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Exercise caution with powerful gene therapy

Alan Stahler

There are bacteria that, under ideal conditions of moisture, warmth and food, can reproduce every 20 minutes. Dividing unchecked, these microbes could engulf the Earth in no time at all.

Fortunately for us, conditions never remain ideal for long. Most commonly, microbes run out of food. Until they do, however, a bacterial population can grow wildly. An infection is simply a bacterial population exploiting abundant food while it can. The food is us.

Oozing over the pond mud, an amoeba engulfs a tidbit and digests it. Cells resembling such amoebae are even now slithering through our bodies, looking not for food but for alien invaders – bacteria, viruses, anything that might cause us harm. Finding their prey, they engulf and digest them. Such cells are part of the complex immune system vertebrates have shared for 500 million years.

HIV, the virus that causes AIDS, destroys some of the very cells that should protect us from viruses. The result – represented by the “I” in both “HIV” and “AIDS” – is “immunodeficiency,” destruction of the immune system.

The immune system identifies alien invaders with a sort of “lock and key” system. Immune cells produce a million or so differently shaped “locks.”

Some of these “locks” can bind to molecules within bacteria and viruses – the “keys.” Such a lock-and-key combination triggers the immune system into action.

The shapes of our immunological locks are determined by genes. Should an infant inherit a faulty gene, he might not be able to produce the locks needed to turn on his immune response. Such defects lead to problems, among them “bubble boy disease” – an inherited immunodeficiency. Unable to fight off the germs that surround us, most victims die early in infancy.

David, a Texas boy born in the late ’70s, survived for 12 years in a “bubble” – a chamber within which he received sterilized food, air, water, books, toys and clothing. (The gene responsible for the disease rests on the X chromosome, of which girls have two, but boys only one. With atYne working copy of the gene, girls are unlikely to develop bubble boy disease.)

The cells most immediately affected by the defective genes start out as immature stem cells. As they mature, the cells normally construct the “locks” that allow them to recognize invaders.

Researchers in Europe last week announced that they have engineered a virus to carry a good copy of the gene defective in “bubble boys.” They removed stem cells from victims of the disease and infected the cells with the engineered virus. Finally, they cultured the cells and re-inserted them into the boys’ bodies.

The treatment, so far, is working. The boys have working immune systems.

A caveat: Genetic engineering is not a precision operation. Viruses are notoriously profligate about where they insert their genes; inserting them in the wrong place can disrupt existing genes, or turn them on or off at the wrong time in the wrong place. Throwing such genetic switches has triggered cancers in lab animals.

Even as we cheer gene therapy’s first success, we need to acknowledge the extraordinarily powerful evolutionary forces with which we’re dealing.

In Britain, researchers must monitor the long-term health of subjects in gene therapy. And despite an informal moratorium on gene therapy that might affect sperm and eggs, such effects are always possible. Researchers are therefore required to monitor their patients’ offspring to the age of 16.

Trained as a biologist, Alan Stahler is also an amateur astronomer. He teaches biology and geology at Bitney Springs Charter High School. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).

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