Although stem cells were discovered in the mid-1800s and the subject of experimentation in the early 1900s, it’s only been in recent decades that they’ve truly caught the imagination of medical researchers and the public. Today, our understanding of these cells is expanding dramatically, and research has proliferated as their potential has become clear. Nevertheless, stem cell research is still in its infancy. Because a host of basic questions remain unanswered, research around the world is moving in multiple directions, testing many different possible ways to derive stem cells and apply them in vitro for research and in vivo for treating or preventing disease.
A stem cell is defined as an undifferentiated cell that has the potential to become a number of specific cell types. However, depending on the derivation of the stem cell, its fundamental characteristics may be significantly different. There are four primary stem cell types: embryonic, taken from very early fertilized embryos; parthenogenetic, taken from unfertilized eggs with a simpler genetic sequence for researchers to manage; so-called adult stem cells, found in different organs and designed to differentiate into the cell types found in that organ only; and induced pluripotent stem cells, which are differentiated cells (for example, skin cells) that are coaxed into returning to an undifferentiated state, from which they may then evolve into any number of other cell types. Each type of stem cell has specific advantages and drawbacks that make it better suited—at least in theory—for specific applications.
As is often the case in medical research, the eye has become a popular target. That’s partly because results are typically easier to monitor in the eye than in other organs, and partly because much of the eye in immune-privileged, making it receptive to treatments that might trigger rejection in other parts of the body. Current targets include the retina, cornea, trabecular meshwork and simply stabilizing abnormal blood vessels.