A stem cell breakthrough could lead to a treatment for muscular dystrophy (MD), research has revealed.
Stem cell treatment dramatically improved some dogs' symptoms
An Italian-French team found transplanting stem cells into dogs with a version of the disease markedly improved their symptoms.
Writing in the journal Nature, the team said the work paved the way for future trials in humans.
Scientists said it was a major step forward and bolstered the idea that stem cells could be used to treat MD.
Muscular dystrophy is a group of genetic disorders that cause the muscles in the body to gradually weaken over time and mobility to be lost. It shortens life span and there is currently no cure.
The researchers, led by a team at San Raffaele Scientific Institute, in Milan, Italy, looked at the most common form of the disease, Duchenne muscular dystrophy.
This condition, which usually only affects boys, appears in about one in every 3,500 male births and is caused by mutations in a particular gene that lead to a lack of dystrophin, a protein involved in maintaining the integrity of muscle.
The team had previously seen promising results when they injected stem cells into mice with a version of this disease, but turned to dogs for their next trial because they replicate the muscle-wasting disease more accurately.
The researchers used a form of stem cells, gathered from blood vessels, called mesoangioblasts, which are "programmed" to turn into muscle cells.
They isolated the stem cells from both healthy dogs and also from MD dogs, with the latter's stem cells then being modified to "correct" the mutated gene.
The scientists proceeded to inject these different types of stem cells into dogs with MD.
They found that transferring the stem cells five times at monthly intervals produced the best results.
Overall, injections of stem cells taken from healthy dogs showed the most improvement.
Four out of the six dogs who received these stem cells saw the return of dystrophin and regained muscle strength. One dog that was injected at an early-stage of the disease retained the ability to walk, and two dogs injected at a late-stage of the disease had their mobility returned. Of the remaining two, one died early and the other, the scientists believe, did not receive enough cells.
The experiment to inject MD dogs with their own "corrected" stem cells proved less successful, although the dytrophin protein returned.
This approach was investigated because, should stem cell treatment move into humans, it would mean patients could be injected with their own cells, minimising the chances of rejection and avoiding the need to take immunosuppressant drugs.
The researchers wrote: "The work reported here sets the logical premise for the start of clinical experimentation that may lead to an efficacious therapy for Duchenne muscular dystrophy."
Dr Marita Pohlschmidt, director of research at the Muscular Dystrophy Campaign, UK, said: "We feel encouraged by the work because the results provide initial evidence that we might be one step closer to a stem cell treatment for Duchenne muscular dystrophy."
Dr Stephen Minger, a stem cell researcher at Kings College London, said: "This is an excellent piece of work demonstrating significant functional improvement in a naturally occurring disease in dogs that is very similar to that in humans.
"Although it will likely to be some time before this work can move to humans, it is nevertheless an important study in developing therapies for muscular dystrophies."
Professor Dominic Wells, of the gene targeting group at Imperial College, London, said: "This is yet another example of the vital contribution animal research makes to the development of treatments for human disease.
"This is the first piece of research that has convinced me that stem cell therapy could play a role in treatment for Duchenne muscular dystrophy."
Kay Davies of the MRC Functional Genetics Unit, University of Oxford, said: "The use of stem cells to treat human disease holds great promise, but the actual delivery of such therapy is thought to be many years away."
The data, she said, changed this view. However, she added that the researchers needed to find out why not all dogs responded positively.