A classification of human urothelial cells propagated in vitro.

Human urothelial cell lines of non-malignant and malignant origin were classified into three grades of transformation, i.e. TGr I, TGr II, and TGr III, which differ from primary and early cultures of normal bladder mucosa (TGr 0) by growth in the absence of fibroblasts, prolonged survival, increasing chromosomal abnormalities, and antigenic modifications. Non-malignant pure epithelial cell lines with a prolonged, but finite life span (18-38 passager in vitro) were classified as TGr I. These cells were characterized by chromosomal counts showing a considerable variation but with a near-diploid mode and a smaller size but otherwise normal morphology. TGr II cells differed from TGr I by infinite growth transformation and wide morphological variability. TGr III cells were above all characterized by their ability to produce tumors in nude mice and to invade and destroy fragments of embryonic heart in vitro. These immortalized cells were small with a large nucleus and a uniform polygonal shape. Chromosomal counts showed pronounced aneuploidy with an increased number of chromosomes.