AIM: To observe biological characteristics of hepatocarcinoma cells before and after CD80 transfection and to compare the effect of CD80-transfected hepatocarcinoma cells on T lymphocyte activation. METHODS: Retro virus vector carrying CD80 gene was transfected into HepG2 cells to establish CD80-transfected hepatocarcinoma cells (HepG2/hCD80). Flow cytometry (FCM) was performed to detect CD80 expression in the transfected cells. RT-PCR was used to evaluate CD80 expression at mRNA level. In the presence of anti-CD3 mAb, the proliferation of T lymphocyte was observed by MTT. Meanwhile, the expression of activated molecule marker CD25 was analyzed through FCM.RESULTS: A stable cell line HepG2/hCD80 expressing the human CD80 was established. Growth curve showed that the molecule CD80 could obviously decrease the growth of tumor cells. HepG2/hCD80 was evidenced to have a potency to enhance T cell proliferation and upregulate CD25 expression.CONCLUSION: CD80 transfection can lower malignant phenotype of hepatocarcinoma cells. CD80transfection has a down-regulatory effect to activated T cells in vitro.