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3. _____? There was news this week of a successful attempt to correct a faulty gene that leads to blindness. An international
team of scientists, led by a group at the University of Pennsylvania, used a genetically engineered virus to introduce the correct
version of a gene called
RPE65
into six people suffering from a retinal disease known as Leber's congenital amaurosis. In four
patients vision improved. Earlier work with the same technique on dogs suffering from a naturally occurring form of blindness has
also been successful.
4. _____ in Maryland, and one of the directors of the study, reported in
The New England Journal of Medicine
, reckons the
treatment could be used more widely. It offers hope for correcting any of the ten genetic defects that can cause Leber's, as well as
some forms of retinitis pigmentosa, a group of genetic eye conditions.
5. _____, it adds to the rather small number of human successes with gene therapy. The first human gene-therapy trial was in
1990, on a rare and severe immunodeficiency disease known as SCID. Although questions remain about whether the first examples
were as successful as claimed, the treatment has since been used successfully on over two dozen patients around the world.
The clinical approach
6. ______ for other conditions is proceeding. For diseases such as cystic fibrosis or muscular dystrophy, which involve one or a
few inherited genetic changes, clinical trials are attempting to introduce the correct versions of faulty genes into patients. For acquired
diseases, such as cancer, gene-therapy trials are introducing genes that are intended to kill cancerous cells. Len Seymour, a researcher
at Oxford University, likens this approach to using DNA as a drug.
7. ______, people wrongly thought that it would be easy to introduce genetic material into diseased cells. He likens attempts by
researchers to introduce genes to "throwing a carburettor on to the passenger seat of a car and expecting the car to go".
8. ______, so far, have been with diseases where it is relatively easy to introduce genes. In SCID, for example, bone-marrow
precursor cells can be removed, treated and then injected back into place. In the case of Leber's congenital amaurosis, viruses carrying
the correct gene can be injected directly into the retina where they will infect retinal cells. Direct injection is also being used in gene-
therapy trials on patients with Parkinson's and on those with muscular dystrophy.
9. ______ problems have been with the vector that carries the gene, usually a virus. Sometimes these viruses have provoked
strong immune reactions – which is what caused the death of Jesse Gelsinger, an 18-year-old American who had a damaged gene that
prevented his liver from making an enzyme to break down ammonia. In 1999 he was the first person to be publicly identified as
having died in a clinical trial for gene therapy.
10. ______ cause genetic mutations when they integrate themselves into human DNA. Of the 27 people treated for SCID
worldwide, four have developed leukaemia and one has died, says Dr Seymour, though this needs to be balanced against the fact that
most children with SCID are completely lacking a normal immune system and die in early childhood.
11. ______ on improving the viral vectors. One way of doing this is to create viruses that lose their ability to activate local genes
when they are integrated into their host's genome. Another route, used in the recent Pennsylvania trial, is to use viruses that integrate
themselves only into the cell, rather than the cell's DNA. And at Oxford Dr Seymour is working on "stealth viruses", which are coated
in a polymer that hides the virus from the immune system. This allows the modified virus to circulate for longer in a patient's blood
stream and thus have a better chance of getting to tumours disseminated around the body. Across the world a number of groups are
trying to develop synthetic polymers to deliver genes, entirely removing the need to use viruses.
12. _____ is centred on cancer. One approach, used by Shenzhen SiBiono GeneTech, a Chinese company, is to replace broken
tumour-suppressor genes with the correct version. In 2003 the company's treatment for head and neck cancer, which accounts for
about 10 % of the 2.5 m new cancer patients in China every year, gained the first commercial approval of a gene-therapy treatment.
Yet many outside China have been dismissive of the quality of the data used to support this therapy, although Dr Seymour says that
when used with chemotherapy in some situations, it can be good.
13. _____, one that is on the fringes of what strictly you would call gene therapy, is "virotherapy". This uses viruses selectively
to attack only cancerous cells. There are about a dozen trials in this area. In 2006 researchers from the Hebrew University in Israel
isolated a variant of the virus that causes Newcastle disease, a highly contagious disease in birds that can kill. This variant was able to
target selectively cancer cells in humans. Trials on a form of aggressive primary brain tumour have shown one complete regression
out of 14 treated patients.
14. _____, Dr High says she is optimistic about the future of gene therapy. She argues that treatments only really got going 15
years ago (when the SCID trials began). This, she adds, should be put into context: the development of bone-marrow transplantation
or monoclonal-antibody treatments both took several decades. Drugs that are "biologics", such as vaccines, monoclonal antibodies
and gene therapy, are derived from biological processes and are inherently more complicated than the chemicals that have
traditionally been the mainstay of the pharmacological arsenal.
15. _____ could be the most complex biologic of all, reckons Dr High. The work carried out so far gives scientists a reasonably
complete list of things that can go wrong. Dr High warns that researchers are still at the bottom of a tall ladder, though she expects
quicker progress in the future. "We have our foot on the rung, and it's not giving way."
A R T I C L E 10.
T a s k O n e. Make up questions covering the subject matter of the article.
T a s k T w o. Write a review on the article.
Of froth and fundamentals
Oct. 9
th
2008
From
The Economist
print edition
The real lesson from volatile commodity prices
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