Human herpesvirus-6: tumorigenicity and tumor infiltrating lymphocytes

We previously reported that human herpes-virus-6 (HHV-6) genome (strain GS) and a cloned subfragment (pZVH14) transfected NIH 3T3 cells, induced foci of transformation with a frequency significantly above the background level. The transformed cells produced tumors in nude mice and immunocompetent (Swiss) mice. In the current study, nude mice tumors were passed into Swiss mice and more aggressive tumors (G-2TS and 14-2TS derived from HHV-6 genome and pZVH14 DNA, respectively) were produced. 14-2TS tumors caused lung metastasis upon intravenous injection. In the case of subcutaneously growing aggressive tumors, tumor infiltrating lymphocytes (TIL) were isolated and characterized as T cells but lacked tumor specific killing as monitored by 51Cr-release assays. TIL lost activity at day 52 in a 4 h assay (but not in a 19 h assay) against the autologous tumor, but not a Maloney virus induced tumor (Yac-1). These studies indicate that an established nontumorigenic fibroblast cell line, when transfected with pZVH14 DNA of HHV-6, acquires both tumorigenic and metastatic potential and tumor bearing hosts mount immune response against such tumors.