Gene Therapy Under Pressure
Researchers at Brigham and Women's Hospital (Boston), Harvard Medical School (Boston), and Stanford University (Stanford, CA) have developed a highly efficient, pressure-mediated technique for introducing oligodeoxynucleotides into cardiovascular tissues. As reported in the May 24 issue of PNAS, Victor Dzau and collaborators showed that they could achieve ex vivo oligo uptake into human veins and rat myocardium without damaging or stretching the tissue using a special device that equalizes the pressure inside and outside the tissue during transfection. In addition, by using antisense oligos, they demonstrated specific transcriptional blocks in transfected tissue. This system may offer a safe alternative to the use of viral vectors, chemicals, and other potentially toxic agents for the genetic manipulation of tissue used in cardiovascular transplants and grafts.
Work in Dzau's laboratory has focused on developing gene therapy strategies for cardiovascular proliferative diseases such as vein graft atherosclerosis, a common condition leading to the failure of as many as 50% of cardiac and leg bypass surgeries. This is thought to be the result of putting veins, the usual source of bypass material, into positions normally taken by arteries. The elevated pressures endured by arteries stimulates neointimal hyperplasia, or growth of the cells lining the grafted vein, which in turn renders the vessel especially susceptible to the formation of atherosclerotic plaques.
Wanting to improve the efficiency and safety of transfection protocols, these researchers tested the effects of introducing pressure while bathing the tissue in an oligonucleotide-containing solution. At optimum pressure, a large proportion of the nuclei of the treated tissue showed uptake of FITC-labeled oligos—90% of cells in human saphenous vein (the large leg vein commonly used in bypass surgeries) segments and 60% of rat myocardium cells. Although the mechanism for this phenomenon is largely unknown, uptake of the oligos into the nucleus is an added benefit, since not only does it put the oligos close to its target, but it avoids possible degradation in lysozomes.
The researchers further demonstrated that with antisense oligos, they can prevent the expression of several genes that might mediate some of the bad outcomes of transplants and grafts. The expression of the cytokine IL-6, thought to play a role in arteriosclerosis, was blocked in human vein fragments transfected with antisense oligos. In addition, they achieved a reduction of intercellular adhesion molecule (ICAM-1) RNA in rat myocytes commensurate with the amount of oligo update. ICAM expression is elevated in cardiac myocytes following transplantation, and may be involved in the host immune response to the tissue.
This system joins the arsenal of tools for gene therapy and manipulation, without some of the drawbacks and concerns of some of the others currently in use. In addition to providing a safe and efficient gene delivery system for cardiovascular tissue, it could prove useful in other oligo and antisense strategies.
For more information: Victor Dzau, Professor and Chief, Center for Cardiovascular Research, Brigham and Women's Hospital/Harvard Medical School, 75 Francis Street, Boston, MA 02115. Tel: 617-732-6340. Fax: 617-732-6439. Email: vjd@bics.bwh.harvard.edu.
By Laura DeFrancesco