Establishment of eighteen clones of Ishikawa cells.

Ishikawa cells, which derive from a well differentiated human endometrial adenocarcinoma, were cloned using the limiting dilution method in an attempt to preserve well differentiated cells. Eighteen clones were obtained. According to their morphologic characteristics, there were six well differentiated, seven moderately differentiated, three poorly differentiated and two adenosquamous carcinoma clones. All of them were transplantable into node mice. Fifteen of the 17 clones were positive for estrogen receptors and all of the clones examined were positive for progesterone receptors. There were no significant differences in terms of population doubling time, plating efficiency or saturation density among these clones. On the basis of these results, we concluded that Ishikawa cells are not as homogeneous morphologically as we thought, since cells with varying degrees of differentiation have already mingled with the parent cell line. It is verified that the adenosquamous cell carcinoma of the endometrium can arise from one stem cell. It would be impossible to revive the cultured cells after having undergone their changes to the original conditions. Therefore, to preserve the characteristics of an established cell line, the cells should be frozen at a very early stage. It is also important to avoid frequent passages when special characters of the cells are necessary for a given investigation.