Routine growth and differentiation of primary retinoblastoma cells in culture

The lack of systems permitting the routine growth of primary retinoblastomas has been a hindrance in the study of basic properties of these neoplastic cells. Therefore, a new culture system has been developed in which all retinoblastomas, regardless of their origin (primary eye tumor and/or its metastasis, subcutaneous and/or intraocular xenograft from the nude mouse), showed consistent growth. Each tumor could be grown for an unlimited number of culture passages with the use of rat smooth muscle cell multilayers as a biologic substrate and human serum as a culture medium supplement. Several of the tumor lines were continuously grown for longer than 1 year. Labeling with [3H]thymidine for 16 hours demonstrated that between 15 and 40% of the retinoblastoma cells were labeled, depending on the individual neoplasm. Retinoblastomas were organized into clumps of cells that adhered to the smooth muscle cells. The tumor cells maintained a round morphology, and cell spreading was observed in only a few cases. Cultured retinoblastomas consistently showed spontaneous formation of well-differentiated Flexner-Wintersteiner rosettes if these structures were present in the primary eye tumor of the patient. Thus the culture system consistently permitted the growth of retinoblastomas and their photoreceptor cell differentiation.