Word: ada
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...work is based on the landmark experiment performed in 1990 by NIH Drs. W. French Anderson, Michael Blaese and Kenneth Culver on two Ohio girls, ages 4 and 9. Neither child was producing ADA, an enzyme that rids the bloodstream of harmful metabolic products. The absence of ADA can cause SCID by allowing toxic substances to accumulate and destroy immune-system cells. Both children had been kept alive by weekly injections of PEG-ADA, a costly synthetic enzyme, but neither was in good health...
...first approved gene-therapy trials, the pioneering NIH team extracted immune-system T cells from the Ohio girls, inserted normal ada genes into the cells and reinjected them. As the team had hoped, the T cells began churning out natural ADA, enabling the children's immune systems to function effectively. While that result marked the first successful treatment by gene therapy, it was not a cure; the altered T cells die out after several months, and the little patients must return to the NIH periodically to repeat the procedure...
Seeking a cure, researchers have now focused on so-called stem cells -- long-lasting cells that continually give rise to fresh blood cells. If ADA genes could be inserted into the parent stem cells, the scientists reasoned, the genes would be passed on to all newly formed immune cells, including T cells, and the patient would be ensured a permanent supply of the enzyme. But stem cells are rare, and most of them reside in the bone marrow...
Anderson, then at the NIH, with colleagues Dr. R. Michael Blaese and Dr. Kenneth Culver, extracted T cells from the little girl's blood and exposed them to a mouse-leukemia retrovirus that had been rendered harmless and endowed with a normal ADA gene. Invading the T cell, the retrovirus acted as a vector, depositing its genetic material, including the ADA gene, in the cell nucleus. After the re-engineered T cells were cultured, a process that produced billions of them, they were infused back into the child's bloodstream, where their new gene began producing the ADA enzyme...
...years after that historic experiment, Anderson reported to the Cold Spring Harbor symposium, both this child and another young Ohio girl who began the same treatment a few months later have acceptable levels of the ADA enzyme and are leading normal, healthy lives, needing only to return every six months for repeat treatments. This study, and one conducted by the University of Michigan's Dr. James Wilson on a woman with familial hypercholesterolemia, represent the only gene-therapy treatments to date with beneficial results. But Anderson expects more success from other projects getting under...