Human retinal progenitor cells as candidate therapy for retinitis pigmentosa

The targeted disease is retinitis pigmentosa (RP), is a severe form of blindness that runs in families. This disease is not overly common, yet represents an attainable near term target for stem cell therapy for a number of reasons: 1) RP destroys the light detecting cells of the retina but generally leaves the rest of the visual system and body unharmed, so the clinical goal is circumscribed; 2) RP is prototypical of degenerations of the nervous system, so a cure for this less common disease would accelerate progress towards new therapies for a range of more familiar conditions; 3) scientific research has shown that degenerating rods and cones can be spared in animals by transplanting particular types of stem cells, so the scientific feasibility of treating RP in this way has already been established in principle.

The therapeutic approach is to save the light sensing cells of the eye (rod and cone photoreceptors) in people going blind using a type of stem cell obtained from the immature retina, but not from early embryos. These particular stem cells from the retina, known as progenitor cells, are capable of rescuing photoreceptors from degeneration following transplantation to the eye. These same cells are also highly efficient at becoming rod photoreceptors and this provides another more sustained pathway by which they preserve the crucial cone photoreceptors. In addition, there is evidence that the stem cells themselves might become functional photoreceptors and thereby stabilize the retina by directly replacing the dying cells in the patient’s eye. Thus, transplanted stem cells could treat the targeted disease of RP in multiple ways simultaneously. Importantly, there are a host of reasons why clinical trials in the eye are easier and safer than most locations in the body. The eye is an important proving ground for stem cell-based therapies and provides a stepping stone to many otherwise incurable diseases of the brain and spinal cord.