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Early follow-up of first human embryonic stem cells transplanted into subretinal space shows promise
Lancet. 2012;doi:10.1016/S0140-6736(12)60028-2.
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The first human embryonic stem cells transplanted into humans demonstrated no signs of hyperproliferation, tumorigenicity, ectopic tissue formation or rejection after 4 months of follow-up, two studies showed.
The prospective trials evaluated subretinal transplantation of human embryonic stem cells derived from retinal pigment epithelium in one patient with Stargardt's macular dystrophy and one patient with dry age-related macular degeneration.
Controlled cell differentiation led to greater than 99% pure retinal pigment epithelium, and cells displayed normal behavior, losing pigmented cobblestone morphology while proliferating and then re-differentiating into a monolayer of polygonal cuboidal pigmented epithelium once confluence occurred. Lightly pigmented cells attached and spread in greater proportion than darkly pigmented cells.
While visual endpoints were difficult to establish, neither patient lost vision, and each seemed to show improvement. However, the authors highlighted that gains may have been caused by use of immunosuppressive drugs or a placebo effect. Notably, it is unknown whether the cells have reduced immunogenicity or will experience rejection without long-term immunosuppression.
To enhance safety, embryonic stem cells underwent extensive testing for animal and human pathogens before transplantation. Future research goals include treating patients earlier to potentially increase the probability of photoreceptor and central visual rescue.
"Our data show that the extent of [retinal pigment epithelium] maturity and pigmentation might substantially affect subsequent attachment and growth of cells in vitro," the authors wrote.