Abstract
BACKGROUND
Hepatitis B virus (HBV)‐associated hepatocellular carcinoma (HCC) expresses hepatitis B surface antigen (HBsAg) on its cell surface, and this may serve as a tumor‐associated antigen. It was shown previously that adoptive transfer of immunity against HBsAg facilitates the suppression of experimental human HCC‐expressing HBsAg in athymic mice. The authors recently showed that it was possible to augment the anti‐HBV immune response through induction of oral immune regulation for HBV‐associated antigens. The objective of this study was to evaluate the effect of oral immune regulation for HBV antigens on the growth of HBsAg‐expressing HCC.
METHODS
Recipient athymic Balb/c mice were irradiated sublethally and injected with 107 human hepatoma cells followed by the adoptive transfer of 2 × 106 splenocytes from donor mice. Four groups of donor Balb/c mice were studied: Two groups were immune modulated through oral administration of HBV antigens (HBsAg, PreS1, and Pre S2) or bovine serum albumin (BSA). Two control groups were immunized for HBsAg and fed HBV antigens or BSA. Recipient mice were followed for tumor volume and serum α‐fetoprotein (αFP) levels. The humoral immune response was determined by measuring serum HBs antibodies. HBV specific T‐cell immune modulation was assessed in vitro by HBV specific T‐cell proliferation and interferon γ (IFNγ) ELISPOT assays as well as cytokine expression by reverse transcriptase‐polymerse chain reaction assays.
RESULTS
The adoptive transfer of orally immune modulated HBV splenocytes induced complete tumor suppression in recipient mice compared with control mice transplanted with nonimmune modulated cells (BSA), which showed significant tumor growth (serum αFP levels were 3.5 ng/mL and 2320.0 ng/mL, respectively). Control mice transplanted with anti‐HBs immunized cells (with or without oral immune modulation) manifested similar tumor suppression (3.5 ng/mL and 0.5 ng/mL, respectively). Immunoregulation for HBV antigens augmented the HBV specific T‐cell immune response, as manifested by an increase in HBV specific T‐cell proliferation and IFNγ ELISPOT assays in mice orally immune regulated with HBV proteins compared with naïve mice. Tumor suppression was mediated through increased IFNγ production in immune regulated and immunized mice.
CONCLUSIONS
The induction of oral immune regulation for HBV antigens modulated the antitumor immune response, thus suppressing the growth of HCC in mice. This effect was mediated by the enhancement of anti‐HBV specific T‐cell immunity. Cancer 2002;94:406–14. © 2002 American Cancer Society.