Development of stem cell therapy for the treatment of retinal degneration

Hereditary retinal disease and age related macular degeneration (AMD) are major causes of irreversible blindness in the UK and involve the loss of the light sensitive photoreceptor cells in the retina. The lack of effective treatments for these conditions means there is a requirement to develop new therapies. The replacement of lost photoreceptors by cell transplantation is one possible approach, but transplanted cells need to make functional connections with the host retina. We have recently discovered that transplantation of immature photoreceptor cells from the developing retina into mouse models of retinal degeneration results in the integration of new photoreceptors that form functional connections with other retinal cells and improve visual function in these blind mice. Having defined the type of cell that is effective for retinal repair we now need to increase the number of new cells that integrate into the retina and find ways of generating the optimal type of immature cell in the laboratory. The adult retina contains retinal stem cells with the capacity to give rise to new photoreceptors in a cell-culture dish and these are a potential source of cells for transplantation that would avoid problems of rejection of foreign tissue.

The aim of this proposal is to develop strategies to replace missing photoreceptors in mouse models of retinal disease by transplanting retinal stem cells following various manipulations in the laboratory to optimise their development. We will investigate whether appropriate cells for transplantation can be generated by the introduction of genes that alter the stem cells themselves, and whether the introduction of genes into the retina receiving the transplant promotes increased levels of cell integration and enhances the improvement in vision. By determining the conditions for effective treatment of animal models using stem cells derived from the adult eye, we aim to provide the basic framework for developing similar approaches to treat human disease.

Retinal degenerations are the leading causes of untreatable blindness in the Western world. Retinal repair by photoreceptor transplantation is a highly promising therapeutic approach. This proposal outlines a research programme designed to overcome several challenges facing the development of retinal cell transplantation therapies and is based on our recent research. In an MRC-funded study published in the journal Nature, we discovered that transplantation of immature rod precursor cells at a specific stage of development results in their integration and differentiation into rod photoreceptors that form synaptic connections and improve visual function in mouse models of retinal degeneration. This proposal aims to build on the novel concept that the ontogenetic stage of the donor cell is important for the success of transplantation. The four research objectives are: (i) to maximise the number of integrating cells. Increasing the number of integrating cells is likely to enhance improvements to visual function. We aim to optimise protocols for rod and cone transplantation and test whether modulating the outer limiting membrane, or the growth factor distribution, in the host retina enhances integration; (ii) to develop protocols for cone transplantation. As AMD involves degeneration of the cone-rich macular and most visual loss in retinitis pigmentosa is due to cone loss, cone transplantation may be of greatest clinical value. We will define the optimal ontogenetic stage for cone transplantation, adopting a similar experimental strategy as used to define optimal rod donor cells, and test whether newly integrated cones are functional in mice with cone defects; (iii) to determine the potential clinical application for photoreceptor transplantation. Our transplant studies indicate that transplanted rods survive and may enhance cone survival in models of retinal degeneration. We will determine if rod transplantation enhances survival of functional cones and quantify the effect of rod and cone transplants in longitudinal studies using a range of visual assessments including pupillometry, ERG and behavioural tests. (iv) to generate photoreceptor precursors from in vitro cultures of retinal stem cells derived from the ciliary margin of the adult eye. CM-derived cells are a promising source of optimal stage donor cells for transplantation and they raise the possibility of autotransplantation if they could be derived from a patient?s own eye. We will use viral vectors to express or suppress expression of key transcription factors known to be important for rod or cone generation and test whether CM-derived photoreceptor precursors are effective donor cells for transplantation.