Intraocular tumor formation of RB reconstituted retinoblastoma cells

It has been reported that replacement of a functional retinoblastoma (RB) gene in RB defective WERI-27 retinoblastoma cells results in complete loss of their tumorigenic potential in nude mice following s.c. injection. We have repeated the identical studies and found that although tumors did not develop s.c., the RB reconstituted cells, either soon after RB virus infection or after long term cultivation, consistently produced tumors when injected intraocularly. These tumor cells, when reestablished in culture, were found to retain a normal RB protein as determined by direct Western blotting and immunocytochemical staining. The tumors, however, occurred with a longer average latency period and with less frequency compared to those produced by the parental RB defective cells. Our results suggest that reintroduction of the RB gene into WERI-27 cells reduces but does not completely suppress their tumorigenic potential. Since retinoblastoma is an eye tumor it also provides further documentation that the use of an orthotopic injection site can be critical when determining the tumorigenicity of a given cell type.