Medicine: Moving Toward Designer Genes

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Last spring's U.C.L.A. development has prompted similar questions, but the medical payoff from it may come a bit sooner. In that experiment, a team of scienlists led by Martin Cline and Winston Salser isolated genes that help produce an enzyme resistant to methotrexate, a drug used to treat cancer. The researchers added the genes to cell cultures of mouse bone marrow. The cells that picked up the foreign material, along with cells that had been incubated with genes that do not confer resistance, were then injected into mice whose own bone marrow had been destroyed. To see if the drug-resistance genes were working, the animals were given methotrexate. Tests after two months showed that cells that carried the resistance genes made up most of the bone marrow.

The U.C.L.A. findings may eventually help patients undergoing cancer chemotherapy. Methotrexate, used to treat leukemia and other cancers, is like most antitumor drugs: potent but harsh. It indiscriminately destroys rapidly proliferating cells, malignant and healthy alike. Among the healthy ones are those of bone marrow, which produce blood cells. The damage that methotrexate does to bone marrow effectively limits how much of it can be given to patients. Making the cells resistant to the drug's assault might give patients the ability to withstand more intensive therapy.

Researchers also speculate that doctors might use the technique to correct blood diseases that result from defects in single genes, including sickle-cell anemia and thalassemia. The therapeutic gene could be transferred into bone marrow cells along with a gene for drug resistance. Exposure to the drug would kill off marrow that produces defective blood cells and allow a population of "cured" cells to take over.

A5 more experiments with living animals get under way, the longstanding debate over genetic engineering's ethical implications and potential dangers is sure to intensify. Some scientists, like Rockefeller University's Norton Zinder, maintain that experimentation with humans is still a long way off and the concern is thus premature: "No one's going to diddle with human embryos in a time frame we can understand. Maybe in a thousand years."

Others are not so sure. Notes Harvard's Jonathan Beckwith: "What's happened in this field is a series of advances. When each happens, most people go around saying, 'The idea of genetically engineering embryos is so far off.' And then the next advance occurs. We may be moving faster than we think."

Reported by Suzanne Wymelenberg/New Haven and Rosemary George/West Berlin