的細胞之內，是可以隨細胞繼續增殖的。


由上述帶轉殖基因的細胞增殖而成的分子產物。

基因治療對人體而言，其適用範圍僅限於體細胞基因治療，禁止施行於生殖細胞基因治療。人體的細胞可區分為體細胞(somatic cell)和生殖細胞(germ cell)二大類。到目前為止，已在世界各國進行的基因治療試驗，均有嚴格限制，只能施用於體細胞而禁止施用於生殖細胞。因為把一個人體細胞裡的害基因加以置換或增補，其所產生的後果無論好壞，只會影響接受治療本人而不會影響其後代，因此尚可為民間、宗教界、科學界、醫界所接受。反之，若以生殖細胞為基因治療的施用對象，將會使基因的變異傳到個體的後代，其對於人類的影響過於深遠，禍福殊難預料，也為宗教和倫理所不容，因此，世界各國對於基因治療試驗均嚴格限制於體細胞，我國亦然。故基因治療人體試驗概以體細胞治療為限。

        一個好的、有效率的基因轉殖是基因治療的第一要件。針對不同的標的細胞，基因轉殖方法及效率可能各自不同。且須根據疾病或標的細胞的不同而作適當的選擇。常用基因治療之基因轉殖方法有：

(一) 病毒載體的方法

反轉錄病毒載體(Retroviral Vector)：目前使用最多的，其為帶有鞘膜(envelop)的RNA病毒。其可經由反轉錄酵素作用形成雙股DNA，再嵌插在宿主染色體中，達到基因轉殖及持續性表現的特性。此類型病毒使用需顧慮嵌插時造成的突變(insertional mutagenesis)及造成可複製能力的野生種病毒(replication competent virus, RCV)產生等問題，因為若在packaging cell line內發生基因重組，會導致野生型RCV的產生，則會使嵌插所造成的突變機率變大。


腺病毒載體(Adenoviral Vector)：為一剔除E1及E3基因的DNA病毒，其利用同源基因重組(homologous recombination)，將基因表現部分的質體與絕大部分的病毒因體同時送入細胞，經重組後，在由其所提供的E1基因來複製重組病毒，用以感染標的細胞。


(二) 非病毒載體的方法

微脂粒法之基因轉殖(liposome-mediated gene transfer)：其利用一些磷脂類，具不帶電性或極性者，以不同比例組合形成微脂粒，再將核酸與這些微脂粒混合，將DNA包裹其中，直接通過細胞膜送入細胞內。


受體引導之基因轉殖(Receptor-mediated gene transfer)：其利用DNA特異性帶入某些細胞，將可受體之對應配位體(ligand)以化學方法接上polylysine，由於polylysine帶有極端的正電荷，故可與DNA結合。藉由配位體與受體的結合，可將DNA經由胞飲作用(endocytosis)進入細胞內。


參考資料：生物技術(九州圖書文物有限公司)、衛生署公告(88年元月)、生物技術概論(藝軒圖書出版社)。

铁蛋

不是搞笑的，利用 retroviral vector 的实验曾失败，有病者因而得到癌症而死。目前这类技术还不稳定。

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轉載﹕Nature 429, 587 (10 June 2004); doi:10.1038/429587a  


Gene therapists hopeful as trials resume with childhood disease

ERIKA CHECK


[MINNEAPOLIS] A French gene-therapy trial that cured nine children of a severe disease, but gave two of them cancer, looks set to restart after a 22-month suspension.

The trial involves children who suffer from severe combined immunodeficiency disease (SCID). These children lack innate defences against infections and without treatment they can only survive in isolated environments. One US gene-therapy trial for the disease has also restarted, and others are likely to resume this year.

The suspension of the trials had deeply shaken the gene-therapy field, because SCID was the only disease that had ever been cured by such therapy. Researchers at the annual meeting of the American Society of Gene Therapy in Minneapolis, Minnesota, last week saw the resumption of the SCID trials as a bright spot after a long dark spell for the field.

Specialists say there is still a risk that some children will develop cancer during the trials. But they say the trials should proceed, because the French technique has cured many children who suffer from the devastating illness.

"We're moving forward," says Donald Kohn, past president of the American Society of Gene Therapy and leader of one of the US trials. "No therapy is without risk, and now that we've had time to look back, we realize that this therapy even with the risk may be better than the current treatment," Kohn says.

The children in the French trial suffer from a version of the disease called X-linked SCID. For X-linked SCID patients, the alternative to gene therapy is a bone-marrow transplant. But these transplants are successful in only 70% of children, unless they have a suitable bone-marrow donor. Out of 18 children treated using gene therapy, 15 appear to have been cured of X-linked SCID.

The French trial, led by Alain Fischer of the Necker Hospital in Paris, was the first to show that infants could be cured through doses of a gene to correct their genetic deficiency. But in September 2002, Fischer announced that he had halted his trial because one of the participants had developed leukaemia. Another child came down with leukaemia a few months later. Both are alive and recovering from their cancers.

Fischer's announcement prompted the US Food and Drug Administration (FDA) to stop three gene-therapy trials in America — two in X-linked SCID, and one in another form of the disease called ADA-SCID. But an X-linked SCID study in Britain was allowed to continue, and seven children have now been treated in that study. Claudio Bordignon of the San Raffaele Telethon Institute for Gene Therapy in Milan, Italy, was also allowed to treat patients with ADA-SCID for whom other therapies had failed. Five patients have been treated in that trial, and not one has developed cancer.

The first SCID study to be resumed in the United States is led by Harry Malech and Jennifer Puck of the National Institutes of Health at Bethesda, Maryland. They were cleared to begin their trial in December and treated one child with X-linked SCID in January. So far, his condition is stable, Malech says.

The other two US trials are led by Kohn and by Kenneth Weinberg, both of the Childrens Hospital Los Angeles. Both say that they are consulting with the FDA and hope to resume their trials later this year.

Since 2002, scientists have learned more about why gene therapy caused the X-linked SCID patients to get cancer. Such patients receive a copy of a gene they lack, called the gamma-C gene. This gene allows their immune cells to grow normally. But in the children who get leukaemia, gamma-C seems to switch on a cancer-causing gene called LMO2, which is found in human DNA.

Fischer and other scientists will adjust their treatment plans to minimize risks from this switching effect. For instance, in most cases Fischer will now only treat children older than 6 months, because they might be less vulnerable to cancer than the very young babies who developed cancer in his trial. Fischer will also place an upper limit on the number of corrected cells he injects into the children.

Some researchers take a different tack when balancing the risk of cancer against potential cure. Weinberg is asking the FDA to allow him to resume his X-linked SCID trial without limiting the age of the children enrolled or the dose of cells they receive. But like all other leaders of SCID trials in the United States, Weinberg will monitor each of his patients for signs of cancer for at least a decade after the trial.




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© 2004 Nature Publishing Group
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Nature Science Update

Cure hoped for Huntington’s sufferers
Gene therapy succeeds in mice with brain disease.
9 June 2004
ERIKA CHECK


Gene therapy could ease the symptoms of some devastating brain disorders, according to evidence presented to US conference last week.

Many neurodegenerative diseases are caused when the brain makes mutant proteins that build up in the brain, causing gradually worsening symptoms. These brain-wasting diseases are devastating and incurable. They include Huntington’s disease, which affects around 250,000 people in the United States.

Beverley Davidson of the University of Iowa in Iowa City and her colleagues hope that gene therapy will help treat such diseases. The approach involves trying to correct genetic abnormalities by injecting an animal or person with corrective sequences of DNA or RNA.

The researchers tested their therapy in mice with a disorder that mimics a disease called spinocerebellar ataxia type 1, which leaves sufferers progressively less able to walk.

The therapy eliminated pockets of damaged brain tissue from the mice and corrected the physical symptoms of the disease.

Dominant defect

This is the first time that gene therapy has been shown to cure a disease like spinocerebellar ataxia. But the finding is also significant because it is the first time that gene therapy has been used to cure a so-called dominant progressive brain disorder. Such diseases occur in cases where a patient inherits a defective copy of a gene from just one parent.

Most gene therapy involves replacing a missing gene sequence. But in dominant disorders it is the mutant sequence itself that causes the problem, so any therapy needs to actively block a sequence rather than just replacing one.

To do this in the mice, Davidson’s team used a technique called RNA interference. The researchers isolated pieces of genetic material that bind to and block the mutant gene. They packaged these into stripped-down virus particles and injected them into the mice. The virus used was an adeno-associated virus that does not cause disease in mice or people.

After the injections, the proteins created by the mutant gene disappeared and the mice seemed to improve, the researchers told the annual meeting of the American Society of Gene Therapy in Minneapolis, Minnesota last week.

Davidson and her co-workers also reported at the meeting that RNA interference stopped human cells in culture dishes from producing the mutant proteins found in Huntington’s disease. For this work, they used a different virus to deliver the RNA to cells. The virus is similar to human immunodeficiency virus (HIV), but infects cats. The team took out all the infectious parts of the virus and replaced them with the pieces of therapeutic RNA.

Davidson says she hopes that her technique will move quickly into clinical trials. “The data are very promising; we hope we will be able to use RNA interference as a therapy for dominant neurodegenerative diseases.”


© Nature News Service / Macmillan Magazines Ltd 2004