Loss or persistence of the differentiated state of simian virus 40-induced hamster tumor cells before and after serial passage in culture.

The transformed cells that arise from among the hamster epithelial and mesenchymal cells exposed to SV40 in vitro are, as a rule, fibroblastoid and pleomorphic rather than epithelioid. Moreover, the neoplasms that these transformed cells induce in the allogeneic host are spindle cell sarcomas and pleomorphic sarcomas rather than carcinomas. Since this phenomenon may result from cellular dedifferentiation in culture, to the extent that the anaplastic morphology and lack of specialized function can no longer suggest the cell or origin, we investigated the fate of the differentiated state of cells of three types of SV40-induced hamster tumors before and after serial passage in vitro. The tumors evaluated were three reticulum cell sarcomas, three osteogenic sarcomas, and two lymphosarcomas of B-cell origin. Our data demonstrate that reticulum cell sarcoma cells lose their morphological differentiation soon after the original tumors are dissociated into cell suspensions but preserve their phagocytic activity throughout their in vitro passage. Osteogenic sarcoma cells lose their differentiated phenotype and their capacity to form osteoid during but not before their serial passage in culture. Lymphosarcoma cells preserve their lymphoid morphology and their ability to produce immunoglobulin even after many in vitro passages. These results indicate that, in many types of SV40-induced tumors, neoplastic cell dedifferentiation, following serial passage in culture, is responsible to a great extent for the emergence of new cell phenotypes lacking in morphological and functional features characteristic of the cells originally transformed by SV40.