Iris pigment epithelial cells transplanted into the vitreous accumulate at the optic nerve head

Iris pigment epithelial (IPE) cells have mainly been investigated in the past for their proposed potential to rescue or even replace degenerated retinal pigment epithelial (RPE) cells after subretinal transplantation in patients with age-related macular degeneration (AMD). More recent reports have characterised the IPE cell as a potent source of trophic factors and cytokines. In our study we investigated the spatial distribution of IPE cells that were injected into the vitreous instead of being injected subretinally.

IPE cells from Long Evans rats were isolated and injected into the vitreous cavity of Wistar rats without preculturing. Free melanin granules were injected into the vitreous in the same manner. After a period of 2 months, eyes were prepared for histological analysis. Localisation of the injected IPE cells was defined by topographical mapping of the analysed sections.

PVR was not observed in any eye. In 8 of 10 injected eyes, IPE cells had accumulated in the prepapillary region. In 2 of 10 eyes, no IPE cells could be detected. The injected melanin granules also accumulated at the optic nerve head, indicating that this is most likely a passive process. In sections of the papillary region containing retinal vessels, the IPE cells seemed to have migrated into the superficial tissue of the optic nerve head.

Our results demonstrate a way to access the optic nerve head easily and securely without the danger of damaging its fragile structure. This could have important implications for new therapeutic strategies in ocular neurodegenerative diseases like glaucoma. New prospects in gene therapy will require further characterisation of the potential of the IPE cell to produce neuroprotective trophic factors at the optic nerve head.