New Faculty II
Age-related macular degeneration (AMD) is the leading cause of blindness in California and the United States, for which there is no cure. It has devastating effects on the quality of life as it makes it impossible for affected individuals to read and drive, and has become a major public health concern in the rapidly expanding aging population of California. AMD is particularly amenable to potential stem cell-based therapy because the affected areas of retinal pigment epithelium (RPE, the tissue primarily affected by the disease) and the overlying retina are very small, may be directly visualized, and transplantation of stem cells could be performed by direct injections using currently available surgical techniques. A number of recent studies suggest a great potential for using various populations of stem cells to improve the morphological and functional capacity of RPE and the retina. However, we are yet to develop a stem cell-based approach for the management of specific retinal diseases such as AMD, and to establish clinically acceptable treatment protocols. In addition to human embryonic stem cells, adult, patient-own stem cells may provide the safest approach in patients with AMD at least for the near future. This implies using adult stem cells obtained from an easily accessible and abundant tissue source such as bone marrow from the same patient, which greatly increases their immune compatibility and overall safety. Following their isolation, these cells may be injected into the eyes of patients with age-related macular degeneration into the areas affected by the disease. There are two major obstacles that prevent successful therapeutic retinal/RPE regeneration in patients with AMD using stem cells due to the wide developmental gap between the immature stem cells and mature adult recipient tissues. Thus, when transplanted into adult tissues, these immature cells have a relatively low potential for developing into adult cells bearing the desired retinal/RPE function and have relatively low efficiency to engraft within adult microenvironment. We propose to develop a robust, convenient and rapid “natural incubator” approach using chicken embryos for partially differentiating human stem cells of various origins into high-quality mature precursors of retinal photoreceptors and RPE cells suitable for their therapeutic transplantation in adult ocular tissues. Embryonic chick eye provides an in vivo habitat for the donor stem cells to follow the natural developmental program. We also propose to modulate interactions between donor stem cells and the host ocular microenvironment to enhance the efficiency of stem cell incorporation using laser irradiation. Our proposed studies provide the foundation for future development of an efficient stem cell-based management strategy for AMD and, therefore, have important therapeutic implications for the leading cause of blindness in California and the United States.
Statement of Benefit to California:
My proposed research focuses on the development of stem cell-based therapeutic approaches to age-related macular degeneration (AMD) and other diseases in which the deterioration of retinal pigment epithelium (RPE) and retina plays a significant role. It will benefit the citizens of the state of California in several important ways. AMD is the leading cause of blindness in the United States, and in California, and it is currently incurable. It has devastating effects on quality of life and independence, and is becoming a major public health concern as California’s population ages, and the state’s older citizens live longer, and require more assistance in the activities of daily living. The socioeconomic and emotional impact of AMD is tremendous because the disease affects central vision, limiting the ability of those who suffer from it to drive or read. Identifying a successful treatment would allow tens of thousands of elderly Californians to enjoy a more functional, productive, and enjoyable years beyond retirement. Several studies have suggested the great therapeutic potential of various populations of embryonic and adult stem cells derived from the bone marrow for regeneration of retina and/or RPE. Stem cell transplantation has already received considerable attention as a novel neurotherapeutic strategy, but so far, little work has been devoted to stem cell therapies for specific retinal disorders. We have yet to develop a stem cell approach for the management of specific retinal diseases like AMD, or to establish clinically acceptable treatment protocols. While human embryonic stem cells have high regeneration potential, patient-specific transplantation of adult stem cells obtained from patient’s own bone marrow has certain practical advantages. Most importantly it eliminates the need for immunosuppressant drugs necessary in transplantation of cells or tissue from another individual, and carries no risk of tumor formation. The research proposed in the current application to the California Institute for Regenerative Medicine will utilize the chick embryonic ocular model to lay the groundwork for the use of the various populations of human stem cells as a potential therapy for the blinding retinal degenerative and age-related disorders. This will benefit California’s citizens by speeding our progress towards a safe and effective treatment for AMD and other related diseases affecting vision.
This applicant proposes to use the developing chick retina as an incubator for stem cell differentiation in the eye. Specifically, the developing chick eye will be used as an incubator for the in vivo differentiation of stem cells into retinal pigmented epithelium and retinal progenitor cells. The applicant proposes to use both human embryonic stem cells and human bone marrow derived mesenchymal stem cells in this model, and to determine the survival, differentiation and integration of these cells in the chick eye. In addition, the applicant proposes to assess the influence of mechanical injury of the eye on subsequent differentiation and functional improvement of grafted stem cells. This is an innovative approach to providing a supportive microenvironment for the differentiation of retinal progenitor cells that offers a provocative promise for success. The applicant based the approach on recent findings for spinal cord xenografts, and presents pilot data in support of the ability of labeled progenitors to incorporate into host retina. However, reviewers noted that the lack of defined functional end-points after implantation is a major weakness, and the applicant did not direct sufficient effort to addressing the clinical relevance of the approach. They also felt that the applicant’s research experience in stem cells was not very strong, and the mentoring plan did not compensate for this lack of experience. Institutional support for stem cell research was felt to be good, but support of this particular applicant was only standard, and the support letters did not generate enthusiasm. The approach was described as innovative but the proposal was ultimately judged to be unsatisfying. Reviewers highlighted two major problems with the proposed strategy. First, there is no control over the cell types induced within the chick retina, so if induction does occur it is likely that more than one cell type will be induced. The preliminary data do not give enough information about the types of cells that the applicant expects might be induced, or their frequencies, to determine if this strategy will work and how it will be (functionally) analyzed. The second problem is recovery of pure enough, and significant numbers of, induced cells of a particular type for future engraftment. The applicant acknowledges that this is beyond the scope of the grant. However, without some evidence of a strategy for this it is not clear that the proposal offers any advantage over current work. In fact, it appears that the proposed strategy has disadvantages relevant to current stem cell work in the area of retinal regeneration. In addition to the major criticisms listed above, reviewers commented that the studies are based solely on morphological data, which may have little or no relevance to functional improvement following cellular implantation. There are numerous instances where transplanted cells can display significant morphological survival, differentiation and integration into the brain and yet do not induce significant functional benefit. Other criticisms included the observation that the applicant proposes to use fluorescent reporters of RPE cell fate, but most fluorescent reporters are quenched by the melanin in the RPE cells; and that experiments proposed to test the cells’ pluripotency were considered inadequate. A final question was how the data obtained from the embryonic eye will be used to guide translational work in adult eye, particularly in humans. The embryonic retina represents a fertile environment for looking at survival, differentiation and integration of grafted cells, but is substantially more permissive to these events that the adult eye. The applicant does not address how this work will be taken forward into adult tissues, which significantly weakened the enthusiasm for this proposal. The applicant is an accomplished retinal surgeon and assistant professor of ophthalmology, and has had significant training in molecular biology. However the applicant has generated few publications and no significant research funding outside of institutional start-up funds. Reviewers were concerned that the applicant has no prior experience in stem cell biology as most prior work has been focused on basic biology of retinal cells. Although good mentors are identified in the application, the overall assessment was that the mentoring was not sufficient to overcome the applicant’s lack of experience. The institution has a strong stem cell research program and is committed to this program’s success. One reviewer commented that support for the applicant was substantial and includes an excellent start-up package, research facilities appropriate to the work, and adequate space. However, the letter of support was surprisingly generic, and it was not clear that any of the applicant’s clinical time would be reduced to accommodate the proposed research.