Jellyfish Advance Gene Therapy Research
Natural Fluorescent Ability of
Jellyfish Provides New Way To
Test Gene Therapy Transfer Technology
Toronto researchers have used a jellyfish gene inserted in a retroviral
vector -- a gene therapy delivery vehicle -- to develop an improved method
to introduce recombinant genes into human blood cells. The green fluorescent
protein (GFP) gene found in fluorescent jellyfish also provides an easy
way for researchers to identify and follow the genetically-modified cells.
The findings, the result of a joint effort of a research team led by Dr.
Robert Hawley, Scientific Director, Oncology Gene Therapy Program at The
Toronto Hospital and Associate Professor, Medical Biophysics and Medicine,
University of Toronto, in collaboration with scientists in the United States,
are published today in the British journal, Gene Therapy.
The key to success for any gene therapy treatment is to devise a vector
that is a safe and efficient delivery vehicle. The vectors are viruses,
rendered neutral, without the ability to replicate themselves. But more
importantly, they are also altered to carry genes of interest -- therapeutic
genes -- that, in theory, when introduced into humans begin to express themselves
and function to correct a genetic defect.
The Hawley team pursued the idea of modifying a retroviral vector it had
previously created based on research which suggested that there may be a
problem when more than one gene is carried by the vector. (The vector usually
carries a drug-resistance gene in addition to the therapeutic gene.) Current
vectors have been shown to be inefficient in gene therapy trials to date,
possibly because they shut off due to "competition" between the
two genes.
"Previous research suggested that one gene
may down-regulate the other in the vector resulting in inefficient expression,"
Dr. Hawley says. "However, by using the GFP gene as a surrogate therapeutic
gene we were able to rapidly test several retroviral vector configurations.
This allowed identification of one vector that efficiently expressed both
genes. It was gratifying to find that the vector, which gave much higher
levels of expression than we had seen before, was the one in which we eliminated
any possibility of gene competition, by physically linking the GFP gene
to the drug-resistance gene."
An added benefit of the finding was that the glow of the fluorescent jellyfish
gene from the retroviral vector was so strong that it provided an extremely
simple way to measure gene transfer, just by looking at the cells under
a microscope. "It is really spectacular. Under the microscope the GFP
gene-containing cells shine bright green," Dr. Hawley explains.
This research was conducted in collaboration with the biotechnology firm,
SyStemix/Novartis, located in Palo Alto, California, as a prelude to stem
cell gene therapy, a possible treatment for inherited blood diseases.
Dr. Hawley and his team will continue to test and modify the new vector
with the goal of taking it to the clinical stage. In the meantime, the original
vector, without the GFP gene, will be used in a clinical trial starting
in January at the Indiana University School of Medicine, Department of Pediatrics
and Medical and Molecular Genetics. This gene therapy trial will evaluate
the earlier vector in children with an inherited immunodeficiency disease.
In a second paper published in the same journal today, Dr. Hawley's team
took the original vector it modified with the GFP gene and altered it in
a different way to express a therapeutic gene to create a potential vaccine
for skin cancer.
"We found that this particular vector design expressed immunostimulatory
molecules like interleukin-6 at 10 to 30 times the level which previously
resulted in the shrinking of tumours in a mouse model of skin cancer,"
Dr. Hawley says. (Interleukin-6 is one of many interleukins in the body
that play a role in stimulating the immune system.)
"The challenge now in cancer gene therapy research, besides obtaining
sufficient funds to be able to manufacture the clinical grade vaccines required
for immunotherapy trials, is to find the right combination of interleukins
that will induce a strong enough immune response in humans so as to completely
eradicate their tumours," Dr. Hawley says.
Both research studies were funded in part by the National Cancer Institute
of Canada.
For more information, contact Josey Panetta,
Senior Media Relations Officer, The Toronto Hospital and Princess Margaret
Hospital, 416-340-3303.