Gene Therapy Beats Half-Matched Stem Cell Transplant in Side-by-Side Comparison to Treat ‘Bubble Baby’ Disease

If you are born with Severe Combined Immunodeficiency (SCID), your childhood is anything but normal. You don’t get to play with other kids, or be held by your parents. You can’t even breathe the same air. And, without treatment, you probably won’t live past your first year.

The bubble boy.  Born in 1971 with SCID, David Vetter lived in a sterile bubble to avoid outside germs that could kill him. He died in 1984 at 12 due to complications from a bone marrow transplant. [Credit: Baylor College of Medicine Archives]

The bubble boy. Born in 1971 with SCID, David Vetter lived in a sterile bubble to avoid outside germs that could kill him. He died in 1984 at 12 due to complications from a bone marrow transplant. [Credit: Baylor College of Medicine Archives]

This is the reality of SCID, also called “Bubble Baby” disease, a term coined in the 1970s when the only way to manage the disease was isolating the child in a super clean environment to avoid exposure to germs. The only way to treat the disorder was with a fully matched stem cell transplant from a bone marrow donor, ideally from a sibling. But as you may have guessed, finding a match is extraordinarily rare. Until recently, the next best option was a ‘half-match’ transplant—usually from a parent. But now, scientists are exploring a third, potentially advantageous option: gene therapy. Late last year, we wrote about a promising clinical trial from UCLA researcher (and CIRM Grantee) Donald Kohn, whose team effectively ‘cured’ SCID in 18 children with the help of gene therapy. Experts still consider a fully matched stem cell transplant to be the gold standard of treatment for SCID. But are the second-tier contenders—gene therapy and half-matched transplant—both equally as effective? Until recently, no one had direct comparison. That all changes today, as scientists at the Necker Children’s Hospital in Paris compare in the journal Blood, for the first time, half-matched transplants and gene therapy—to see which approach comes out on top. The study’s lead author, Fabien Touzot, explained the importance of comparing these two methods:

“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.”

So the team monitored a group of 14 SCID children who had been treated with gene therapy, and compared them to another group of 13 who had received the half-matched transplant. And the differences were staggering. Children in the gene therapy group showed an immune system vastly improved compared to the half-matched transplant group. In fact, in the six months following treatment, T-cell counts (an indicator of overall immune system health) rose to almost normal levels in more than 75% of the gene therapy patients. In the transplant group, that number was just over 25%. The gene therapy patients also showed better resilience against infections and had far fewer infection-related hospitalizations—all indictors that gene therapy may in fact be superior to a half-matched transplant. This is encouraging news say researchers. Finding a fully matched stem cell donor is incredibly rare. Gene therapy could then give countless families of SCID patients hope that their children could lead comparatively normal, healthy lives. “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,” explained Touzot. “These results suggest that for patients without a fully matched stem cell donor, gene therapy is the next-best approach.” Hear more about how gene therapy could revolutionize treatment strategies for SCID in our recent interview with Donald Kohn:

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