Ultrastructural differentiation in the nude mouse of transformed cells isolated from the human fetal pituitary gland

Spontaneously transformed human fetal pituitary cells were isolated from first-passage cultures after 3 to 6 months of long-term maintenance in growth medium containing 15% fetal calf serum. The cells, when injected into nude mice, developed into large tumors in 1 to 2 weeks. Attempts to detect growth hormone, prolactin, follicle-stimulating hormone, luteinizing hormone, or thyroid-stimulating hormone from nude mouse plasma and tumor homogenate by radioimmunoassay were unsuccessful. These hormones could not be demonstrated in tumor cell cytoplasm by immunocytochemistry. Two human fetal pituitary (HFP) cell strains (HFP-T2, HFP-F4) from tissue culture examined at the electron microscopic level were undifferentiated by ultrastructural criteria. However, tumor cells in the nude mice showed signs of fine structural differentiation with well-developed rough endoplasmic reticulum profiles, secretory granules, and intercellular junctions. The tumor cells lost the features of morphological differentiation when returned to tissue culture. These changes could be repeated by alternate passage in nude mouse and tissue culture.