Genetic Enhancement - Brutes or Angels: Human Possibility in the Age of Biotechnology - page 159

ies of the malfunctioning gene (along with its adjacent regulatory DnA) to
these cells, and then reintroduce the cells into the patient (fig. 6.2). recall
that somatic cells are body cells, as opposed to germ cells (eggs or sperm).
Genetic alterations to somatic cells are not passed on to future generations,
and the alterations disappear when the person dies.
somatic cells chosen to be genetically altered are often adult stem cells
that will give rise to normal versions of the malfunctioning cells after be-
ing reintroduced into the patient. for example, engineering bone marrow
stem cells is a suitable approach for treating leukemias and other geneti-
cally caused blood diseases. The most common way of inserting new genes
into living cells is to use an inactivated virus as a carrier. such viruses are
called vectors. scientists and biotechnicians select an appropriate vector,
insert the normal human gene into vector DnA, and then expose the pa-
tient's cultured cells to thousands of vector particles carrying the normal
gene. The vectors enter the cells, and some of the normal genes they carry
become permanently incorporated into the DnA of the host cells.
A viral vector is not the only way to deliver new DnA into a cell's ge-
nome. large quantities of a normal gene can also be injected directly
into the affected tissue. By a poorly understood process, some of the in-
jected genes traverse cell membranes and enter cell nuclei, where they be-
come active. Genes may also be delivered to cells inside membrane-bound
vesicles called liposomes (fig 6.2). When a liposome fuses with the outer
membrane of a cell, it empties its genetic cargo into the cell's cytoplasm.
some of the genes then find their way into the nucleus and become active.
Adding normal genes to cells to compensate for abnormal genes is not
the only approach to somatic cell gene therapy. Abnormal genes may also
be deleted and then replaced or repaired, much more difficult procedures
than simply adding a gene at an unspecified location in the genome. Gene
replacement or repair has not yet been done in humans. But in 2011 a new
genetic engineering technology, zinc inger-mediated gene therapy, suc-
cessfully inactivated a specific gene in immune system cells of hiv pa-
tients. Clinical trial results demonstrated the technology's potential for
treating AiDs and curing certain genetic diseases (sharp 2011). finally, an-
other technology functionally equivalent to gene deletion, called RNA in-