Stem Cells to Heart Valves 5 Years Away

Harvard University, September 11, 2007

Using a type of stem cell that normally gives rise to the inner lining of blood vessels, scientists at Harvard-affiliated Boston Children’s Hospital, were able to grow heart valves. In order to stimulate the cells to grow into the proper tissue type, a mix of proteins and growth factors were used. The cells were given the appropriate shape by using a biodegradable scaffold.

The work builds on research conducted over the past decade by Professor of Surgery John Mayer explained instructor in Medicine Virna Sales, a researcher in Boston Children’s Department of Cardiac Surgery. The tissue of laboratory animals was used to conduct the experiments.

The senior investigator position for the study was also occupied by Mayer who is also in Boston Children’s Department of Cardiac Surgery. Currently, 25,000 to 30,000 children are born each year with heart defects, his research over the past 10 years has focused on helping these children.

Artificial materials and tissue from pigs are the current choice to make prosthetics out of according to Sales. The fact that they do not grow along with the human body as time goes by is a huge problem associated with using these types of prosthetics to correct defects. Additional surgeries are often the norm for children. The valve is usually replaced depending on the age of the child when surgery is performed and the type of defect present.

Researchers hope to be able to make valves out of a child's own tissue. This would be accomplished by taking a sample of the child's blood and extracting the endothelial progenitor cells or blood-vessel stem cells, and growing the valve from these cells. The child would be spared additional surgery with this method because the valves would be able to grow since they would be made from living tissue.

Sales said the procedure is still about five to ten years away from being ready for human use. The research has been published in the journal Circulation.

Two major types of stem cells can be found in the body. Giving rise to different cells within a particular tissue type, adult stem cells are one such type. For example, blood stem cells can be found in bone marrow. The constantly replace cells in the bloodstream as needed and are constantly differentiating and growing. the other type of stem cell is the more controversial embryonic variety. These cells are found in the earliest stages of life.

Prior research has sought both the right cells to start with and the proper mix of proteins and growth factors to coax the cells to differentiate into the right kind of tissue.

The type of tissue required is determined by these proteins and growth factors which signal the stem cells to grow divide and change.

The challenge presented is significant. The delicate balance of timing, dosage, and mix of factors, is straightforward in nature but no easy task in the lab.

Researchers can expose the tissues to different factors at different times my using multiple coatings on the scaffold while they learn to adjust the delicate balance said Sales. Customizing a heart valve perfectly for an individual may be possible.

Researchers will continue to refine the technology now that success has been achieved in animal models. A device designed to mimic the never-ending motion of the heart, called a bioreactor, is being used to test the properties of the engineered valves. More natural methods of growth are also being investigated. Different mixes of proteins and growth factors are being tested to see if the support scaffold can be eliminated.

“I’m going back to the basics,” Sales said, “[We’re] going to mimic mother nature.”