1.   But it can work only if the healthy genes land in the right place.

2.   Defective genetic material can be replaced with healthy genes in patients suffering from immunological disorders, various cancers and metabolic diseases.

3.   In gene therapy, scientists try to use healthy genes to prevent or cure a variety of illnesses, from rare inherited disorders to heart disease and cancer.

4.   In gene therapy, scientists try to use healthy genes to replace ones that cause disease.

5.   In tests on rabbits and monkeys, the virus successfully carried a healthy gene into the target cells and caused no harmful effects.

6.   In two separate gene-therapy trials, the healthy gene has been successfully delivered to cells in the lungs and nose by a virus.

7.   In treating cystic fibrosis, one of the earliest diseases targeted with gene therapy, researchers are using the common cold virus to deliver healthy genes to damaged cells.

8.   The answer, the biologists have decided, is an infusion of healthy genes from Texas cougars.

9.   The technique of adding healthy genes to human cells, although still in its early stages, holds promise for treating a wide variety of diseases.

10.   Then there is the unrealized potential of gene therapy, the introduction of healthy genes to correct severe genetic diseases like cystic fibrosis or sickle cell anemia.