Muscling in
THE ideal way of curing an inherited disorder would be to adopt gene therapy (correct the genetic defect). Failing that, it would be worth exploring whether the severity of the disorder might be ameliorated by substituting a functional gene product - protein - in place of the dysfunctional product (or no product).
One of the most novel concepts to have emerged in recent years in the area of gene therapy is the possible use of muscles as factories for the production and release of proteins. The basic idea is simple. A gene encoding the therapeutic protein of interest is incorporated into a virus, or into what is known as a vector'. The virus is then used to infect primary myoblasts - multi- nucleate muscle cells capable of prolonged division - that are isolated from the skeletal muscle tissue of the host.
These myoblasts are capable of synthesising the desired protein and are now implanted into the tissue of the patient. It is possible that the patient's own cells may not be capable ofserving the purpose, in which case the myoblasts will need to be borrowed from a healthy donor with a host-compatible immune system.
Much of the pioneering research in this area has been done by Jyotsna Dhawan, Helen Blau and colleagues at the Stanford University School of Medicine, us. The work had till recently been concentrated on mice. The only clinical application of myoblast transplantation so far has involved an attempt to treat Duchenne muscular dystrophy, a progressive disorder of muscles; the results have been disappointing. It is envisaged, however, that more systematic human trials might begin in the near future.
The uses of myoblast transplantation, include transfer to the circulation of (normally) non-muscle proteins such as growth hormones and blood coagulation factors, delivery of protein vaccines by transforming the donor muscle cells with the DNA that encodes the desired vaccine and nerve regeneration induced by the release of nerve growth factors by the injected myoblasts. Of all the uses of this therapy that have been talked about, the one that strikes the imagination most concerns the heart, where its practice could promote fresh vascularisation so as to improve blood flow and repair cardiac tissue damaged by a heart attack.
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