Induction of brain tumors in hamsters with BK virus, a human papovavirus

The oncogenicity of BK virus for the central nervous system was studied in newborn hamsters. The virus was weakly oncogenic after intracerebral inoculation. Two of 45 hamsters treated with antithymocyte serum developed tumors whereas no untreated hamsters developed tumors. Both tumors were choroid plexus papillomas by histologic and electron microscopic examination. Cells cultured from one tumor had growth characteristics of transformed cells and had intranuclear T antigen; but infectious virus could not be rescued. Cultured tumor cells were weakly oncogenic for hamsters, but theoncogenicity of these cells was enhanced when the recipient animals were treated with antithymocyte serum. The possible role of host immune response as a basis for the weak oncogenicity of BK virus is discussed.