Image of monkey retinas showing the difference between geneticallymatched (lowerpictures) and unmatched eye stem cells. Researchers have found that eye stem cells can be transplanted between different individuals, which could helptreatment of age-related macular degeneration and other eye conditions in humans. RIKEN LAB PHOTO

IN research that may have positive implications for treating age-related eye diseases in humans, researchers in Japan have successfully transplanted retinal pigment cells derived from the stem cells of one monkey into the eyes of other monkeys without rejection, and without the need for anti-rejection drugs, according to a study published in Stem Cell Reports.

Researchers from Japan’s RIKEN Center for Developmental Biology have launched a clinical trial of stem cell transplants in people with age-related macular degeneration, an eye disease that causes vision loss with age. In order to avoid tissue rejection, they used induced pluripotent stem cells (iPSCs) that were created from the recipient’s own skin cells—a costly and tedious process.

First author Dr. Sunao Sugita from RIKEN said, “In order to make iPSC transplantation a practical reality, the current goal is to create banks of iPSC-derived tissues that can be transplanted into anyone as they are needed. However, immune responses and tissue rejection are big issues to overcome when transplanting tissue derived from other individuals.”

The research on monkeys was an investigation into whether it would be possible to transplant stem cells other than those created from the patient’s own cells.

The results of the study showed that this is possible as long as a set of cell proteins called major histocompatibility complexes (MHCs) are genetically matched between the host animal and the new retinal cells. MHCs are a set of cell-surface proteins that function in the immune system and are found in all cells.

To test whether MHC matching is a viable method, the team used retinal pigment cells that were grown from monkey iPSCs and transplanted the cells into the subretinal space in monkeys with either genetically matched or non-matched MHCs. The researchers found that these transplanted cells survived without rejection for at least six months in MHC-matched monkeys, without using any of the usually necessary anti-rejection drugs. In contrast, rejection was relatively quick in the MHC-mismatched monkeys. Furthermore, the researchers found that infiltration by inflammatory cells was only present in the transplanted grafts of the MHC-mismatched monkeys.

The research could expand treatment options for patients with age-related macular degeneration, and possibly other eye conditions as well, the researchers said.