Although scientists have been working on gene therapy
technology since the 1960s, companies are now able to commercialize gene
therapy as a way to treat rare genetic disorders. After the death of a patient
in a clinical trial of gene therapy for a liver disease in 1999, new gene
therapies using safer and better viral vectors for the delivery of genes into
cells have been used. In 2016, Europe approved Strimvelis, a gene therapy
treatment that is used to cure children with a form of Severe Combined
Immunodeficiency (SCID) known as Adenosine Deaminase (ADA) deficiency. This
disease is abbreviated as ADA-SCID.
is an autosomal recessive disease that affects 1 in every 200,000 to 1,000,000
babies (“Adenosine Deaminase Deficiency”). Adenosine deaminase, which is the
molecule that patients with ADA-SCID are deficient in, is important in
regulating the amount of deoxyadenosine in the body. Deoxyadenosine is
poisonous to lymphocytes, which constitute T cells, B cells, and natural killer
(NK) cells. Deoxyadenosine is made when DNA is degenerated. The role of
adenosine deaminase is to break down deoxyadenosine into the non-poisonous
molecule deoxyinosine. Patients with ADA-SCID have a mutation in the ADA gene
that causes adenosine deaminase to not be made at sufficient levels, or not at
all. Because of the mutation, adenosine deaminase builds up in the body to a
point that is lethal to lymphocytes.
of the killing of the lymphocytes, ADA-SCID patients do not have enough white
blood cells circulating in their blood. The other cells of the immune system
are not affected by the presence of deoxyadenosine, but the lymphocytes play a
large and important role in a functional immune system. NK cells have a role in
innate immunity, in which they cause infected cells (especially
virally-infected cells) to die. The T cells have many functions, such as
activating B cells and causing infected cells to die by apoptosis. The B cells
differentiate into plasma cells, which are important in secreting antibodies. This
results in the patients not being able to amount an immune response to
pathogens that normally-functioning immune systems would be able to easily
eradicate. Therefore, patients with ADA-SCID usually do not live longer than
is a treatment for ADA-SCID patients in which the faulty gene is replaced with
a functioning gene, the definition of gene therapy. A virus will be used to
deliver the functioning gene by having been engineered to carry the functioning
ADA gene in its genome. The way Stremvelis brings the functioning gene into the
patient is by an ex-vivo technique. The bone marrow of the ADA-SCID patient
will be extracted and then infected with the modified viruses. During
infection, the virus will have to inject its genome into the genome of the bone
marrow cells in order for the bone marrow cells to receive the functioning
gene. After this process has taken place, the modified cells are introduced
back into the patient by an infusion drip into the vein (Mullin, “A Year After
gene therapies are now becoming a reality. In this past year, Stremvelis, which
is administered in Milan, Italy, was used commercially to treat an ADA-SCID
patient, rather than in a clinical trial. However, since gene therapies are a
novel technology, with it comes a hefty billing price. Stremvelis is available
to patients at a price of $648,000. Also, because it is only administered in
Italy, patients across Europe will have to fly to Italy to receive treatment. Nevertheless,
the commercialization of different gene therapies will pave a road in which any
disease, not just rare ones, can be cured by this method.
“Adenosine Deaminase Deficiency.” National
Institutes of Health, U.S. Department of Health &
Human Services, 28 Nov.
2017. Accessed 29 Nov. 2017.
Mullin, Emily. “A Year After Approval,
Gene-Therapy Cure Gets Its First Customer.” MIT
Review, MIT Technology Review,
3 May 2017. Accessed 29 Nov. 2017.
_____. “Gene Therapy 2.0.” MIT
Technology Review, MIT Technology Review, Mar.
Accessed 29 Nov. 2017.