The 2012 Nobel Prize for medicine was awarded this month to two scientists who discovered how certain mature adult cells could be converted to stem cells. The announcement of the award was accompanied by the statement that this technology was about to be tested in humans for the treatment of macular degeneration. As a result, I thought it appropriate to devote this blog to an update on the use of stem cells for the treatment of retinal diseases.
Stem cells are cells that differentiate and develop to become a wide variety of cells in the body. Conceptually one could imagine replacing damaged cells with stem cells that in turn could develop into the cells that have been damaged and would produce tissue that is free from this damage.
There are two major types of stem cells: those derived from embryos, called Embryonic Stem Cells (ESC’s) and those derived from special adult cells, called somatic stem cells, or induced pluripotent stem cells, IPSC’s.
Various kinds of ESC’s have been implanted in and around the retina in both animals and humans. Cell growth and differentiation into retinal cells has been demonstrated and limited improvement in vision has been observed.
In February of this year a group of scientists reported in the medical journal, “The Lancet,” that two patients had been successfully treated with ESC’s. One of the treated patients had Stargardt’s disease, a form of macular degeneration that occurs in younger people; the other had Dry Age-related Macular Degeneration. Both patients showed small gains in vision and neither exhibited any significant side effects as a result of over-proliferation of the implanted cells. This study, being conducted by a Massachusetts-based biotechnology company, Advanced Cell Technology, is designed primarily to determine the safety of ESC implantation, but does give hope that this technology will be used safely to restore vision in the not-too-distant future. Other companies, such as Pfizer Inc., are also planning trials of ESC’s in macular degeneration.
IPSC’s provide the obvious ethical benefit in that they do not require the use of human embryos. In addition, there is reason to believe that the IPSC’s will have less potential for allergic reactions, since they will be derived from the patient’s own skin.
IPSC’s have shown promise in many animal studies, including one conducted in Toronto by a group headed by Dr. Derek van der Kooy, professor of molecular genetics at the University of Toronto. Dr. van der Kooy’s group used IPSC’s derived from human retinal stem cells, which they developed into photoreceptor cells and, in turn, implanted them into mice. The implanted cells grew successfully in the mice retinas.
Nobel Prize winner Dr Shinya Yamanaka announced that scientists at the Riken Center for Developmental Biology in Kobe, Japan, plan to use IPSC’s derived from skin in a trial among patients with macular degeneration. This would be the first human trial with IPSC’s.
The studies I have discussed are those that have progressed the furthest, but there are many laboratories working in this area and it seems highly likely that other developments will emerge soon. Unfortunately, the very nature of stem cells will require long-term study to ensure that they do not develop into any undesirable cells or produce any negative side effects. These are exciting times for this technology but it may be a while before it is generally available to patients.