The human hepatoma cell line, PLC/PRF/5, which is persistently infected with hepatitis B virus (HBV), has integrated HBV-DNA, secretes HBV surface antigen (HBsAg), and does not grow readily in congenitally athymic (nu/nu) mice. The present investigation was undertaken to ascertain whether the low tumorigenicity of this cell line was governed by a host immune response and/or was related to expression of HBsAg. Subcutaneous injection of 4-5 X 106 cells into BALB/c nude mice produced localized encapsulated tumors with morphologic features of primary hepatocellular carcinoma in 25% of the animals within 29-40 d. No tumor growth was observed at lower cell inocula. In contrast, SK-HEP-1, an HBV-negative human hepatoma cell line, produced tumors at 1-5 X 106 cells inocula in 66% of the animals. Immunosuppression of mice with antilymphocyte serum (ALS) or irradiation increased tumor incidence in mice inoculated with 1 X 106 PLC/PRF/5 cells to almost 100% and produced local invasiveness. Immunosuppression also reduced the latency, i.e., time to tumor appearance, and increased mean tumor weight. These results suggest that tumorigenicity was limited by the host immune response.
Daniel Shouval, Bracha Rager-Zisman, Phuc Quan, David A. Shafritz, Barry R. Bloom, Lola M. Reid