Approximately 1.1 million Americans are legally blind. A form of retinal degeneration called age-related macular degeneration (or AMD) is the most common form of blindness in older Americans, affecting almost 1 in 3 individuals older than age 75. The macula is the critical portion of the retina that is required for central vision and for seeing color and fine detail. The retina is the tissue at the back of the eye that senses light and conducts visual signals to the brain. Other forms of retinal degeneration, such as retinitis pigmentosa, may affect other areas of the retina or even the entire retina. These conditions are inherited and affect individuals in their earlier years, limiting their lives at a time when they could be most productive. No cures are currently available for patients with any of these blinding eye diseases. The long-term goal of our proposed experiments is to develop therapies for these patients using human embryonic stem cells (hESC). These cells have the unusual ability to develop into any cell type in the body, a characteristic that suggests they may have the potential to restore lost or damaged tissue anywhere in the body. Researchers have previously shown that hESC can be cultivated into cells with the characteristics of developing retinal cells (retinal progenitor cells). However, these cells have not yet been tested for their ability to treat retinal degeneration. We believe that properly modified retinal progenitor cells derived from hESC could be used to preserve or even replace damaged retinal tissue. Our laboratory also does research on a tumor of the retina, retinoblastoma, which arises from retinal progenitor cells. Current evidence indicates that if these cells can be modified to curb their growth, they may also serve as useful source of tissue for restorative therapy in patients with retinal degenerations. We propose to investigate these potential cell-based therapies by: 1. Creating hESC-derived retinal progenitor cells and genetically engineered retinoblastoma cells with the potential to preserve or replace damaged retina. 2. Transplanting these cells into special strains of rats with partial retinal degeneration. Analysis of retinal function in these rats will determine whether hESC can slow or prevent further retinal deterioration. 3. Transplanting these cells into rats and mice with complete retinal degeneration to determine whether these cells can regenerate functional retina and restore vision. We believe this work has low likelihood to be funded by the federal government because of the current funding climate and the fact that only limited work in this research area has been federally funded. Nonetheless, we believe the eye is an ideal organ system for testing the therapeutic potential of hESC because it is amenable to precise functional and electrophysiologic assessment of treatment response. In addition, the eye is an immune privileged site that is less likely to reject implanted tissue.
Statement of Benefit to California:
The economic costs associated with visual disability are enormous. The National Eye Institute estimates that the annual cost of visual disorders and disability in the U.S. was $67.6 billion in 2003 (http://www.nei.nih.gov/eyedata/hu_estimates.asp). These costs include direct expenses such as visits to doctors, surgery, ophthalmic drugs, hospital care and optical devices in addition to indirect costs such as days lost from work. Assuming the cost of visual disability in California is proportional to its percentage of the U.S. population, the economic burden of visual disability in California exceeds $8 billion per year. This estimate does not include the additional costs of educating children with visual impairments. According to a report commissioned by the California Department of Education, over 5,046 special education students in the public school system required vision services. The average cost of special education services for students with visual impairment was $21,745, resulting in a total cost to the state of nearly $110 million in that year. (Study of the Incidence Adjustment in the Special Education Funding Model, Exhibits 2-35 and 4-2, http://www.cde.ca.gov/fg/fr/se). The development of more effective treatments to reduce visual disability would therefore have a tremendous positive economic impact on the state as a whole. Such innovations would also greatly improve the quality of life of Californians suffering from diseases of the eye. The most frequent cause of blindness in the United States is age-related macular degeneration (AMD), a disease that affects 30% of Americans over the age of 75 (Klein R et al, Ophthalmology 99:933-943, 1992,). The incidence of this disease ranges worldwide up to 41.6% in older populations (Hirvela H et al, Ophthalmology 103:871-877, 1996). The incidence of age-related macular degeneration in California will continue to rise as the baby boom generation ages. Retinal degenerative diseases like AMD are characterized by loss of photoreceptors, the light-sensing cells of the eye. In patients with AMD, photoreceptor loss results in loss of central visual acuity. When central vision is lost, patients also lose their ability to read, to drive, to work, and to interact with the visual world. Other retinal degenerative diseases, such as retinitis pigmentosa, can be inherited and affect individuals in their earlier years, limiting their lives at a time when they could be most productive. No cures are currently available for patients with these blinding eye diseases. The long-term goal of our proposed experiments is to develop human embryonic stem cell (hESC) based therapies which can slow photoreceptor loss in patients in early- to mid-stage retinal degeneration, and possibly even replace lost photoreceptors and restore vision in patients blinded by end-stage disease. We hope that this work will lead to better understanding of retinal degeneration and potentially a cure for these debilitating diseases.
SYNOPSIS: Dr. Joan Marie O'Brien proposes to create hESC-derived retinal progenitor cells and genetically engineered retinoblastoma cells to protect or replace retina, to transplant these cells into a strain of rats that have partial retinal degeneration, and finally to transplant the cells into rats and mice with complete retinal degeneration. The partial degenerated retinas will not require replacement of photoreceptors while the rodents with complete retinal degeneration will require replacement of both photoreceptors and ganglion cells. SIGNIFICANCE AND INNOVATION: The overall goal is to use either retinoblastoma cells or hESCs as a source for new photoreceptors in the treatment of retinal degenerations. The idea of using retinoblastoma cells for deriving new photoreceptors was tried several years ago by del Cerro's group and was not very successful. The use of hESCs for the derivation of photoreceptors for transplantation is more likely to lead to an effective strategy, though the approach proposed is currently being carried out by at least three other groups. This proposal is trying something that has been shown to work with mouse ESCs. A recent study published in Nature, for example, has already shown that mouse stem cells can replace retinal ganglionic cells and retore vision to blind mice. Many laboratories are attempting to do what is being proposed in this application. On the other hand, Dr. O'Brien's work with retinoblastoma after arresting cell cycle and restoring the p53 pathway is unique and quite innovative. STRENGTHS: The PI is an experienced and productive researcher who has done very interesting work with retinoblastoma cells and now seeks to study human retinal cells produced from hESCs. Similar experiments have been carried out using mouse ESCs and it is important to try to show that the same can be achieved with hESCs. The proposal is well-written and detailed, supported with many studies. Dr. O'Brien is well supported by NIH grants. The PI has an excellent group of collaborators; the team is very experienced and includes Jacque Duncan who is a retina specialist with extensive laboratory experience doing electrophysiological tests, Matthew LaVail who is very experienced with human retinal degeneration, and Julie Schnapf who is an expert on phototransduction and works on guinea pig retina. The laboratory is strongly supported by core facilities in the Department of Opthalmology at UCSF. WEAKNESSES: The PI has little experience with hESCs and this is evident with his/her confusion about using LIF to keep the cells undifferentiated (this works for mouse ESCs but not hESCs). The methods and assesment for characterization of hESCs that have been directed to a retinal fate are not well described and do not go further than methods published by other labs. The possibility that retinoblastoma cells can be engineered to be "safe" for transplantation by introducing a wild-type RB1 gene will only work if that is the only mutation in the cells. However, most tumors develop additional mutations and extensive heterogeneity. The re-introduction of the RB1 gene may then only inhibit the proliferation of those cells that did not acquire additional growth promoting mutations (which may be a minority of the population in most tumors). Retinoblastoma cells can develop some of the gene expression characteristics of normal retinal cells, but there are many reports of cells expressing characteristics of different types of neurons/photoreceptors in a single cell. Thus, there is little evidence to support the possibility that the derivation of a functional photoreceptor from retinaoblastoma is feasible. Finally, the proposal does not address the issue of immune-rejection of hESCs and their derivatives transplanted into the rats and mice. More details are needed concerning the hESC work, including the specific stains that will be used to visualize the transplanted cells. DISCUSSION: The PI has extensive experience with retinoblastoma research; while the PI has no experience with hESC, he/she has assembled an excellent team - perhaps one of the strongest retinal degeneration groups in the country. The aim of directing hESCs to differentiate into photoreceptors is a feasible aim. The weakness is that half of the application focuses on retinablastoma cells. Nevertheless, one of the reviewers had serious reservations about this proposal because the primary interest described in the proposal is not merely in retinal replacement, but specifically in the use of retinoblastoma cells for cell replacement upon forced differentiation. A similar strategy, tried many years ago, was abandoned when it resulted in tumor formation in mice. Follwing this finding, everyone abandoned this concept. This applicant believes they can succeed where others have failed by genetic modification of RB lines. A likely problem with this approach is the likely heterogeneity of the resulting population. It would be surprising if such cells were (clinically) useful. The reviewer would raise the score significantly if the retinoblastoma experiments were eliminated.