The recombinant virus particles used as gene transfer vectors do not have the ability to replicate. Table 1 lists gene therapy vectors. Recombinant adenoviruses are commonly used viral vectors and unfortunately achieve gene expression for only a few weeks after infection. The ventricular myocardium appears to be receptive to the introduction of foreign genes, and gene transfer has been achieved using direct injection into the myocardium or intracoronary infusion of material that has been genetically engineered in cell culture.
Small, circular DNA pieces called plasmids are simple tools of molecular biology. They lack viral elements that substantially reduce the risk of toxicity and immune reactions. Plasmids are taken up by most cells, however, and promote low gene transfer effects. They are also unprotected against cellular defense mechanisms. Never¬theless they appear to be safe, although their effects appear to be transient.
There is ongoing development of an artificial virus that may incorporate the plasmid necessary to confer effective translocation into the cell at high efficiency. Third genera¬tion lentiviruses are also being tested.

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