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.

 克隆猪有望成为人体器官移植的供应者

      
在美国已诞生了5只基因改良的克隆小猪,这使得它们的器官在植入人体时产生排异反应的可能性大为缩小。

   
仅仅在美国就有6.2万多人在等待被捐献出的心脏、肺、肝脏、肾脏和胰脏,器官捐献者的人数远远满足不了要求。猪的器官大小与人的器官相似,一些科学家希望它们可用于弥补器官短缺问题。但是,由于种间组织免疫系统的相互排异反应,从前那些用未经改良的猪器官做的移植试验都失败了。

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."

　 
圣诞节出生的这5只小猪,缺少一种使猪的细胞表面加上某种糖类物质的酶的基因。正是这种糖引发病人的免疫系统立即产生免疫排异反应。

     
培育出这些小猪的PPL医疗公司美国分部的研究项目副总裁大卫·阿亚里斯说:"这项科研进展及时解决了目前所面临的人体器官移植来源短缺问题,以及治疗糖尿病所需的生产胰岛素的细胞。这是个解决早期排异反应的关键基因。"

 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 conerns 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.

　 
但是,科学家们提醒说,在由克隆猪所提供的器官能够顺利植入人体以前,还有很多必需的工作要做。可能会需要再加上人体的基因以使这些器官能够长期免于排异反应。猪的病毒对接受器官的人的感染,也是个值得关注的问题。

     
克隆技术是培育这些猪的关键。基因的去除只有在单个细胞中才能进行。克隆这些单细胞然后再将其培育成一只完整的动物,这样动物身上的每个细胞中的这种基因就都被去除了。但是,PPL医疗公司的研究人员只是成功地去除了产生这种叫α