In the 1990s, European scientists actually cured SCID in some patients, using a technique called gene therapy. This process involves removing defective blood cells from a patient, inserting a new gene with the help of a virus and then putting the cells back into the body. Those cells then build up the patient's immune system.
At first, this treatment in the 1990s and early 2000s looked really promising.
"Of the 20 patients, they all had immune recovery," says
Donald Kohn, an immunologist at UCLA's Broad Center of Regenerative Medicine and Stem Cell Research. "But, over time, five of them went on to develop a leukemia."
He says 18 of those original patients are still alive today, but the leukemias put an understandable pall on the whole field of gene therapy.
Scientists went to work to figure out how to inject new genes into cells without triggering leukemia, a cancer of blood cells. And they think they've succeeded.
Over time, there has been gradual improvement in gene therapy. The latest advance,
reported in the New England Journal of Medicine on Wednesday, details a study of eight infants who have a type of SCID called SCID-X1.
The gene to correct the problem was inserted into a modified version of HIV, the virus that causes AIDS. That engineered virus can't cause AIDS, and it has been further tweaked to reduce the risk that it could trigger leukemia.
Gene therapy has been used successfully over the past decade. Scientists at St. Jude Children's Research Hospital in Memphis, Tenn., modified the procedure for SCID by giving the infants a short course of chemotherapy before introducing the new gene. This helped the new cells take up permanent residence. The babies developed apparently healthy immune systems, according to the new study.
