According to the World Health Organization (WHO), close to 2.2 billion people across the world face vision impairment of which close to half (1 billion) still lacks treatment or could have been prevented. These conditions include blindness, distance vision impairment or near vision impairment.
An example of degenerative eye disease is retinal degeneration with a loss of the neuronal connections and glial cells of the retina. As lost/damaged retinal ganglion cells or photoreceptors are not replaced easily, effective therapies to replace the tissue of the retina are yet to see the light of the day.
Looking at stem cell therapy, several types of stem cells have shown promise in repairing damaged retina. Neural stem cells (NSCs) can differentiate into neural and glial cells post-transplantation in animal models of traumatic brain injury and spinal cord injury. A team led by McGill reported in The European Journal of Neuroscience in 2012 that the NSC transplantation in the subretinal space in Royal College of Surgeon (RCS) rats (models of photoreceptor degeneration) exerted a protective effect on the photoreceptors and prevented cell death.
The secretion of various factors by mesenchymal stem cells (MSC) has promise in addressing retinal damage. According to Mead et al (2015), bone marrow-derived MSCs (BM-MSCs) secrete PDGF, NGF, BDNF and NT-3 that protect injured retinal ganglion cells and also promote the growth of neurites. Further, animal models of optic nerve transaction and glaucoma that received intravitreal transplantation of BM-MSCs showed the MSC-secreted factors protected the ganglion cells from death. Similarly, BM-MSC transplantation in animal models of retinitis pigmentosa showed that the viability of photoreceptors and retinal pigment epithelial cells was preserved. This shows the potential of using MSCs to augment healing via the secretion of paracrine factors.
A 2011 phase I trial reported that a single intravitreal injection of autologous bone marrow-derived mononuclear cells in patients with retinitis pigmentosa or cone-rod dystrophy showed no toxicity or structural changes for 10 months (Siqueira et al, 2011; Clinicaltrials.gov: NCT01560715).
A preliminary phase 1 clinical trial published in 2014 in Investigative ophthalmology & visual science (2014) reported the feasibility and safety of autologous intravitreal CD34+ cell administration in 6 patients suffering from different eye degenerative diseases such as retinitis pigmentosa, age-related macular degeneration and retinal vascular occlusion. No adverse effects such as inflammation or division of cells were reported and no worsening of the eye conditions was also noted after 6 months. Further exploration is being conducted at (ClinicalTrials.gov number, NCT01736059).
The use of stem cells have already shown potential in the treatment of a wide range of diseases; it is said that “the eyes are the windows to the soul”-degenerative eye diseases that are yet to see an effective treatment can “see light” with the use of stem cell therapy.
Mead, B., Berry, M., Logan, A., Scott, R. A., Leadbeater, W., & Scheven, B. A. (2015). Stem cell treatment of degenerative eye disease. Stem cell research, 14(3), 243–257. https://doi.org/10.1016/j.scr.2015.02.003
McGill T.J., Cottam B., Lu B., Wang S., Girman S., Tian C., Huhn S.L., Lund R.D., Capela A. Transplantation of human central nervous system stem cells — neuroprotection in retinal degeneration. The European Journal of Neuroscience. 2012;35:468–477.
Siqueira RC, Messias A, Voltarelli JC, Scott IU, Jorge R. Intravitreal injection of autologous bone marrow-derived mononuclear cells for hereditary retinal dystrophy: a phase I trial. Retina. 2011 Jun;31(6):1207-14. doi: 10.1097/IAE.0b013e3181f9c242.
Park, S. S., Bauer, G., Abedi, M., Pontow, S., Panorgias, A., Jonnal, R., Zawadzki, R. J., Werner, J. S., & Nolta, J. (2014). Intravitreal autologous bone marrow CD34+ cell therapy for ischemic and degenerative retinal disorders: preliminary phase 1 clinical trial findings. Investigative ophthalmology & visual science, 56(1), 81–89. https://doi.org/10.1167/iovs.14-15415