Stem cells are immature cells that can both divide and differentiate into other tissues. Pluripotent stem cells can become virtually any cell type in the body, which gives them great versatility but also makes them less predictable.
Progenitors are stem cells that are more restricted. They have begun the differentiation process but are still immature and have yet to reach their final destination. Progenitor cells from the retina can differentiate into photoreceptors – rods and cones. However, they cannot become non-retinal cells, such as bone, fat or muscle.
When used therapeutically, retinal progenitor cells perform two important functions. First, they secrete growth factors that rescue damaged retinal cells and slow disease progression. These cells can also integrate into the retina and generate new rods and cones, replacing dying retinal cells and possibly reversing the course of the disease.
Because the eye is “immune-privileged,” the body does not see transplanted progenitor cells as foreign invaders and generates no immune response. As a result, transplant patients need not take immunosuppressive drugs, making the process safer and reducing the potential for side effects.