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Embryonic stem cell transplants to cure disorders found safe for long-term.

Scientists have provided the first evidence of the medium-term to long-term safety and tolerability of transplanting human embryonic stem cells (hESCs) in humans.

The hESC transplants were used to treat severe vision loss in 18 patients with different forms of macular degeneration appeared safe up to 3 years post-transplant, and the technology restored some sight in more than half of the patients.

According to co-lead author Professor Steven Schwartz from the Jules Stein Eye Institute, Los Angeles, USA, the results suggested the safety and promise of hESCs to alter progressive vision loss in people with degenerative diseases and marked an exciting step towards using hESC-derived stem cells as a safe source of cells for the treatment of various medical disorders requiring tissue repair or replacement.

In the two phase 1/2 studies, hESCs were differentiated into retinal pigment epithelium cells and transplanted into nine patients with Stargardt's macular dystrophy and nine patients with dry atrophic age-related macular degeneration, the leading causes of juvenile and adult blindness in the developed world, respectively. No effective treatments exist for both conditions, and eventually the light-receiving (photoreceptor) cells of the retina degenerate leading to complete blindness.

All participants were injected with one of three different doses of retinal cells (50 000, 100 000, and 150 000 cells) into the subretinal space (under the retina) of the eye with the worse vision.

Researchers suggested that the embryonic stem cells had the potential to become any cell type in the body, but transplantation had been complicated by problems including the risk of teratoma formation and immune rejection. As a result, immune privileged sites (that do not produce a strong immune response), such as the eye have become the first parts of the human body to benefit from this technology.

The study was published in The Lancet.