However, this mechanism is relatively inefficient in the brain. Transplanted bone marrow cells have a hard time getting across the blood-brain barrier, and not much enzyme was delivered to brain cells by this treatment. So why was the treatment working for the Twitcher mice?
"We went back to the drawing board and asked what are each of these approaches doing?" Sands says.
The researchers could see that gene therapy was getting functional genes to brain cells, but they began to suspect that bone marrow transplantation was working in an entirely different way -- it was reducing inflammation in the brain by a mechanism that hasn't yet been clearly defined.
"We hypothesized that if we could supply high levels of enzyme to the brain with gene therapy and at the same time decrease inflammation in the brain with bone marrow transplantation, we might have an effect," Sands says. "However, we never imagined that the two approaches would synergize to the degree we saw."
Inflammation in the brain in Krabb disorder is an important factor in neural damage. Sands believes reducing inflammation allowed the gene therapy to be much more effective in the brain, even in areas far from the injection site that received low doses of the gene.
"Nothing we used here hasn't already been used for other disorders," Sands says. "We are going to work on optimizing the therapy in the lab, and I think the combination approach could potentially be in the clinic in a few years."