Stem cells are undifferentiated cells that are characterized by their ability to morph into a diverse range of specialized cell types. This process is called differentiation and occurs naturally numerous times during the development of an organism. Although the most dramatic differentiation occurs during the early development stages, differentiation is also common in adults. Adult stem cells divide and morph into specialized daughter cells during tissue repair and during normal cell turnover.
Experimental procedures allow the transformation of stem cells into specialized cells with characteristics consistent with cells of various tissues. However, we are far from understanding the exact conditions necessary to produce and sustain any cell type at will (there are about 210 distinct types in the adult human body). Nevertheless, as stem cells are already involved in the natural repair process of the body, it seems only logical to “coax” stem cells into repairing tissue that might not be repaired naturally. Hence, using stem cells as therapy holds great promise as a viable treatment option for various diseases in the future, including heart disease.
The first step is to use stem cells to restore damaged cells or even parts of tissue, but futuristic visions include the development of biological substitutes of entire organs. Already today, researchers are able to fabricate certain tissues in the laboratory. Unfortunately, most natural tissues are far beyond the functionality and biomechanical stability that is possible from laboratory-grown tissues.
Human embryonic stem cell colony on an embryonic fibroblast feeder layer.
Growing tissue or whole organs is very complex with many aspects still unknown. Chemical components and physical parameters have to be maintained within a very tight range in order for the tissue to develop correctly. For example, it is known that artificial tissue of endothelial cells, the cells that line the interior surface of blood vessels, need a constant flow of fluid to exhibit growth characteristics resembling blood vessels. But many other crucial factors remain unidentified. Hence, laboratory-grown tissues destined for transplantation and the development of true human replacement parts remains for now in the realm of science fiction.