Testing the Safety of Induced Stem Cell Therapies

February 5, 2014 - To restore sight to a damaged retina, one promising strategy is to replace the damaged cells with new ones. One way to do this is to start with stem cells and transform them to create new retinal cells. Learn more about type of therapy in our stem cell therapy fact sheet.

In the last few years, scientists have demonstrated that that retinal cell transplants are possible in mice, and the first clinical trials using cells derived from stem cells have started in humans. Right now, the only transplants being tested in these trials are of retinal pigmented epithelium (RPE) cells, the foundation cells of the retina, which are damaged in macular degenerations such as age-related macular degeneration and Stargardt disease. Although RPE cells are not directly responsible for vision, they are essential to the health of the retina, and early studies suggest that restoring them may have a positive effect on vision in these two conditions.

The trials now underway in the USA use RPE cells grown from embryonic stem cells. However, there is a possibility that a person’s body could have an immune reaction and reject cells grown in this way, since they are foreign tissue from unrelated donors. As well, there continue to be ethical concerns about the use of stem cells derived from human embryos.

To avoid the use of embryonic cells, scientists in Japan have developed a process for producing “induced pluripotent stem cells (iPSC).” This process involves taking cells from the skin or inner cheek and forcing them to regress to an immature state – a stem cell. These cells can then be used to make RPE cells or other needed cell types, such as rod and cone photoreceptors.

Scientists in Japan are now preparing for a human clinical trial of RPE cell transplants derived from ipSCs. Because of the way these cells have been manipulated more than embryonic cells, to make them revert to a more primitive state, there is some concern that there might be a greater risk of cancer with ipSCs than with normal embryonic cells. Retinal cell transplantation is such a new science that there is not yet a standard way to assess this risk.

Earlier this month, the Japanese scientists published a series of studies in the journal PLoS ONE, demonstrating that these cells were safe for transplantation. They injected RPE cells created from iPSCs into mice that lack functioning immune systems, and so are at high risk of developing cancers. The team injected cells into the retinas of these mice, but since a mouse’s eye is so small, they also tested by injecting a larger, more human-sized dose of the induced RPE cells in a bubble under the skin.

In 15 months of monitoring the larger injections (and 6-12 months of following mice with the smaller retinal injections) no tumours developed. The scientists published an extensive discussion of the methods used in this testing, in hopes of creating new standards for testing the safety of cells for retinal transplantation in the future.

Use this link to learn more about the planned Japanese trial.

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