Retinitis pigmentosa (RP) is a severe form of blindness that often runs in families, but other times arises spontaneously or from recessive genetic errors. This disease is rare, 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 in the back of the eye, yet 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 saved in animals by transplanting particular types of stem cells, thus the scientific feasibility of treating RP in this way has already been established in principle. The therapeutic approach pursued by our team is to save the light sensing cells of the eye (rod and cone photoreceptors) by transplanting a type of stem cell known as a progenitor cell. These cells are capable of saving photoreceptors from degeneration following transplantation to the eye. These same cells are also highly efficient at producing new 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 therefore an important proving ground for stem cell-based therapies and provides a steppingstone to many otherwise incurable diseases of the brain and spinal cord.
As part of the current project, our cell type of interest has now been manufactured under specific conditions ensuring that pharmaceutical standards are met (Good Manufacturing Practice, GMP). The resulting GMP cells have been tested in the laboratory to verify that they are free from microbial contamination and chromosomal defects. The cells are currently being tested in animals for safety and to make certain that they are therapeutically potent. When this testing is completed, an application will be made to the FDA seeking approval for the use of these cells in early clinical trials. Following approval, a small number of patients with severe RP will be injected with cells in their worse-seeing eye and followed clinically for a specified period of time to determine the safety and effectiveness of the treatment.