Scientists at the University of Wisconsin-Madison announced today that they have succeeded in generating retinal cells from stem cells. The retina is the light-sensitive portion of the eye that is responsible for seeing. Many types of blindness are caused by the cells in the retina not functioning properly. For example, in the disease wet macular degeneration, blood vessels start growing over the retina and induce death of the neurons that transmit light. Another conditions causing retinal damage include diabetic retinopathy and long term glaucoma. While treatmetns exist that slow down progression of conditions that cause retinal damage, to date, no treatments exist that reverse damage once it has occurred.
Dr. David Gamm was the head of the research group that successfully created retinal cells outside of the body, is a member of the Ophthalmology and Visual Sciences Department, and of the UW Eye Research Institute. He used a new type of stem cell called inducible pluripotent stem cells (iPS) as the starting material for the experiments. These iPS cells are stem cells created from the skin. By introducing certain pieces of DNA into skin cells, the cells literally “become younger” and take the characteristics of stem cells. These “artificial” stem cells have been previously used for generating a variety of tissues in the test tube and even in some animal experiments. For example, iPS cells have been previously made into pancreatic islets that produce insulin (Zhang et al. Highly efficient differentiation of human ES cells and iPS cells into mature pancreatic insulin-producing cells. Cell Res. 2009 Apr;19(4):429-38) and could one day be used in the treatment of diabetes. The advantage of iPS cells is that they can be made from the same individual for which they will be used. In other words people are able to use their own cells as stem cells.
Unfortunately, the disadvantage of iPS cells is that they are very similar to embryonic stem cells. While obviously they do not have the ethical concerns associated with embryonic stem cells, since they come from the skin, iPS cells cause cancer. There is a specific type of cancer, called a teratoma, that forms when embryonic stem cells or iPS cells are injected into animals. One of the reasons for this type of cancer is because the cells are very primitive and do not know how to interact with the body around them. To date there as been one approval by the FDA for an embryonic stem cell based clinical trial by the Menlo Park company Geron Inc, but that approval was withdrawn due to concerns about some of the animal safety data without any patients being treated.
For generating treatments based on either iPS or embryonic stem cells, it will be essential to make sure that the cells are made to mature in the test tube before implantation into humans. To date, this has been one of the major stumbling blocks.
The discovery of making retina from iPS cells is, however, a major finding. One reason is that by being able to make retina cells in large quantities, the possibility of using these cells to screen for drugs that may protect them from damage or death emerges.
Retinal-like cells have been previously made from other stem cells, including from bone marrow (Wang et al. Transplantation of quantum dot-labelled bone marrow-derived stem cells into the vitreous of mice with laser-induced retinal injury: Survival, integration and differentiation. Vision Res. 2009 Sep 25) and cord blood (Koike-Kiriyama et al. Human cord blood cells can differentiate into retinal nerve cells. Acta Neurobiol Exp (Wars). 2007;67(4):359-65) stem cells, which do not have the problems of cancer formation associated with embryonic or iPS cells.