Human retinal cells have survived when transplanted into the eyes of monkeys to restore function and repair a part of the eye implicated in macular degeneration. This exciting development is a step towards a cure for a type of blindness that affects over 200 million people worldwide.

Blindness or vision loss is a condition with a horde of causes where the affected are unable to see anything, including light. Vision loss occurs when part of the eye is damaged by a disease or an abnormality. Moreover, depending on the specific eye disease, functional vision can be impaired in different ways.

The most recent findings from the WHO states at least 1 billion people suffer from vision impairment. Remarkably, 200 million of these cases are caused by retinal pigment epithelium (RPE) dysfunction, such as macular degeneration. The retinal pigment epithelium is a layer of pigmented cells in the retina essential for vision. Sadly, once this layer is damaged there is no cure for the vision loss incurred. This means the only treatment option available is aimed at slowing disease progression.

A step towards curing blindness

Now, a study from researchers led by A∗STAR, Singapore transplants human retinal cells into the eyes of monkeys, where they survived and flourished to restore the RPE layer. The team states their study is an important early step in treatment for blindness caused by RPE dysfunction. The opensource study is published in the journal Stem Cell Reports.

Previous studies show the retinal pigment epithelium (RPE) is thought to be where macular degeneration, a common condition that affects the middle part of your vision, begins. This crucial layer of cells next to the retina serves as a bridge between the light-sensitive photoreceptors of the retina and a layer of blood vessels, called the choroid, below.

The RPE’s role is to nourish the nerve tissue of the retina and maintain its health by disposing of dead cells, secreting hormones, transporting cells, and modulating immune factors. Interestingly, disruption to the aforementioned functions is linked to macular degeneration and ultimately, vision loss.

To date, undifferentiated RPE transplantation for the treatment of vision loss disorders such as age-related macular degeneration has been promising. However, this treatment, which does not use stem cells, has limitations due to the uncertain survival of RPE cells delivered by cell suspension and the inherent risk of uncontrolled cell proliferation in the vitreous cavity.

The current study is the first to demonstrate the potential restoration of lost vision caused by RPE degeneration, using stem cell replacement therapy in a non-human primate.

A vision transplant

The clinical trial extracts retinal stem cells from donated human eyes which were then differentiated into RPE cells. Subsequently, these cells were transplanted into the eyes of monkeys to restore the RPE layer. To enable this, the RPE cells were first grafted onto PET scaffolds to be successfully implanted in the form of a patch underneath the macula in the eyes of monkeys.

Results show RPE patches transplanted into non-human primate’s eyes stably integrated for up to three months with no deleterious side effects. Additionally, the stem cell-derived RPE patch partially took over the function of the monkey RPE to support normal photoreceptor function. Data findings show these cells did not cause retinal gliosis or scarring.

Stem cell banks for vision restoration

The group states over 100,000 eyes are donated annually in the United States alone. Thus, an average of 500 million stem cell-derived RPE cells can be harvested from each globe. They go on to add, similar to the concept of cord blood transplants, RPE cell banks could be established to serve as an unlimited resource of precious human RPE. This would also include the possibility of donor compatibility matching to reduce the chance of immune rejection.

The team surmises they successfully demonstrated the feasibility and safety of adult retinal stem cell-derived RPE as a treatment for eye diseases such as age-related macular degeneration. For the future, the researchers state they hope to conduct studies using diseased non-human primate models, progressing onto clinical trials.

Source: NUS Yong Loo Lin School of Medicine

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