Fetal isoenzyme expression of heterotransplanted HeLa cells in nude mice.

The nude mouse has been successfully employed for the propagation of human tumors, without the need for immunosuppression. In light of the limited data on embryonic gene expression in such tumors, we undertook a study of fetal isoenzyme expression during tumor growth. HeLa TCRC-1 which has been shown to produce the placental Regan isoenzyme was used in these studies. The isoenzyme produced by these cells in culture is initially replaced by an isoenzyme referred to as chorionic. In the later stages of tumor growth, the so-called oncoamniotic (FL) isoenzyme then becomes the dominant enzyme form. The chorionic isoenzyme is produced by the early chorionic membranes of the developing conceptus, while the oncoamniotic (FL) isoenzyme is most similar to that found in the fetal human intestine. The alteration in the expression of fetal isoenzymes in tumors growing in the nude mouse is similar to that seen in the immunosuppressed rat and hamster host animals, indicating that the phenomenon is not related to immunosuppression per se.