Despite an ongoing effort to increase worldwide public awareness of the importance of organ donations, there remains a serious shortage of viable human replacement organs. This shortage has led to increased efforts in xenotransplantation, the transplanting of animal organs into humans. The first such procedures were actually carried out in the early 20th century, when a pig’s kidney and a goat’s liver were implanted into two patients, neither of whom survived. The risks remain formidable; animals harbor viruses that, though relatively harmless to the animal, are potentially fatal to the human recipient. Some of these viruses are virtually unknown to modern science. But even a virus-free transplant can be rejected by the recipient, whose immune system will sense the presence of a foreign body, and will start producing white blood cells called lymphocytes to counter this new presence. Powerful drugs can suppress the immune system, but in so doing, they leave the body open to other infections.
There has been some progress in recent years. New drugs have been designed that suppress only certain aspects of the immune system. (A side benefit of research into these drugs is that they will likely help patients who have such immune system problems as arthritis and diabetes.) Even more promising is the research being made into genetically altering animal organs so that they will produce proteins that “fool” the human body into recognizing the transplanted organ as that of a human. And while doctors have not yet to see many long-term xenotransplant successes, the procedure has proven successful as a stopgap until a suitable human organ can be found. This has been true in a number of cases involving transplants of pig organs. (Pigs are especially suitable donors, as they have many organs that are about the same size as those of humans. In addition, there has been less ethical opposition to using pigs -- who are already bred for food -- than to using baboons, another animal whose anatomy is quite similar to ours.) Genetically changing only one of the pig’s 100,000 genes -- its alpha-gal gene -- produces proteins on the surface of the pig’s organs that are recognized as human by our immune systems.
To efficiently exploit genetic programming, researchers will need to combine it with cloning techniques, which can produce many animals with the same desirable genetic alteration. At that point, the organs can be removed from animals that “naturally” have the desirable traits. It is important to note, however, that even after suitable animal organs are readily available and more sophisticated anti-rejection drugs have been developed, the need for human donors will remain high into the foreseeable future.
1. According to the passage, genetically altering animal genes in transplanted organs can ____________.
A. aid in treating arthritis and diabetes
B. remove the alpha-gal gene
C. increase the effectiveness of the human body’s immune system
D. decrease the negative effects of certain viruses
E. affect the human immune response
2. The passage states which of the following about animal cloning in regard to xenotransplants?
A. It can never take the place of human organ transplants.
B. It will increase the human body’s ability to cope with animal viruses.
C. It will allow humans in need of new organs to survive until suitable human organs are available.
D. It will make genetic programming more practical.
E. It can increase the effectiveness of anti-rejection drugs.
3. All of the following are mentioned in the passage as a difficulty associated with animal organ transplants EXCEPT:
A. Animal organ transplants are rarely successful on a long-term basis.
B. Genetically altering an animal can produce proteins that the human body rejects.
C. There are ethical questions associated with using animals for purposes of xenotransplantation.
D. Convincing the human body to accept the implanted organ can be problematic.
E. Some animals have viruses that can prove fatal to humans.
参考答案：[hide=d30]EDB[/hide]