Isolation in newborn mice of tumour cell variants from a polyoma-transformed non-malignant cell line

Tumours developed in a proportion of newborn C 3H/Bi and F 1 C 3H/Bi × C 57BL hybrid mice inoculated with a polyoma virus-induced tumour cell line, non-tumourigenic in adult syngeneic mice. Some of the tumours were transplantable into adult mice, others were not. Tissue culture cell lines isolated from the transplantable and non-transplantable tumours differed in their tumourigenicity for adult mice and in their immunological properties. The relevance of these findings to tumour progression is discussed.