Currently, there is no effective treatment to improve vision in patients suffering from blindness (retinal degeneration, RD) due to diseases such 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 in patients 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 improve visual responses in rat models of retinal degeneration. These particular rats are immunodeficient and therefore do not reject human cells. In the third year of our research program, we have increased 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 improve vision in patients suffering from retinal diseases.
In the last year of this 3-year grant, the procedures to obtain 3D retina from hESCs have been optimized. 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- retina organoid sheets derived from hESCs have been transplanted into the eyes of two different rat RD models which have been engineered not to reject human cells. For the first rat model with fast RD, we have completed the experiments demonstrating that these rats exhibit improved visual acuity (this means how they can discriminate moving stripes) and electrical responses to light in the brain (superior colliculus recordings) 4–8 months after transplantation of retina organoids. Data also show that transplants develop photoreceptors and other retinal cells, integrate with the host retina, and make synaptic connections with the host retina. These experiments are being repeated in a second rat model of RD – immunodeficient RCS rats with a slower rate of RD. Preliminary results are encouraging. These experiments are still ongoing.
This work has been presented at several meetings last year (ARVO and Neuroscience), and at the NEI retina organoid challenge meeting. One paper has been published, 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.