Trisomy 7 has been found as the sole clonal chromosome aberration in a number of tumor types, including renal cell carcinomas (RCC), and also in non-neoplastic kidney tissue. It has recently been proposed that the cells harboring trisomy 7 in RCC and in the surrounding tissue may be tumor infiltrating T-helper lymphocytes. We performed cytogenetic analysis of metaphase cells and FISH of interphase nuclei in uncultured and cultured non-neoplastic kidney tissues from 13 patients with renal or urothelial carcinomas, and 4 patients with inflammatory kidney diseases. FISH analysis showed that the frequency of +7 varied between 1.0–8.9% (mean 3.3%) in uncultured cells and between 0.4–8.6 % (mean 4.4%) after one week of cell culture. The frequency of +7 after one week of culture was 1.0–19.0% (mean 6.1%) as determined by cytogenetic analysis. Immunoenzymatic staining of both uncultured and cultured cells with the alkaline phosphatase reaction and monoclonal antibodies for CD3 showed that the frequency of T-cells in uncultured cells and in primary cultures varied between 2.9–10%. The number of T-cells decreased with time and number of in vitro passages to less than 1 % after 7–8 weeks, but the frequency of +7 remained fairly constant. Combination of FISH with immunostaining using CD3 for T-lymphocytes and cytokeratins for epithelial cells showed that the cells with +7 were mainly epithelial cells whereas only 0–5 % were T-lymphocytes. The results have obvious implications for the interpretation of the significance of trisomy 7 i
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