The answer is that they are both in the very early stages of investigation, and a lot more work has to be done before they become widely available.
Gene TherapyGene therapy is still being studied in animals and has not yet been applied to humans. The idea behind gene therapy for heart failure is to insert, into damaged heart cells, genes that "code" for certain proteins that seem likely to help the heart muscle to function more efficiently. These genes are delivered to the damaged heart through direct injection, or by infusion within the coronary arteries.
In animal experiments, several genes have been tried, including genes for sarcoplasmic reticulum (a membrane within muscle cells that helps to control calcium movement); for adrenaline receptors (receptors on cell membranes that allow cells to respond to adrenaline); and for adenylyl cyclase (a protein that helps to generate energy within cells).
While the animal testing of gene therapy has shown significant promise, it has not yet become advanced enough to proceed to clinical trials.
Stem Cell TherapyAnimal studies have used stem cells ("early" cells that are capable of transforming into many different kinds of tissue) from animal fetuses, bone marrow, and other sources. The stem cells are "transplanted" by infusing them into the coronary arteries, or by directly injecting them into the damaged heart muscle. These animal studies have shown that stem cells that are transplanted into heart muscle can survive for at least many months, and can sometimes differentiate into functioning heart cells.
Based on such promising findings, early stem cell therapy has now been applied, in a few small studies, in carefully selected patients.
Early human studies suggest that the transplanted stem cells do not actually take over the work of the heart, but rather, they produce certain substances (including cytokines, growth factors, and others) that help the "native" heart cells to function more efficiently. They also appear to stimulate "native" stem cells already present in the heart to differentiate into functioning cardiac cells.
There has been only a very limited experience so far using stem cells in patients with heart failure. The small studies that have been done suggest that stem cells can modestly improve cardiac function in certain patients with dilated cardiomyopathy. This improvement is shown by an improvement in the ejection fraction.
Potential risks of stem cell therapy include the possibility of ventricular tachycardia, which apparently is seen in many patients after the injection of stem cells. Because of this problem, some investigators now require patients to receive implantable defibrillators prior to certain types of stem cell therapy for heart failure. Also, observations suggest that in patients who have stents for coronary artery disease, restenosis (blockage) may be more frequent after stem cell treatment.
In summary, stem cell therapy for heart failure is still in its early stages of investigation. Major questions remain regarding what types of cells are best to use, how they should be delivered, how likely it is that there will be a significant long-term benefit, and whether the long-term safety of the technique is acceptable. While stem cell therapy has shown promise, investigators are still quite a ways from being ready for a major clinical trial, let alone for routine usage.
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de Muinck ED, Thompson C, Simons M. Progress and prospects: cell based regenerative therapy for cardiovascular disease. Gene Ther 2006; 13:659.