title: Ex vivo gene therapy using intravitreal injection of GDNF-secreting mouse embryonic stem cells in a rat model of retinal degeneration.
abstract: OBJECTIVE
  Safe and prolonged drug delivery to the retina is a key obstacle to overcome in the development of new medicines aimed at treating progressive retinal disease. We took advantage of the ability of embryonic stem cells to survive long-term in foreign tissue and used these cells to deliver neuroprotectant molecules to the retina of the rhodopsin TgN S334ter-4 rat model of retinitis pigmentosa (RP).
  
  
  METHODS
  Mouse embryonic stem (mES) cells, derived from the pluripotent embryonic stem cell line E14TG2a, were genetically engineered to oversecrete the glial cell-derived neurotrophic factor (GDNF). Cell suspensions, containing approximately 200,000 cells and expressing approximately 35ng/10(6) cells/24 h GDNF, were injected into the vitreous cavity of TgN S334ter rat eyes at postnatal day 21 (P21) without immunosuppression. Histological and immunofluorescence imaging was used to evaluate photoreceptor survival up to P90. Local (vitreous) and systemic (serum) concentrations of GDNF were determined and ocular side effects were monitored.
  
  
  RESULTS
  Green fluorescent protein (GFP)-expressing mES cells were observed on the inner limiting membrane of the retina in retinal flatmounts up to P90. In cryostat sections at P45, some GFP-expressing cells had integrated into the inner retina, but did not migrate into the outer nuclear layer. After an initial lag period, the photoreceptor cell counts were significantly higher (p< or =0.05) in animals treated with GDNF-secreting mES cells than in untreated animals, principally in the peripheral retina. Several adverse side effects such as tractional detachments and areas of hyperplasia were seen in a minimal number of treated eyes. Abnormally high levels of GDNF in the peripheral circulation were also observed.
  
  
  CONCLUSIONS
  ES cells engineered to secrete GDNF exerted a neuroprotective effect for at least three months on retinal structure in the TgN S334ter rat model of retinal degeneration. Immunosuppression was not required for this. Several adverse effects were identified which require further investigation to make cell-based delivery of neuroprotection a viable clinical strategy.
authors.affiliation: Department of Clinical Neuroscience, Faculty of Medicine, Imperial College London, London, UK. k.gregory-evans@imperial.ac.uk
authors.forename: Kevin
authors.initials: K
authors.lastname: Gregory-Evans
authors.forename: Francis
authors.initials: F
authors.lastname: Chang
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Hodges
authors.forename: Cheryl Y
authors.initials: CY
authors.lastname: Gregory-Evans
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002470:Cell Survival; D004195:Disease Models, Animal; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism* / Q000637:transplantation; D015316:Genetic Therapy / Q000379:methods*; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000032:analysis / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006651:Histocytochemistry; D007267:Injections; D051379:Mice; D018696:Neuroprotective Agents / Q000032:analysis / Q000097:blood; D051381:Rats; D012160:Retina / Q000378:metabolism* / Q000648:ultrastructure; D012162:Retinal Degeneration / Q000473:pathology / Q000628:therapy*; D012174:Retinitis Pigmentosa / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D018709:Statistics, Nonparametric; D033581:Stem Cell Transplantation; D014162:Transfection; D014822:Vitreous Body / Q000737:chemistry
chemical_list: D051100:Glial Cell Line-Derived Neurotrophic Factor; D018696:Neuroprotective Agents; D049452:Green Fluorescent Proteins