Neuronal and photoreceptor differentiation of retinoblastoma in culture.

This study describes an in vitro system, which favors attachment and differentiation of primary retinoblastoma cells. Indeed, tumor cells from primary retinoblastomas were successfully grown as long-term monolayer cultures, using collagen type-1 coated flasks, preincubation of tumor cells in fetal calf serum and a medium richly supplemented with serum. This reliable system allowed growth and attachment and induced differentiation towards neuronal and photoreceptor morphology. Each of the nine tumors studied showed substantial cell proliferation and differentiation. Cells with glial characteristics were observed in lower numbers. Furthermore, in five cell-lines, some cell clusters showed pigmentation characteristic of pigment epithelial cells (PE). By electron microscopy, a significant proportion of cells showed conventional neuronal differentiation; others formed typical Flexner-Wintersteiner rosettes with individual photoreceptor cells showing a more highly differentiated pattern quite similar to fleurette inner segments. Immunohistochemical studies did not reveal evidence of transition between undifferentiated retinoblastoma cells and glial cells, although foci of multipolar cells were found resembling glial elements and containing glial fibrillary acidic protein. Thus no definite sign of glial differentiation was observed. These results show that most primary retinoblastoma cells can grow in attachment culture and differentiate into at least two distinct morphological cell types. This study also offers a potentially rewarding system to analyse the factors controlling growth and differentiation of human tumor cells in vitro.