Light at the end of the tunnel growing

A successful stem cell transplant in a human patient with retinitis pigmentosa (RP) is becoming closer to reality than ever – and new research from the University of Oxford may prove to be just the breakthrough needed.

In her research, university PhD student, Dr Alona Barnea-Cramer, set out to solve three problems that plague research on transplants to replace photoreceptor cells, she told OT.

The first issue was that the processes that create stem cells often leave researchers with a mixture of cells that include the desired mature photoreceptors, but also unwanted immature cells that could cause harm to the patient.

The method used by Dr Barnea-Cramer, developed by biotech company Astellas, mean she is able to create human cells that are 90% mature photoreceptors – avoiding the need for cell sorting.

The second issue is that many transplantation studies trying to treat RP in mice are not clinically relevant.

In these studies, mice have many remaining photoreceptors in their eyes, she said. In this study, the mice had none of these cells left, similar to patients with late-stage RP.

“It’s a completely different challenge for the surgeon and a completely different environment for the transplanted cells to grow and survive in,” she explained.

In the third difference, Dr Barnea-Cramer’s work also compared the results between human stem cells from embryos and those derived from a patient’s own skin cells. “We can’t find any statistical difference in the behavioural results, the amount of cells or the rate they were maintained [after the transplant].”

With these key alterations, Dr Barnea-Cramer was able to successfully transplant photoreceptor cells into mice. The results were published in the journal Scientific Reports.

She described the partial restoration of vision in the mice as “amazing, especially considering they were transplanted with human cells.”

Other research into stem cell therapies for RP is further down the line, with the University of California, Irvine, recruiting candidates for a clinical trial last year.

The next step for the Oxford research is pre-clinical safety work, Dr Barnea-Cramer told OT.

A human clinical trial could be five years away, fellow paper author and University of Oxford ophthalmologist, Professor Robert MacLaren, estimated.

“Cell replacement of this nature may provide a promising therapy for patients who have lost their sight due to the degeneration of their photoreceptor cells. This is an important step towards creating transplantable human photoreceptors as well as novel evidence that these cells may have the potential for receptor replacement therapy in blind patients,” he concluded.

The University of Oxford research was funded by the Royal College of Surgeons, Edinburgh.

Image credit: Nissim Benvenisty