Detection of a small virus in a cultivated human Wilms' tumor

After 15 months of in vitro cultivation and after “spontaneous transformation” from a fibroblastoid to epithelioid morphological appearance, a human Wilms' tumor culture was shown by electron microscopy to contain a small virus. The virus measures 45-50 mμ in diameter, contains an electron-dense nucleoid, and is surrounded by a closely adherent double-membrane. Thus, morphologically, it resembles papova viruses. Attempts to establish in vitro and in vivo activity of the virus, thus far, have been unsuccessful. Viral replication has been demonstrated only by electron microscopy in the cultivated cells where virus was first detected. Attempts are continuing to establish a biological assay for the virus and to recover similar agents from other Wilms' tumors.