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CREATING A WORKING GENE

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The gene transfer therapy begins when a working gene is The speciﬁc vectors used in gene
T
he speciﬁ

ect
ors used in gene
created in a laboratory. The working gene is developed to therapy are chosen because of their
therapy are chosen because of their
contain the instructions for making a needed protein.
ability to target appropriate cells within
Scientists design working genes to meet a disease’s the body. In gene transfer therapy

specific needs. For example, in patients with hemophilia A, for hemophilia A and B, vectors that
an F8 gene is needed to code for factor VIII protein, which target liver cells are being investigated
is essential for clotting, and in hemophilia B, an F9 gene is because these cells can make the
needed to code for factor IX protein.
proteins required for blood to clot.
BUILDING A
THERAPEUTIC VECTOR gene toward preferred cells where it can be
The working gene now has to be delivered into the body. used to make the needed proteins.
To do so, a therapeutic vector is created. This therapeutic
vector is created by modifying a naturally-occurring virus; Research is ongoing to determine the possible impact of
the shell of the virus is created without the viral DNA, and the therapeutic vector delivering the working gene to the
the working gene is put inside the empty shell. No longer other cells in the body. Once in the body, the new gene is
a virus, the therapeutic vector is designed to deliver the designed to do the work of the gene that is missing or isn’t
working gene to the cells in the body where it is needed. functioning properly. The goal is to provide instructions
for the body to make the protein it needs on its own, and
DETERMINING ELIGIBILITY ongoing research is evaluating the risks and impact of

As part of gene therapy research, a healthcare provider introducing the new gene.
must determine whether a patient is eligible. Because the new, working gene is not intended to become
Factors such as age, gender and liver health may be part of your DNA, the original missing or mutated gene is
considered. Therapeutic vectors being used in research left unchanged. Gene transfer is not designed to replace or
are commonly made from adeno-associated viruses edit the existing gene, which means that the mutated gene
(AAVs). These viruses are not known to make people could still be passed to future generations.
sick. They are found naturally around the world, so some
people will have already developed immunity to them via
exposure at some point in the past. Having preexisting MONITORING SAFETY
immunity to the AAV used by a gene therapy could reduce AND EFFICACY

or eliminate its effectiveness. Because of this, candidates
may have to be screened with a blood test to ensure that Regular monitoring after gene therapy is important
they do not have immunity. because it allows researchers to understand any risks and
what impact the gene transfer is having. Patients in clinical
trials meet with their care team for blood tests, and to
DELIVERING THE discuss their medication regimen and lifestyle to collect
WORKING GENE data as part of the study. As with all medications, response

Once the patient is determined to be eligible, the to gene therapy may vary. How long gene therapy might
keep working is being evaluated in ongoing clinical trials
gene therapy is ready for administration to evaluate its with researchers aiming to create a long-lasting therapy.
safety and effectiveness. A single, one-time infusion in an

appropriate clinical infusion setting delivers large numbers As of publication, no gene therapies for hemophilia A
of therapeutic vectors into the body. The therapeutic or B have been approved for use or determined to
vector is designed to both protect and guide the working

be safe or effective.

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