We have cultured cells from normal and benign mastopathy tissues under
conditions favoring epithelial cell proliferation. However, such prim
ary cells rapidly lose their ability to grow in vitro. Immortal lines
were established after transfection with SV 40 T gene and several cell
clones isolated from Normal Breast Adjacent to a tumor (NBAT 32 72 to
77) and two benign mastopathies (NPM 21 T1 to T14 and NPM 14 T4). Thi
s immortalization of epithelial cells reduced the doubling time of cul
tured cells and increased the densities of the cultured cell populatio
ns. Among there cell lines we have characterized five clones and found
differences in a number of aspects. Southern blot analysis showed tha
t the SV 40 T gene was stably integrated in the genome of all the esta
blished cell lines. Two of the clones (NPM 21 T2 and NPM 21 T4) were n
early diploid showing a high degree of stability. Two other clones (NP
M 14 T4 and NPM 21 T1) had near-tetraploid karyotypes, although quite
heterogeneous. Comparison of the ultrastructural phenotypes shows that
the two near-diploid cell lines were more differentiated than the two
others. Estradiol receptors measured by Scatchard analysis and by tra
nsactivation of vitellogenin promotor were absent from all the cell li
nes. Progesterone receptors measured by Scatchard analysis of hormone
binding were present in the NPM 14 T4 and NBAT 32 T4 cell lines. The N
PM 21 T1 cell line did not contain such steroid receptors. These cell
lines are persistent in long-term culture, thus providing a useful in
vitro model system for studying factors involved in the proliferation
and the transformation of human mammary epithelial cells.