Human Limbal Epithelial Stem Cell Conversion into Photoreceptors for Treatment of Retinal Degeneration
New Faculty II
Few people know that age-related macular degeneration (AMD) is the leading cause of blindness of people over 55 in the US. More than 10 million Americans are affected by this irreversible disease and the risk of getting macular degeneration reaches nearly 30 percent in those over age 75. Former Director of the National Eye Institute publicly stated that AMD will soon take on aspects of an epidemic. The disease affects the central part of the retina – light-sensitive tissue located inside the eye. Retina is a multilayer tissue that contains light-perceiving neuronal cells called photoreceptors. These cells are connected to other neurons in the retina that process the image information and send it to the brain via the optic nerve. The destruction of photoreceptors and supporting retinal cells is progressive in AMD and no effective therapy to recover lost vision exists. Ophthalmologists can slow down abnormal vessel growth and scarring, but replenishing lost retinal cells to recover vision is not yet possible. The discovery of stem cells opened new possibilities to rebuild aging and damaged tissues throughout the body. We propose a procedure by which to convert stem cells present on the surface of the eye into light-perceiving neurons. These stem cells are present in a ring-shaped structure located on the front surface of the eye around the cornea. This structure, called limbus, is an active factory where stem cells convert into surface cells used to cover the cornea and lost as we blink. These multipotent stem cells have the same origin as the internal stem cells that become retina during eye development, and have the same latent neuronal program that can be activated. Stem cells in general conform to the environment of the organ they live in and follow the commands of the “niche”, the surroundings, to differentiate into specialized cells needed at that particular location. We propose to take stem cells from the limbus and free them from their niche, provide stimulants and growth factors that signal the need for nerve cells, and allow them to grow into photoreceptors. We then intend to transplant these new photoreceptors into retina and stimulate their integration and activation of light perception. Many parts of this research have already been successful in mice. For our research we plan to use part of human tissue donated to eye banks for corneal transplantation that is currently being discarded after surgery, thus avoiding many ethical and technical issues associated with other stem cell use. We plan to develop a therapy where a small amount of eye surface tissue from a patient is grown and converted into photoreceptors and given back to the same patient, avoiding problems of rejection and immunosuppression. This revolutionary therapy will make it possible to restore vision in people with macular degeneration.
Statement of Benefit to California:
Age-related macular degeneration is promising to become a very significant health problem and public burden by year 2025. Given lack of a therapy with the potential to return lost vision to the patients with this disease at the present time, human suffering due to blindness caused by AMD is already alarming many ophthalmologists such as myself. The State of California will benefit immensely from this breakthrough research and subsequent novel therapy, in both human and fiscal aspects. The availability of therapy to restore retinal structures will reinforce California's leadership position in stem cell research and regenerative medicine. Potential for commercialization of this therapy and making it available to millions of people would bring significant private funding resulting in significant revenue and growth of stem cell biotechnology sector. Further extension of findings of this project to other tissues, especially other parts of nervous system, can amplify these beneficial effects several times over. Successful therapy for the most common blinding disease of aging population of the State of California would also significantly decrease healthcare and social care burden while improving the quality of life for the patients.
This proposal focuses on isolation and differentiation of corneal limbal stem cells for use in cell therapy. The first aim is to identify limbal stem cells in the human eye and to generate/optimize culture conditions for their long-term expansion. In the second aim, the applicant proposes to transdifferentiate these cells into neural progenitors that, in aim 3, will be differentiated into functional retinal cell types. In aim 4, the applicant proposes to implant these cells into rodent retinal slice models and in vivo into the eye. This is a well-written proposal from an ophthalmic surgeon who is addressing a meaningful clinical question. Reviewers were very supportive of the applicant’s institution, and commented positively on the clinical skills and experience of the applicant. Consensus achieved during the review, however, was that the research plan was immature, especially since the applicant did not provide adequate preliminary data to justify the scientific hypothesis or evidence that the applicant or the laboratory could complete the experiments proposed. There is very little evidence provided in the application that the limbal cells differentiate into retinal cells or that there is any significant advantage to using limbal stem cells over ciliary margin stem cells or iris stem cells (these cells can be obtained from humans and are capable of generating retinal neurons and photoreceptors) or other stem cells. Although the work in this proposal is novel and innovative, it is not obvious that it is feasible or that there is a clear advantage to deriving retinal cells from limbal stem cells. Reviewers agreed that the strength of the research plan is that donor tissue is readily available for these experiments. One of the major problems cited with this work, however, is that the data regarding the differentiation of limbal stem cells to functional photoreceptors is based on a single paper, which has not been replicated by other groups or by the applicant’s lab. This a serious flaw as the entire proposal hinges on achieving this differentiation. Additionally, it is clear that the applicant has very little real understanding of some of the difficulties of working with these types of cells and generating high quality cultures suitable for in vivo transplantation. The applicant proposes conditions for culturing limbal stem cells, but cites neither previous work nor any preliminary data from the applicant’s lab that would suggest that these are optimal culture conditions. Reviewers therefore doubted the feasibility of the project. The applicant is a skilled ophthalmic surgeon with excellent training who completed strong work as a graduate student. The mentoring team of four faculty members is impressive in terms of their breadth of topic areas and experience. However, reviewers commented that the applicant has not been in the lab since completing a PhD over ten years ago, and it is not clear that the applicant has a running laboratory at this time. In addition, the applicant’s experience is in RNA localization, not in cellular or stem cell biology. The career development plan was described as fairly standard with the usual goals of obtaining funding and high quality publications. There is no real detailed plan as, for example, the plan is completely lacking in milestones and any defined targeted goals. The institution offers excellent facilities and environment, with a minimum of 33% protected time for research. However, two reviewers commented that it sounds as if the applicant may get independent lab space only if this application is funded. Another reviewer noted that very little information was provided regarding the institution’s long-term plans in regenerative medicine. In summary, reviewers were not confident about the feasibility of the research plan. Protocols for growing limbal stem cells and differentiating them into retinal cells are not well-established, and reviewers commented that the applicant did not provide convincing evidence that this group had the research skills to complete the experiments proposed.