[Regeneration of the retina using pigment epithelial cell transplantation]

At has been reported that transplantation of appropriate cells, growth factors, and/or extracellular matrix may help the regeneration of damaged tissues or organs. Some growth factors, such as basic fibroblast growth factor(bFGF), have been successfully transferred to patients with ischemic heart disease. Embryonic dopamine neurons were also transplanted into the brains of patients with Parkinson's disease successfully. We have also performed cultured auto iris pigment epithelial cell (IPE) transplantation into the subretinal space after removal of choroidal neovascularization in patients with age-related macular degeneration (AMD). Here, we report the results of auto IPE transplantation in 35 patients, who could be followed for more than 6 months. We also tried to apply cell transplantation to other retinal diseases by managing the transplanted cells as introduced growth factor genes. Auto IPE transplantation was performed after removal of choroidal neovascular membranes (CNV). Visual acuity wes improved by more than 0.2 log MAR in 18 of 35 patients (51.5%), it was unchanged in 11 patients (31.5%), and it was worsened in 6 patients (17%). No significant difference was observed in comparison to patients who underwent CNV removal only. However, unlike the previous reports, we found no patients showing rejection. We also found that the cultured transplanted cells never showed proliferation under the retina or in the vitreous cavity and concluded that cultured auto IPE transplantation can be performed safely without complications. Next, we examined whether cell transplantation can be expanded to other degenerative retinal diseases. One of our results showed that host RPE may play an important role against the transplanted cells in the subretinal regions. When we introduced bFGF gene into the cells, we found synexpression cluster of the genes in the cells. One of the most prominent movements among the genes was lysyl oxidase like-1 gene, which plays an important role in the maturation of the extracellular collagen and in cell attachment. However, when we examined the cell attachment on the culture plates after 12 hours of culture, no significant difference was observed between the cells with or without bFGF. Further, when we examined the area of the cells transplanted into the subretinal space of rats during successive follow-up using fluorescein marker (EGFP), no statistical significance was observed. The gene expression pattern may be different when we introduce different growth factor gene. No antibody production was generated against the growth factor gene introduced cells after cell transplantation. Further, when we made transgenic mice expressing bFGF or Axokine cDNA in the RPE of rd mice, no photoreceptor degeneration was observed. One of the reasons was suspected to be that bFGF was expressed systemically by the promoter of tyrosinase related-protein 1 gene and may lead to lethality. Another reason was suspected to be suppression of the function of Axokine by the down-regulation of the ciliary neurotrophic factor or its receptor gene. Conversely, when we produced photoreceptor degeneration by constant light damage in the rats, we found partial photoreceptor rescue by transplantation of the growth factor gene introduced RPE. We show here the possibility that growth factor gene introduced cell transplantation may be applied to retinal diseases, if we select appropriate cells and genes.