OBJECTIVETo investigate the effect of adenovirus vector encoding human vascular endothelial growth factor receptor-2 (hVEGFR-2 or hKDR) on breaking the immune tolerance and inducing immunity against murine hepatocellular carcinomas.

METHODSHuman and mouse KDR cDNA were cloned from human umbilical vein endothelial cells (HUVEC) and C57BL/6 mouse embryo cells respectively using RT-PCR, and then Ad hKDR and Ad mKDR were constructed. Seven days after immunization of the mice with Ad hKDR or Ad mKDR, an analysis of cytotoxic activity of antigen-specific cytotoxic T lymphocytes (CTL) was made by lactate dehydrogenase (LDH) release assay, in which splenocytes of the immunized mice acted as effectors and Hepa 1-6/mKDR cells as the targets. In addition, the survival of the mice immunized with Hepa 1-6 hepatoma cells was checked.

RESULTSSeven days after immunization, the 6 h killing activities of CTL elicited by the Ad hKDR were 84.3%+/-6.7%, 71.5%+/-5.2%, and 44.6%+/-4.7% at the ratio of the effectors:targets (E:T) of 100:1, 50:1, and 25:1, respectively. Correspondingly, the CTL activities by Ad mKDR were 65.2%+/-6.1%, 46.7%+/-5.0%, and 22.6%+/-3.7%. Sixty percent of the Ad hKDR-immunized mice with 5*10(6) Hepa 1-6 hepatoma cells were still alive two months after the inoculation, whereas just 40% of the Ad mKDR-immunized mice with 2*10(6) Hepa 1-6 cells survived two months. When CD8+ or CD4+ T lymphocytes were deleted in the mice the above mentioned CTL activities and protection of the mice from tumors disappeared.

CONCLUSIONAdenovirus vector-mediated xenogeneic KDR can effectively break the immune tolerance to hepatocellular carcinomas in an animal model and induce a strong antigen-specific T cell response, which is dependent on CD8+ and CD4+ T cells.