Currently, there is no effective treatment to restore or improve vision in patients suffering from blindness (retinal degeneration, RD) due to such diseases as age-related macular degeneration and retinitis pigmentosa. Alleviation of these diseases requires both new photoreceptors (the light-sensing cells in the back of the eye) and retinal pigment epithelium (RPE), which supports the photoreceptors. Proof of concept has been demonstrated by improved vision resulting from transplantation of fetal retinal progenitor sheets together with supporting RPE in both animals and patients with retinal disease. The ultimate goal of our research is to alleviate blindness using a renewable source of stem-cell derived retinal sheets.
Human embryonic stem cells (hESCs) are developed into sheets of immature retinal tissue that contains progenitors of photoreceptor as well as RPE cells. Optimization of this differentiation protocol will create an unlimited supply of immature retinal tissue that can be transplanted into the eyes of people with advanced blindness. hESCs and induced pluripotent stem cells (iPSCs) can be coaxed to “self-assemble” into early stages of eye development and develop into layers of cells that resemble the normal retina. The hypothesis of this research is that hESCs can be consistently differentiated into sheets of immature retinal tissue which can restore visual responses in a rat model of retinal degeneration. This particular model is immunodeficient and therefore does not reject human cells. In the third year of our research program, we will increase the production of effective retinal sheets in a way that complies with good manufacturing practice as outlined by the US Food and Drug Administration. This research program will ultimately help to restore vision in patients suffering from retinal diseases.
In year 2 of this 3-year grant, the procedures to obtain 3D retina from hESCs have been improved. The development of retinal structures in cell culture must follow closely its development within a living organism. These cellular products have been shown to express appropriate retinal markers using labeling methods called immunohistochemistry and quantitative polymerase chain reaction (qPCR) which determines which and how many genes are expressed. 3D- retinal progenitor sheets derived from hESCs and human fetal retina have been transplanted into the eyes of rats with fast retinal degeneration, which have been engineered not to reject human cells. In this 2nd year of the grant, such transplanted RD rats have been tested for visual acuity (how they can discriminate moving stripes) and electrical responses to light in the brain (superior colliculus recordings) after survival times of 4 – 8 months after transplant. Preliminary data indicate visual improvements after transplantation by both measures. In the 3rd year of the grant we will also use a second, newly developed rat model of retinal degeneration, immunodeficient RCS rats with a slower rate of retinal degeneration that may result in a higher degree of visual restoration.
This work will be presented at several meetings this year (ARVO, ICER, Neuroscience). One manuscript has been submitted, and several manuscripts are in preparation. The laboratory has attracted many students who are interested to learn about retinal development and vision restoration. The work has also led to new collaborations.