2.  Gene therapy is a technique for
correcting defective genes responsible
for disease development

3.  A “normal” gene is inserted in the
genome to replace an “abnormal”
disease-causing gene
› A carrier molecule called a vector must be
used to deliver the therapeutic gene to the
patients target cells

4.  The most common vector used in gene
therapy is a virus
› Viruses have evolved a very effective way of
encapsulating and delivering their genes to
human cells in a pathogenic manner

5.  Retroviruses: a class of viruses that can
create double stranded DNA copies of
their RNA genomes
› These copies of their genomes can be
intergrated into the chromosomes of host
cells
› Human immunodeficiency virus (HIV) is a
retrovirus

6.  Adenoviruses: a class of viruses with
double stranded DNA genomes that
cause respiratory, intestinal and eye
infections in humans
› The virus that causes the common cold is an
adenovirus

7.  Adeno-assosiated viruses: a class of small
single stranded DNA viruses that can
insert their genetic material at a specific
site on chromosome 19

8.  Herpes simplex viruses: a class of double
stranded DNA viruses that infect a
particular cell type, neurons.
› Herpes simplex virus type 1 is a common
human pathogen that causes cold sores

9.  There are several non-viral options for
gene delivery, the simplest is the direct
introduction of therapeutic DNA into
target cells.
› This approach is limited because it can be
used only with certain types of tissues and
requires large amounts

10.  Immune response: the immune system is
designed to attack any foreign object
that is introduced to human tissues. This
risks stimulating the immune system and it
would reduce the effectiveness of the
treatment

11.  Problems with viral vectors: some issues
have arisen from the seemingly perfect
vector for gene therapy, they
occasionally are toxic and cause
immune and inflammatory responses.
› Scientists have also had issues with gene
control and targeting tissues
› Patients are also afraid that the viruses will
recover their ability to cause disease and
infect them.

12.  Overall viral gene vectors are the
simplest and easiest way to treat a
patient with gene therapy, but some
controversies arise that oppose them.
Scientists will continue working hard to
find better ways to use gene therapy
and sometime in the future we may be
able to cure a whole score of diseases
associated with genetics.