Chairperson: R. MacLaren UK, S. Wolf SWITZERLAND
08.30 | D. Fischer GERMANY
Subretinal microbeads - a stem cell based intraocular delivery systemview abstract- click here
Microbeads are genetically engineered and microencapsulated human mesenchymal stem cells with the potential as slow release system for biologicals in the eye. We studied the impact of subretinal microbead implantation on retinal integrity and monitored viability of the xenogenic cells in the mouse eye by noninvasive retinal imaging (Spectralis™ HRA+OCT) and upon the end of the study by light and electron microscopy.
The implanted GFP-marked cells encapsulated in subretinal microbeads remained viable over a period of up to 4 months. Studies on the retinal integrity following implantation showed focal damage due to the surgical implantation, as well as GFAP upregulation and opsin mistargeting in the immediate surrounding of microbeads.
The accessibility for routine surgery and its immune privileged state make the eye an ideal target for release system implants for therapeutic substances, including neurotrophic and anti-angiogenic compounds or protein based biosimilars. Microencapsulated human stem cells, such as the microbead system, promise to overcome limitations inherent with single factor release systems, as they are able to produce physiologic combinations of bioactive compounds.
08.48 | M. Karl GERMANY
Age-dependent neuronal regeneration of mouse retinaview abstract- click here
Our retina does not regenerate spontaneously upon damage. This is in contrast to species like fish and birds where Müller glia cells de-differentiate into progenitor-like cells and regenerate up to all types and numbers of retinal neurons. Recent studies suggest that in mammalian retina a regenerative program could be reactivated in and ex vivo. We investigated in detail that after retinogenesis is complete the still young Muller glia de- differentiate and re-enter the cell cycle at higher numbers compared to the adult retina. Our data suggests that in postmitotic Müller glia developmental mechanisms establish roadblocks to the regenerative program. We identified various genes related to the regenerative program in fish and chick that are activated in Müller glia in young retina at higher levels compared to adult. Further, we observed a larger number of Müller glia derived neuronal cell progeny. We seek to find out whether age-related mechanisms restrict regeneration to a gliotic response in mammals.
09.06 | M. Singh UK
Reconstruction of the outer nuclear layer in end-stage retinal degeneration view abstract- click here
Patients who are blind from retinal degeneration often present at advanced stages of disease when the retinal outer nuclear layer of photoreceptors has been lost. Hence, one candidate strategy for treatment is by photoreceptor transplantation with the aim of reintroducing light-sensing cells to the retina. Once placed in the severely degenerate subretinal space, the replacement cells would need to organise into a polarized layer in the correct anatomical location, appropriately develop outer segments, and reconnect with host bipolar cells. Outer nuclear layer reconstruction may in future be a way to restore visual function to patients with end-stage retinitis pigmentosa and other retinal degenerations.
09.24 | M. Ader GERMANY
Transplantation of cone-like photoreceptors into the adult mouse retinaview abstract- click here
Visual impairment and blindness due to degeneration of photoreceptors represent one of the main causes for disability in industrialized countries. Cell-based strategies by means of cell transplantation for the replacement of lost photoreceptors constitute a promising therapeutic option. Indeed, recent studies provided evidence that immature photoreceptor precursor cells have the potential to correctly integrate into the adult mouse retina where they developed into mature photoreceptors containing discs-filled outer segments and synaptic contacts to endogenous second order neurons. Human vision mainly depends on cone photoreceptors as these cells are required for daylight vision. Although cones represent collectively only ≈5% of all photoreceptors in the human eye, they are indispensable for focused vision and color discrimination. However, currently most transplantation studies focused on rod photoreceptor grafting due to the availability of sufficient amounts of donor cells that can be isolated from the rod-dominant retina of mice, leaving the transplantation of cone photoreceptors not well investigated. Indeed, the low number of cones within the mouse retina limits a systematic evaluation of cone transplantation. Interestingly, the retina of Nrl-deficient mice is depleted of rods and consists instead solely of cone(-like) photoreceptors. Therefore we used Nrl-deficient mice as a comprehensive source for transplantation experiments aiming to replace degenerated cones with cone-like cells to evaluate their capacity to integrate into the adult mouse retina and to generate mature, light-detecting photoreceptors.
09.42 | V. Enzmann SWITZERLAND
Bone marrow-derived stem cell treatment for retinal degeneration view abstract- click here
Age-related macular degeneration (AMD) is becoming increasingly prevalent. Despite recent advances no therapeutic approach achieves significant recovery of lost vision for patients with its dry form. Atrophy of the retinal pigment epithelium (RPE) is a critical feature of the disease. Therefore, the use of stem cells has been recently proposed to replace dysfunctional RPE to prevent or reverse degeneration of the overlying photoreceptors. Bone marrow-derived stem cells (BMSC) were studied by us for integration, differentiation and the potential to rescue vision after transplantation into the subretinal space of mice with sodium iodate (NaIO3) induced retinal degeneration. This model mimics symptoms of dry AMD as the substance specifically targets the RPE followed by apoptosis of photoreceptors. The focus of our studies has been on the effect of in vitro pre-differentiation of the BMSC towards the RPE lineage before subretinal transplantation of the BMSC.
BMSC cocultured with adult RPE cells were positive for RPE65 and bestrophin indicating pre-commitment towards the RPE lineage. Measurements of visual functions showed improved visual acuity after transplantation of cocultured BMSC compared to freshly harvested BMSC and to the contralateral eye. Morphometric measurements however showed no significant increase in retinal thickness within the transplantation area. Immunohistochemistry revealed expression of RPE65 and bestrophin by the transplanted RPE-committed BMSC. In contrast, uncommitted BMSC expressed mainly GFAP in the subretinal space.
Pre-differentiated BMSC integrate into the retinal structure and express RPE marker after transplantation into the damaged subretinal space. The procedure led to improvement of visual function in individual cases but not in the general population. BMSC might therefore represent a new, allogeneic source for regeneration therapy in degenerative diseases of the retina.
10.00 | R. MacLaren UK
Restoration of vision with the subretinal electronic retinal implant and relevance to future stem cell therapies view abstract- click here
Photoreceptor replacement by transplantation is likely to be one of the first applications of stem cells to treat blindness. To be effective, stem cell-derived photoreceptors would most likely need to be transplanted into the subretinal space and interact with host bipolar and horizontal cells in order to transmit light induced visual signals to the inner retina and hence via the optic nerve to the central visual relays. Currently a number of promising developments have been seen in animal models of end-stage retinal degeneration, most recently with regeneration of the outer nuclear layer in the adult rd mouse, which is the laboratory equivalent of end-stage retinitis pigmentosa with no light perception. In parallel with the stem cell work we have also seen significant advances with electronic retinal implants. The subretinal electronic retinal implant developed by Retina Implant AG has been shown to restore sight to blind patients to enable them to read again in some cases. There is therefore a lot to learn from the subretinal electronic implant that is relevant to understanding how patients might see again with stem cell treatments and these technologies must be viewed in parallel. In this presentation I will give an outline of our initial experience with the subretinal implant Alpha-IMS as part of multicentre clinical trial sponsored by Retina Implant AG and led by Eberhart Zrenner in Tübingen. The device has worked in all six patients so far implanted and their descriptions of the vision that has been restored provides us with an insight into what might be achieved in future using stem cells.
10.18 | Discussion
10.30 | End of Session