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  3. Cloned Pigs — the Potential Organ Donors Five cloned piglets, genetically modified so that their organs are much less likely

Cloned Pigs — the Potential Organ Donors Five cloned piglets, genetically modified so that their organs are much less likely

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问题     Cloned Pigs — the Potential Organ Donors
    Five cloned piglets, genetically modified so that their organs are much less likely to be rejected by a human donor recipient, have been born in the US.
    More than 62, 000 people in the US alone are waiting to receive donated hearts, lungs, livers, kidneys and pancreases. The number of human donors falls far short of demand. Pig organs are of a similar size to human organs, and some scientists hope they might be used to help meet the shortfall. But previous attempts to transplant unaltered pig tissue into humans have failed, due to immune rejection of the tissue.
    The five piglets, born on Christmas Day, lack a gene for an enzyme that adds a sugar to the surface of pig cells. The sugar would trigger a patient’s immune system into launching an immediate attack.
    " This advance provides a near-time solution for overcoming the shortage of human organs for transplants, as well as insulin-producing cells to cure diabetes," says David Ayares, vice president of research at PPL Therapeutics, US division, where the pigs were created. "This is the key gene for overcoming the early stage of rejection. "
    However, scientists warn that much more work is necessary before organs from copies of the pigs could be transplanted into humans. Human genes will need to be added, to prevent rejection of the organ in the long-term. There are also concerns that pig viruses could infect organ recipients.
    Cloning techniques were vital to the production of the pigs. Genes can only be knocked out in a single cell. Cloning of these single cells then allowed the creation of a whole animal in which the gene was knocked out in every cell. But the PPL researchers have succeeded in knocking out only one copy of the gene for the enzyme, called alpha 1, 3 galactosyl transferase. The team will now attempt to knock out both copies of the gene.
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答案 克隆猪有望成为人体器官移植供体 在美国已出生了五只转基因的克隆小猪，它们的器官在植入人体时发生排异反应的可能性大为减小。 仅在美国就有6．2万多人在等待他人捐献心脏、肺、肝脏、肾脏和胰脏。捐献器官的人数远远供不应求。猪的器官与人体器官大小差不多，一些科学家希望它们可用于补足这一短缺。但是，由于组织免疫排异反应，以前用未经改良的猪器官进行的移植尝试都失败了。 圣诞节出生的这五只小猪，缺少一种酶基因，该基因可使猪的细胞表面增加某种糖类物质。这种糖会引发病人的免疫系统立即发动攻击。 这些小猪是由PPL医疗公司美国分公司培育出来的，该公司研究部副总裁大卫-阿亚里斯说：“这项进展及时解决了人体移植器官的短缺问题，也解决了胰岛素分泌细胞的短缺问题，该细胞用以治疗糖尿病。这是克服早期排异反应的关键基因。” 但是，科学家提醒说，在克隆猪所提供的器官能顺利植入人体之前，还有大量的工作要做。为了防止长期的排异反应，还要加上人类基因。猪的病毒会感染器官接受者，也是要人们关注的。 克隆技术是培育这些猪的关键。去除基因只能在单个细胞中进行。克隆这些单细胞后再培育出一头猪，该猪身上的每个细胞中的该基因都被去除了。但是PPL公司的研究人员只是成功地去除了产生这种叫做α1，3半乳糖转移酶的基因的一个复制品。他们正试图将这个基因的两个复制品都加以去除。
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