WHAT ABOUT MYOBLAST TRANSFER?

You may have heard about a controversial "treatment" for DMD known as myoblast transfer.

What are myoblasts, and where are they being transferred to?

Myoblasts are immature muscle cells that everyone (including boys with DMD) has. During early development, these cells fuse and become mature muscle cells (known as fibers once they're mature, because they're very long cells resulting from the fusion of the immature cells).

But nature has provided humans (and many animals) with a backup system in muscles. Even after we reach maturity, some of these myoblasts remain with us, sitting just outside the mature fibers like satellites orbiting the Earth. In fact, in this role, they're also known as satellite cells.

When muscle is damaged, these satellite cells go into action, moving in on the damaged area, quickly maturing and taking their place in the fiber. They act as a sort of patch kit.

Boys with DMD have plenty of myoblasts, and their damaged muscles get repaired like anyone else's. Unfortunately, the patch kit carries its own defect -- the lack of a functional dystrophin gene -- that plagues the mature fiber. So the repair is a temporary fix at best and, ultimately, degeneration outstrips regeneration.

In the late 1980s, just after the discovery of the dystrophin gene and protein, doctors and researchers reasoned that putting myoblasts with a functional dystrophin gene into boys with Duchenne might be a very good way to keep muscles healthy. This is where the term transfer comes from in myoblast transfer; myoblasts were transferred from healthy donors into boys with DMD.

Doctors knew even at that time that the barriers would be formidable -- that muscle covers a huge amount of territory, much of which is very hard to reach; that the immune system normally rejects any cells from outside the body; and that the new cells might not live very long in the body after going through complicated laboratory manipulations.

Nevertheless, after studies in mice looked promising, MDA-sponsored researchers began putting myoblasts into boys with Duchenne on an experimental basis in the early 1990s. Between 1990 and 1995, MDA sponsored five clinical trials of myoblast transfer in DMD.

None of these trials showed any benefit for the procedure, although some myoblasts survived the transfer (really a kind of organ transplant procedure) and produced some dystrophin. Some studies suggest the immune system is interfering with the survival of the transplanted cells. At this time, MDA is still studying myoblast transfer in animals.

MDA doesn't make specific recommendations about treatment of DMD, preferring to leave those decisions to families and their MDA clinic doctors. However, MDA's Scientific and Medical Advisory committees do make decisions about what grants to fund and which medical treatments are likely to have promise.

The Medical Advisory Committee has declined to approve grants for any further clinical trials of myoblast transfer until animal studies show that the effectiveness of the procedure can be substantially improved.

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