An epithelioid variant of the BHK21 hamster fibroblast line and its transformation by polyoma virus.

An epithelioid variant, which forms characteristic colonies in soft agar medium, has been isolated from the BHK21/13 line of hamster fibroblasts. After infection with a high multiplicity of polyoma virus, a fraction of the cells is morphologically transformed. Transformation may be demonstrated in two ways: 1) When infected cells are grown on glass, dense colonies of transformed cells develop from the confluent monolayer of untransformed cells in which multiplication has stopped because of their contiguity. 2) In agar, colonies derived from transformed cells are larger and morphologically distinct from those formed by the untransformed cells. The variant cells produce tumors in hamsters. Their transplantability is increased by polyoma transformation. Transformed cells possess a new polyoma-specific cell antigen.