The combination of an artificial chromosome and a specialised kind of stem cell has enabled scientists to reverse muscle wasting in mice with muscular dystrophy.
This degenerative disease occurs when a person inherits a faulty copy of a large gene called dystrophin, which is carried by the X chromosome. Defective dystrophin causes muscle cells to progressively break down, leading to weakness and disability. But the enormous size of the dystrophin gene - it's the longest gene we carry - precludes the use of viruses as vectors to carry healthy copies of the genes into affected cells.
Instead, writing in Science Translational Medicine, Giulio Cossu and his colleagues have found a cunning alternative. Having previously shown that a population of stem cells known as mesoangioblasts, which are normally harboured within the walls of arteries, can migrate out of blood vessels and turn into new muscle cells, the researchers have successfully turned the cells into the cytological equivalent of a Trojan Horse.
The team have built a human artificial chromosome (HAC) containing a healthy copy of the dystrophin gene, which they then added to a population of mesoangioblasts grown in cell culture. Then, working with mice with the rodent equivalent of muscular dystrophy, they reinfused the cells into the animals' bloodstreams. From there they found that they entered the diseased muscle, fusing with the existing cells to produce new, healthy muscle tissue.
Compared with control animals, the treated mice had 80% better muscle function in a test of endurance and fourfold more voluntary motor activity. A patient's own mesoangioblasts could be used in the same way, say the scientists, to enact genetically-compatible therapies for the disease in affected humans. And because the cells would be the patient's own, immune-suppressing drugs would not be required to prevent the body from rejecting the therapeutic tissue.