2012年雅思阅读考试考前冲刺试题（10）_第2页

8.Researchers have known for some time that viruses can kill tumour cells and some aspects of the work have already been published in scientific journals.American scientists have previously injected viruses directly into tumours but this technique will not work if the cancer is inaccessible or has spread throughout the body.

　　9.Prof Seymour's innovative solution is to mask the virus from the body's immune system, effectively allowing the viruses to do what chemotherapy drugs do - spread through the blood and reach tumours wherever they are.The big hurdle has always been to find a way to deliver viruses to tumours via the bloodstream without the body's immune system destroying them on the way.

　　10."What we've done is make chemical modifications to the virus to put a polymer coat around it - it's a stealth virus when you inject it," he said.

　　11.After the stealth virus infects the tumour, it replicates, but the copies do not have the chemical modifications.If they escape from the tumour, the copies will be quickly recognised and mopped up by the body's immune system.www.Examw.com

　　12.The therapy would be especially useful for secondary cancers, called metastases, which sometimes spread around the body after the first tumour appears."There's an awful statistic of patients in the west ...with malignant cancers; 75% of them go on to die from metastases," said Prof Seymour.

　　13.Two viruses are likely to be examined in the first clinical trials: adenovirus, which normally causes a cold-like illness, and vaccinia, which causes cowpox and is also used in the vaccine against smallpox.For safety reasons, both will be disabled to make them less pathogenic in the trial, but Prof Seymour said he eventually hopes to use natural viruses.

　　14.The first trials will use uncoated adenovirus and vaccinia and will be delivered locally to liver tumours, in order to establish whether the treatment is safe in humans and what dose of virus will be needed.Several more years of trials will be needed, eventually also on the polymer-coated viruses, before the therapy can be considered for use in the NHS.Though the approach will be examined at first for cancers that do not respond to conventional treatments, Prof Seymour hopes that one day it might be applied to all cancers.