FUNDAMENTAL BUILDING BLOCKS 323
Introducing new genes
Genes can be introduced into
diseased parts of the body by a
vector—a particle that “carries” the
gene to its source. Researchers
investigated several possibilities for
entities that might act as a vector—
including viruses, which are more
deficiency condition, known as
bubble-boy disease. Sufferers of
this condition are so susceptible
to infection that they may have to
spend their whole lives in a sterile
environment, or “bubble.”
Anderson’s team took sample
cells from the two girls, treated
them with the gene-carrying virus,
then transfused the cells back
into the girls. The treatment was
repeated several times over two
years—and it worked. However,
its effects were only temporary,
since new cells made by
the body would still inherit the
malfunctioning gene. This
remains a central problem for
gene therapy researchers today.Future prospects
Remarkable breakthroughs have
been made in the treatment of other
conditions. In 1989, scientists
working in the US identified the
gene that causes cystic fibrosis.
In this condition, defective cells
produce sticky mucus that clogs
lungs and the digestive system.
Within five years of identifying
the defective gene responsible,
a technique had been developed
to deliver healthy genes using
liposomes—a type of oily droplet—
as a vector. Results from the first
clinical trial are due in 2014.
Considerable challenges still
remain to be overcome to extend
gene therapy. Cystic fibrosis is
caused by a defect in just one gene.
However, many conditions with
a genetic component—such as
Alzheimer’s, heart disease, and
diabetes—are caused by the
interplay of many different genes.
Such conditions are far harder to
treat, and the search for successful,
safe gene therapies is ongoing. ■Gene therapy is ethical
because it can be supported
by the fundamental moral
principle of beneficence: it
would relieve human suffering.
William French
Anderson
See also: Gregor Mendel 166–71 ■ Thomas Hunt Morgan 224–25 ■ Craig Venter 324–25 ■ Ian Wilmut 326
normally associated with causing
disease, rather than fighting it.
Viruses naturally invade living
cells as part of their infection
cycle, but could they perhaps carry
the therapeutic genes with them?
In the 1980s, a team of
American scientists including
William French Anderson
succeeded in using viruses
to insert genes into cultured
(laboratory-grown) tissue. They
tested it on animals that suffered
from a genetic immune deficiency
disease. The goal was to get the
therapeutic gene into the animals’
bone marrow, which would then
make healthy red blood cells and
cure the deficiency. The test was
not very effective, although the
procedure worked better when
white blood cells were targeted.
In 1990, however, Anderson
performed the first clinical trial,
treating two girls who both
suffered from the same immuneScientists use viruses as a
vector to introduce healthy
genes into a patient’s cells.- Cells containing the
defective gene are taken
from the body. - A virus is
modified so that it
cannot reproduce. - The healthy
gene is
inserted into
the virus. - The virus is mixed
with cells from
the body. - The cells are
genetically altered
by the virus. - The healthy cells
are injected into the
body, where they
work normally.