Best-corrected visual acuity, monitored as part of the safety protocol, improved in ten eyes, improved or remained the same in seven eyes, and decreased by more than ten letters in one eye, whereas the untreated fellow eyes did not show similar improvements in visual acuity. 13 (72%) of 18 patients had patches of increasing subretinal pigmentation consistent with transplanted retinal pigment epithelium. Adverse events were associated with vitreoretinal surgery and immunosuppression. There was no evidence of adverse proliferation, rejection, or serious ocular or systemic safety issues related to the transplanted tissue. The studies are registered with, numbers NCT01345006 (Stargardt's macular dystrophy) and NCT01344993 (age-related macular degeneration).

Transplanted patients were followed up for a median of 22 months by use of serial systemic, ophthalmic, and imaging examinations. Three dose cohorts (50,000, 100,000, and 150,000 cells) were treated for each eye disorder. In the USA, two prospective phase 1/2 studies were done to assess the primary endpoints safety and tolerability of subretinal transplantation of hESC-derived retinal pigment epithelium in nine patients with Stargardt's macular dystrophy (age >18 years) and nine with atrophic age-related macular degeneration (age >55 years). We report the medium-term to long-term safety of cells derived from human embryonic stem cells (hESC) transplanted into patients. Since they were first derived more than three decades ago, embryonic stem cells have been proposed as a source of replacement cells in regenerative medicine, but their plasticity and unlimited capacity for self-renewal raises concerns about their safety, including tumour formation ability, potential immune rejection, and the risk of differentiating into unwanted cell types.

Steven d schwartz md