Category Archives: Gene therapy

Gene therapy is designed to introduce genetic material into cells to compensate for abnormal genes or to make a beneficial protein. If a mutated gene causes a necessary protein to be faulty or missing, gene therapy may be able to introduce a normal copy of the gene to restore the function of the protein.

A gene that is inserted directly into a cell usually does not function. Instead, a carrier called a vector is genetically engineered to deliver the gene. Certain viruses are often used as vectors because they can deliver the new gene by infecting the cell. The viruses are modified so they cant cause disease when used in people. Some types of virus, such as retroviruses, integrate their genetic material (including the new gene) into a chromosome in the human cell. Other viruses, such as adenoviruses, introduce their DNA into the nucleus of the cell, but the DNA is not integrated into a chromosome.

The vector can be injected or given intravenously (by IV) directly into a specific tissue in the body, where it is taken up by individual cells. Alternately, a sample of the patients cells can be removed and exposed to the vector in a laboratory setting. The cells containing the vector are then returned to the patient. If the treatment is successful, the new gene delivered by the vector will make a functioning protein.

Researchers must overcome many technical challenges before gene therapy will be a practical approach to treating disease. For example, scientists must find better ways to deliver genes and target them to particular cells. They must also ensure that new genes are precisely controlled by the body.

A new gene is injected into an adenovirus vector, which is used to introduce the modified DNA into a human cell. If the treatment is successful, the new gene will make a functional protein.

The Genetic Science Learning Center at the University of Utah provides information about various technical aspects of gene therapy in Gene Delivery: Tools of the Trade. They also discuss other approaches to gene therapy and offer a related learning activity called Space Doctor.

The Better Health Channel from the State Government of Victoria (Australia) provides a brief introduction to gene therapy, including the gene therapy process and delivery techniques.

Penn Medicines Oncolink describes how gene therapy works and how it is administered to patients.

Next: Is gene therapy safe?

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How does gene therapy work? - Genetics Home Reference

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Gene Therapy

Challenges in Gene Therapy?

Gene therapy is not a new field; it has been evolving for decades. Despite the best efforts of researchers around the world, however, gene therapy has seen only limited success. Why?

Gene therapy poses one of the greatest technical challenges in modern medicine. It is very hard to introduce new genes into cells of the body and keep them working. And there are financial concerns: Can a company profit from developing a gene therapy to treat a rare disorder? If not, who will develop and pay for these life-saving treatments?

Let's look at some of the main challenges in gene therapy.

For some disorders, gene therapy will work only if we can deliver a normal gene to a large number of cellssay several millionin a tissue. And they have to the correct cells, in the correct tissue. Once the gene reaches its destination, it must be activated, or turned on, to make the protein it encodes. And once it's turned on, it must remain on; cells have a habit of shutting down genes that are too active or exhibiting other unusual behaviors.

Introducing changes into the wrong cells Targeting a gene to the correct cells is crucial to the success of any gene therapy treatment. Just as important, though, is making sure that the gene is not incorporated into the wrong cells. Delivering a gene to the wrong tissue would be inefficient, and it could cause health problems for the patient.

For example, improper targeting could incorporate the therapeutic gene into a patient's germline, or reproductive cells, which ultimately produce sperm and eggs. Should this happen, the patient would pass the introduced gene to his or her children. The consequences would vary, depending on the gene.

Our immune systems are very good at fighting off intruders such as bacteria and viruses. Gene-delivery vectors must be able to avoid the body's natural surveillance system. An unwelcome immune response could cause serious illness or even death.

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Challenges in Gene Therapy - Learn Genetics

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New research published online in Blood, the Journal of the American Society of Hematology (ASH), reports that children with "bubble boy disease" who undergo gene therapy have fewer infections and hospitalizations than those receiving stem cells from a partially matched donor. The research is the first to compare outcomes among children with the rare immune disorder -- also known as X-linked severe combined immunodeficiency (SCID-X1) -- receiving the two therapeutic approaches.

Children with SCID-X1 are born with a genetic defect that prevents them from developing a normal immune system. Because they are prone to life-threatening infections, infants with SCID-X1 must be kept in a sterile, protective bubble and require extensive treatment for survival beyond infancy. Infants with SCID are most likely to survive if they receive a stem cell transplant from a fully matched donor -- typically a sibling -- a procedure that replaces an infant's diseased stem cells with healthy donor cells. Following a successful fully matched transplant, infants with SCID-X1 are able to produce their own immune cells for the first time.

In the absence of a fully matched stem cell donor, infants with SCID-X1 may receive a transplant from a partial, or "half-matched," donor -- typically their mother or father. They may also undergo gene therapy, a much different approach. Gene therapy for SCID-X1 involves extracting an infant's own bone marrow, using a virus to replace faulty genetic material with a correct copy, and then giving "corrected" bone marrow back to the patient. Half-matched stem cell transplant and gene therapy represent secondary treatment approaches for infants with SCID-X1. Until recently, researchers had not yet compared outcomes among children treated with each respective approach.

"Over the last decade, gene therapy has emerged as a viable alternative to a partial matched stem cell transplant for infants with SCID-X1," said lead study author Fabien Touzot, MD, PhD, of Necker Children's Hospital in Paris. "To ensure that we are providing the best alternative therapy possible, we wanted to compare outcomes among infants treated with gene therapy and infants receiving partial matched transplants."

Dr. Touzot and colleagues studied the medical records of 27 children who received either partial-matched transplant (13) or gene therapy (14) for SCID-X1 at Necker Children's Hospital between 1999 and 2013. The children receiving half-matched transplants and the children receiving gene therapy had been followed for a median of six and 12 years, respectively.

The researchers compared immune, or T-cell, development among patients and also compared key clinical outcomes such as infections and hospitalization. Investigators observed that the 14 children in the gene therapy group developed healthy immune cells faster than the 13 children in the half-matched transplant group. In fact, in the first six months after therapy, T cell counts had reached normal values for age in more than three-fourths (78%) of the gene therapy patients, compared to roughly one-fourth (26%) of the transplant group. The more rapid growth of the immune system in gene therapy patients was also associated with faster resolution of some opportunistic infections (11 months in gene therapy group vs. 25.5 months in half-matched transplant group). These patients also had fewer infection-related hospitalizations (3 in gene therapy group vs. 15 in half-matched transplant group).

"Our analysis suggests that gene therapy can put these incredibly sick children on the road to defending themselves against infection faster than a half-matched transplant," Dr. Touzot said. "These results suggest that for patients without a fully matched stem cell donor, gene therapy is the next-best approach."

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The above story is based on materials provided by American Society of Hematology. Note: Materials may be edited for content and length.

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Gene therapy superior to half-matched transplant for 'bubble boy disease'

Research first to compare alternative approaches to fully matched transplant for rare immune disorder

(WASHINGTON - April 13, 2015) - New research published online today in Blood, the Journal of the American Society of Hematology (ASH), reports that children with "bubble boy disease" who undergo gene therapy have fewer infections and hospitalizations than those receiving stem cells from a partially matched donor. The research is the first to compare outcomes among children with the rare immune disorder - also known as X-linked severe combined immunodeficiency (SCID-X1) - receiving the two therapeutic approaches.

Children with SCID-X1 are born with a genetic defect that prevents them from developing a normal immune system. Because they are prone to life-threatening infections, infants with SCID-X1 must be kept in a sterile, protective bubble and require extensive treatment for survival beyond infancy. Infants with SCID are most likely to survive if they receive a stem cell transplant from a fully matched donor - typically a sibling - a procedure that replaces an infant's diseased stem cells with healthy donor cells. Following a successful fully matched transplant, infants with SCID-X1 are able to produce their own immune cells for the first time.

In the absence of a fully matched stem cell donor, infants with SCID-X1 may receive a transplant from a partial, or "half-matched," donor - typically their mother or father. They may also undergo gene therapy, a much different approach. Gene therapy for SCID-X1 involves extracting an infant's own bone marrow, using a virus to replace faulty genetic material with a correct copy, and then giving "corrected" bone marrow back to the patient. Half-matched stem cell transplant and gene therapy represent secondary treatment approaches for infants with SCID-X1. Until recently, researchers had not yet compared outcomes among children treated with each respective approach.

"Over the last decade, gene therapy has emerged as a viable alternative to a partial matched stem cell transplant for infants with SCID-X1," said lead study author Fabien Touzot, MD, PhD, of Necker Children's Hospital in Paris. "To ensure that we are providing the best alternative therapy possible, we wanted to compare outcomes among infants treated with gene therapy and infants receiving partial matched transplants."

Dr. Touzot and colleagues studied the medical records of 27 children who received either partial-matched transplant (13) or gene therapy (14) for SCID-X1 at Necker Children's Hospital between 1999 and 2013. The children receiving half-matched transplants and the children receiving gene therapy had been followed for a median of six and 12 years, respectively.

The researchers compared immune, or T-cell, development among patients and also compared key clinical outcomes such as infections and hospitalization. Investigators observed that the 14 children in the gene therapy group developed healthy immune cells faster than the 13 children in the half-matched transplant group. In fact, in the first six months after therapy, T cell counts had reached normal values for age in more than three-fourths (78%) of the gene therapy patients, compared to roughly one-fourth (26%) of the transplant group. The more rapid growth of the immune system in gene therapy patients was also associated with faster resolution of some opportunistic infections (11 months in gene therapy group vs. 25.5 months in half-matched transplant group). These patients also had fewer infection-related hospitalizations (3 in gene therapy group vs. 15 in half-matched transplant group).

"Our analysis suggests that gene therapy can put these incredibly sick children on the road to defending themselves against infection faster than a half-matched transplant," Dr. Touzot said. "These results suggest that for patients without a fully matched stem cell donor, gene therapy is the next-best approach."

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Blood, the most cited peer-reviewed publication in the field of hematology, is available weekly in print and online. Blood is the official journal of the American Society of Hematology (ASH), the world's largest professional society concerned with the causes and treatment of blood disorders.

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Study: Gene therapy superior to half-matched transplant for 'bubble boy disease'