Studies on the transformation of human fetal cell cultures by simian virus 40

A human fetal fibroblast strain, belonging to a group resistant to SV40 transformation, was transformed by SV40 through a multiple inoculation procedure. Two independently transformed cells were described in comparison with each other. The proportions of cells with the nuclei possessing V antigen were 2.9% at the 5th passage in one strain and 1.1 % at the 4th passage in another, and they declined gradually as frequent passages were repeated. The percentages of the transformed cells with V antigen-positive nuclei were, in both strains, quantitatively compatible with those of the cells with the nuclei full of virus particles in crystalline arrays, which were demonstrated by immunofluorescent studies and electron microscopy.