The cell line RN33B transplanted to adult retina

Abstract: The thesis describes the neural precursor cell line RN33B transplanted subretinally to adult healthy and young dystrophic rat retina. The cell line is generated from E12,5 rat raphe nucleus and transduced with the temperature sensitive mutant of the Simian Virus 40 (SV40) large T-antigen. The transplanted cells can be detected by the reporter genes for beta-galactosidase (beta-Gal) and the green fluorescent protein (GFP). Immunosuppression with daily injections of cyclosporine A was used. The grafted precursor cells survived up to four months post-transplantation. The precursor cells integrated mainly into the inner layers of the retina. The host architecture was well preserved. However the grafted RN33B cells differentiated to glial cells, and mainly to oligodendrocytes, but not to neurons. An extensive migrational capacity of the cells was revealed. Early after transplantation the grafted precursor cells were shown to migrate from the subretinal space in between the photoreceptors to the inner retinal layers within 4 days. On whole-mounted retinas 8 weeks post-grafting the precursor cells occupied up to 68% of the host retina. It was demonstrated that the host glial cells response was moderate, however when immunosuppression was used with FK506 a less preserved host architecture and an intense glial response and subretinal fibrosis was demonstrated. When the RN33B cells were transplanted to dystrophic RCS rats at P21 and P35 it was found that six weeks later the retinas grafted at P21 revealed rescue of the remaining photoreceptors. However, if the dystrophic retinas were more severely degenerated as at P35, it was not possible to demonstrate any photoreceptor survival. In all experiments presented here it was revealed that many of the grafted cells maintained an immature proliferative stage long after transplantation. The conclusion drawn is that the RN33B cell line survives well in adult retina, integrate into the inner layers of the retina, migrate extensively within the host retina and maintain an immature profile or differentiate along the glial lineage. Immunosuppression with cyclosporine A is important to maintain a healthy host retina. The RN33B cell line grafted to dystrophic retina demonstrate a promoting effect if the retinal degeneration is not too severe.