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基因疗法被用于改善视力

更新时间:2014-1-16 20:47:32 来源:华尔街日报中文网 作者:佚名

Gene Therapy Technique Cited in Improving Vision
基因疗法被用于改善视力

Scientists have improved the vision of a small number of patients suffering from a rare and incurable eye disease by replacing a defective gene with a healthy one-a boost for a technique known as gene therapy.

The patients have choroideremia, a degenerative disease caused by defects in a single gene that leads to blindness and affects 1 in 50,000 people. In an early-stage trial published Wednesday in the Lancet, the researchers used a deactivated virus to safely ferry billions of healthy, lab-made versions of the gene into the retina. That appeared to restore the function of light-sensitive cells, which the disease impairs.

'We were surprised by the magnitude of vision improvement' in the patients, said Robert MacLaren, a professor of ophthalmology at the University of Oxford in England and leader of the clinical trial.

The experiment marks one of the first times that gene therapy has targeted the main light-sensing cells in the retina. It thus offers a possible route for treating far more common causes of blindness that affect the same cells, such as retinitis pigmentosa and age-related macular degeneration.

Gene therapy involves the use of DNA, rather than a protein or drug, to treat an ailment. The idea is that if the DNA gets properly embedded in the target cells, it can potentially remain there indefinitely and deliver benefits for a long time.

Gene therapy fell out of favor after a handful of early studies led to cancer and death. That's a big reason why it hasn't yet led to a single authorized treatment in the U.S.

Now, the technique is making a comeback. For example, in three early-stage clinical trials done a few years ago, the technique was used against a retinal disease called Leber congenital amaurosis. And in November 2012, European regulators approved a gene therapy treatment for a rare condition that leaves patients unable to properly digest fats-the first such approval in the Western world.

The ailment treated in the Lancet study, choroideremia, is caused by defects in a single gene on the X chromosome and mainly affects boys. Many start losing night vision by age 10 and become legally blind in their 40s.

Because of the defective gene, light-sensitive cells in the retina slowly stop working and then die. Prof. MacLaren's team decided to make healthy versions of the gene in the lab, load each onto a small virus (one that doesn't cause disease in people) and inject the mix under the retina.

The therapy is given in one eye so it's easy to compare the progression of the disease with the untreated eye. 'Every injection has 10 billion viral particles, each carrying one copy of the gene,' said Prof. MacLaren. 'We have to target millions of cells.'

The trial began with six patients. Two still had excellent visual acuity-clearness of vision-which is measured by reading lines of letters on a sight chart. Two other patients had good acuity and two had reduced acuity.

Six months after the operation, the two patients with reduced acuity showed improved vision, being able to read two and four more lines on the sight chart. The others could see better in dim light. The gains were sustained over several months of follow-up.

A 65-year-old in the trial said that when he now watches a soccer game on TV the 'green of the pitch is brighter and the numbers on the shirt much clearer.' Another who went through the procedure says he can now see stars in the night sky, which he hadn't seen for a long time.

Altering a patient's DNA is risky because it can trigger dangerous side-effects. In this case, there was no sign of an immune reaction in the first six months of the follow-up, according to the Lancet study.

The scientists hope to treat patients before their sight falters. 'We want to preserve the vision they've got,' said Prof. MacLaren. He now plans to test the technique on a larger group of about 30 patients.

通过将有缺陷的基因替换成健康的基因,科学家已经使少数患有一种罕见、难愈眼病的病人改善了视力。这对一项被称为基因疗法的技术是个推动。

上述病人患有脉络膜缺失症。这是一种由单一基因缺陷造成的退化性疾病,会导致失明,每50,000人就有1例。医学期刊《柳叶刀》(Lancet)周三刊登了初步试验的结果。在试验中,研究人员使用了一种失去活性的病毒来携带实验室制作的健康基因,将数以十亿计的这类基因安全地注入视网膜。这在表观上恢复了疾病损害的感光细胞的功能。

英国牛津大学(University of Oxford)眼科学教授、上述临床试验的负责人麦克拉伦(Robert MacLaren)称,病人视力的改善程度出乎意料。

这是以视网膜主要感光细胞为目标开展基因疗法的首批试验之一,由此可能给治疗影响主要感光细胞的更常见失明症(比如色素性视网膜炎和老年黄斑退化)提供一条途径。

基因疗法使用DNA治疗疾病,而不是使用蛋白质或药物。这种疗法的思路是,在被妥善嵌入目标细胞的情况下,DNA可能会永远留在细胞中,从而给病人带来长期的益处。

基因疗法一度失去关注,因为一些早期研究曾经导致癌症和死亡。这就是美国还没有批准任何一项基因疗法的重要原因。

现在这种技术正在重获关注。例如,在几年前完成的三项早期临床试验中,基因疗法技术被用于治疗一种名叫莱伯氏先天性黑蒙症的视网膜疾病。另一个例子是在2012年11月,欧洲监管机构批准用一项基因疗法治疗一种导致病人不能有效消化脂肪的罕见症状,开启了西方世界批准基因疗法的先例。

《柳叶刀》上发表的研究治疗的脉络膜缺失症是由X染色体的单一基因缺陷引起的,主要患者为男孩。许多患者在10岁时开始失去夜视力,在40岁-50岁时变得彻底失明。

受基因缺陷影响,视网膜中的感光细胞会慢慢地停止工作并死亡。麦克拉伦教授的团队决定在实验室制作健康的基因,并将每个基因都装进一个微小病毒(这种病毒并不会导致人类患病)中,然后将这种混合体注入到视网膜下面。

每个患者只有一只眼睛接受了这种疗法,因此通过未经治疗的那只眼睛,研究人员很容易就能对比病症的变化。麦克拉伦教授说,研究人员每次注入100亿个病毒颗粒,每个颗粒都携带一份基因。他说,我们需要将数以百万计的细胞作为目标。

试验是从六位病人开始的。其中两位病人仍拥有非常高的视敏度,两位病人拥有较高的视敏度,另外两位病人有着较低的视敏度。视敏度也被称为视觉清晰度,通过让病人阅读视力测验表上的字母来衡量。

术后六个月,两位视敏度较低的病人出现了视觉改善的现象,能够在视力测验表上多看清两到四行字母。其他病人在弱光环境下的视力也得到了增强。这种症状改善在随后的几个月内得以维持。

接受临床试验的一位65岁患者称,现在当他在电视上观看足球比赛时,绿色的场地更亮眼了,球衣上的号码也更清楚了。另一位接受手术的患者称,他很久都无法看到夜空中的星星,现在他能看到了。

改变患者的DNA是有风险的,因为这可能引来危险的副作用。《柳叶刀》上的研究显示,之后的六个月,患者并未出现有免疫反应的迹象。

这些科学家希望在患者彻底失去视力前进行治疗。麦克拉伦教授说,我们希望使患者现有的视力得到维持。他现在计划对约30位患者构成的更大群体测试这项技术。

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