Many of the problems and hopes associated with gene therapy are exemplified in preclinical studies of genetically altered muscle cells (skeletal, cardiac, and smooth). Smooth-muscle cells of the arterial wall are being genetically engineered to synthesize growth inhibitors that might prevent restenosis after balloon angioplasty. In animal models, the injection into cardiac muscle of genes that induce new vessel formation may lead to increased blood flow. Perhaps most surprising is the finding that skeletal-muscle cells can be used as recombinant-protein factories that produce and secrete proteins that can act either locally in muscle or distally.

A number of approaches involving . . .