Gene Therapy to Treat Disease - Biotechnology and Your Health: Pharmaceutical Applications - page 89

DNA viruses, can be engineered to insert small DNA sequences
into a cell's genome. Both adenovirus and adeno-associated
viral vectors can withstand injection into the body. These
vectors do have drawbacks, though. Adenovirus vectors can
cause dangerous reactions of tissue swelling and damage.
Adeno-associated vectors may cause damaging rearrangements
of chromosomes.
DNA alone, or trapped inside a small fatty balloon that will
melt into the cell's outer membrane, is also a possible vector. These
vectors can carry large payloads, but because they do not include
the viral genetic information, they are not very good at actually
delivering the genetic material.
PROBLEMS WITH GENE THERAPY
The idea of gene therapy has fostered great hope and not a little
hype because it seems to promise precise, effective, and long-
lasting treatments for devastating diseases in children and adults.
Unfortunately, as with many new technologies, the idea and the
reality are sometimes very far apart. Just because a vector “works”
in a test tube—meaning that the gene gets into the cells and the
new protein is produced—does not mean that it will successfully
cure a patient of a genetic disease. First, the engineered vector has
to get to the right part of the body. It is not simple to get a large,
complicated gene therapy vector to the exact spot that needs help,
so the earliest human trials of gene therapy were targeted at
diseases in which affected cells were accessible or, even better,
could be removed from the body, engineered, and then returned
to the patient. In 1990, Ashanti de Silva, the 4-year-old girl
with inherited immunodeficiency resulting from the absence of a
functional adenosine deaminase ( ADA ) enzyme, was given back
her own T cells that had been engineered with a retroviral vector
containing a gene for ADA, an enzyme required to break down
chemicals that are lethal to certain immune system cells. Over