| Abstract: | From a single primary culture of pooled hamster embryos, two morphologically distinct, malignant cell lines have evolved in the absence of experimentally applied selective factors, chemical, physical or viral. The cells of both sublines are male. One subline, designated Nil-1, is extremely pleomorphic with lobulated nuclei and micronuclei. It was tumorigenic at the 35th passage (18 weeks) after initiation of the primary culture. The second subline, designated Nil-2, is fibroblastic and required 30–45 more subcultures than Nil-1 to become tumorigenic. The malignant properties of Nil-1 and Nil-2 were not correlated with any specific chromosome changes. At a time when Nil-2 cells were still sensitive to contact inhibition and were not tumorigenic, they could be transformed by polyoma virus but not by SV40. The parent primary culture, however, was susceptible to transformation by SV40. Neither subline contained SV5 or lymphocytic choriomeningitis viral antigen or specific complement fixing antigen induced by polyoma virus, SV40, Rous sarcoma virus or adenovirus types 7, 12, 18, 21, or 31. No cytopathogenic agent and no mycoplasma could be isolated from the parent culture or sublires; no new transplantation antigen could be demonstrated. The possibilities in the etiology of the transformation are discussed. |
