Gene Therapy to Treat Disease - Biotechnology and Your Health: Pharmaceutical Applications - page 90

the next 23 months, Ashanti received 10 more treatments, plus
the weekly injections of cow ADA linked to polyethylene glycol
(PEG-ADA) she had already been getting. Did the gene therapy
succeed? It is hard to tell. Twelve years after her first gene treat-
ment and ten years after her last, she appeared to be doing well,
and about 20% of her T cells carried the ADA gene. However,
based on lab tests, her immune cells are not working well. She still
receives PEG-ADA every week.
Stop and Consider
Why do you think there was so much initial excitement about
gene therapy?
Cystic fibrosis (CF), an inherited condition affecting the lungs
and other organs, is another genetic disease targeted by early gene
therapy efforts. In 1989, researchers identified the defective protein
that leads to CF, a protein that normally moves chloride into and
out of cells, and controls the movement of other molecules across
the cell's outer membrane. In CF patients, the cells lining the
passageway that carries air into the lungs produce mucus so thick
that the lungs become clogged, making breathing difficult and
infections frequent. Pancreas cells also do not work correctly in
people with CF, failing to deliver enzymes that break down food.
The air passage cells were a reasonable first place to test gene
therapy in CF patients, because nose drops and sprays could deliver
the vector, and the cells could be checked by a simple biopsy to
see if the vector got into the cells and produced the correct CF
protein. Unfortunately, despite great efforts to design a CF gene
therapy vector, and after at least 19 clinical trials, no satisfactory
vector has been found that can provide safe and reasonably stable
production of the normal protein in airway cells. Research continues;
at least scientists now know many approaches that do not work.