Changes in HLA A, B, C expression during "spontaneous" transformation of human urothelial cells in vivo.

The immortalized but non-tumourigenic and non-invasive human urothelial cell line, Hu 609, known to express the appropriate HLA A,B antigens (A2,-; B5,-) has previously been demonstrated to undergo "spontaneous" in vitro transformation into an invasive and tumourigenic subline, Hu 609T/MV. This subline does not express the polymorphic HLA epitopes. In the present investigation we have followed two additional "spontaneous" transformations of the Hu 609 cell line into malignant sublines. Evidence is presented that the development of morphological changes and tumourigenicity were accompanied by a gradual loss of the expression of polymorphic HLA A,B epitopes and a reduction in the expression of monomorphic HLA A,B,C antigens. Antigens could be detected again after neuraminidase treatment. We conclude that the urothelial Hu 609 cell line after "spontaneous" transformation still possesses the HLA A,B epitopes. The observed quantitative differences in HLA expression between Hu 609 and its malignant sublines may be due to masking of the HLA antigens by sialic acid containing tumour-associated highly branched glycoproteins.