BK virus T antigens induce kidney carcinomas and thymoproliferative disorders in transgenic mice

Renal adenocarcinomas and/or extremely enlarged thymuses (up to 250 times normal size) were observed in 60 of 78 mice in a transgenic line containing a single copy of the BK virus (BKV) early region. Enlarged thymuses from different mice displayed thymoproliferative disorders of varying severity, ranging from extreme hyperplasia to thymomas and lymphomas. All kidney tumor DNAs analyzed contained highly amplified BKV sequences with multiple rearrangements in cellular DNA flanking the transgene, whereas amplification and rearrangement were observed only in some enlarged thymus DNAs. Expression of BKV T antigens was restricted to epithelial cells of kidney tumors and enlarged thymuses and was not detected in any normal tissues. Although thymocytes proliferated to numbers much greater than normal in the enlarged thymuses, no T antigen expression was detected in thymocytes.