Gene therapy marked another successful milestone last week when it was used to completely cure eight of 10 children who had potentially fatal “bubble boy disease,” according to a study that followed their progress for an average of four years after treatment. Formally known as severe combined immunodeficiency, or SCID, the genetic disease causes its carriers to develop non-functional immune systems, typically resulting in death from infection within the first year of life without advanced treatment.
The patients in the study suffered from the second most common form of SCID, arising from a single malfunctioning gene that results in a defective enzyme, adenosine deaminase (ADA). To cure the patients, a sample of marrow cells was removed from their bodies, a virus was used to “upgrade” the cells with working copies of the gene, and then the cells were injected back into the patients’ bodies. After taking residence in the body these enhanced marrow cells were able to proliferate within the patients and supplant the original malfunctioning immune system with a functioning one.
SCID acquired the name “bubble boy disease” as a result of the famous story of David Vetter, a boy in the 70’s who literally lived in a sterilized vessel, or bubble, for 12 years in an effort to protect him from infectious encounters. Vetter eventually died in 1984 when an attempt to cure him with a bone marrow transplant failed. This disease, diagnosed in roughly 40-100 children in the United States each year, is particularly heart wrenching because it necessarily afflicts children.
Although the success of gene therapy against SCID is just now being formally announced, the therapy is actually the culmination of a fabled medical journey that has covered almost 20 years…
In 1990 SCID gained the notoriety of being the first disease ever attempted to be treated with gene therapy when it was used to treat a 4 year old girl with the ADA form of SCID. The girl survived and showed marked improvement, but there was debate as to whether the gene therapy or several other concurrently used medications and therapies were responsible.
In response, several similar trials were launched across the world in the late nineties against the most common form of SCID, known as X-SCID. These trials were brought to an abrupt halt years later when sadly it was revealed that the therapy had a high probability of inducing leukemia in its patients. The news was a devastating blow to the emerging field of gene therapy, dashing the high hopes of many for the therapy and giving the field a bad name.
Although gene therapy was halted in trials involving X-SCID, trials continued for several other blood related diseases, retinal diseases, and even the second most common form of SCID involving ADA, known as ADA-SCID. It is success with ADA-SCID that is being announced today.
Although gene therapy now seems vindicated today as a valid treatment for ADA-SCID, it should be noted that gene therapy is not the only medical treatment available for ADA-SCID sufferers. Bone marrow transplants from a compatible donor have successfully cured many ADA-SCID patients over the years. Bone marrow transplants are similar to gene therapy in that the goal is to replace the patient’s malfunctioning immune system with a new, functioning one. Unfortunately, finding a compatible bone marrow donor can require time that the patient cannot afford and the transplant does not always work. Twice weekly shots of the ADA enzyme, along with heavy use of antibiotics and antibody infusions, can also help, but this treatment is expensive, error prone, and does not fully protect patients.
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