Objective To investigate CD80 expression on human tumor cell lines and establish stable CD80 expression transfectants to illustrate CD80 costimulation on the T cell proliferation and cytokine production.Methods Raji, MDA-453, MCF-7, Hela, 3AO, MKN-45 and EBV transformed B cell were detected for CD80 expression by RT-PCR. CD80 cDNA subcloned to retrovirus vector pLXSN, with them stable CD80 transfectanants were established. With specific mAb BB1 and FACS assay, the expression of CD80 were detected. Anti-CD3 induced T lymphocyte proliferation and IL-2, IFN-r production were performed to evaluate CD80 costimulatory activity in the presence of calcium ionophore A23187 and phorbol ester PMA.Results CD80 (B7-1) expression of MDA-453, MCF-7, Hela, 3AO, MKN-45 was negative, and that of Raji and EBV transformed B cell was positive by RT-PCR and FACS methods. Cocultured with CD80 transfected human breast carcinoma cell line MDA-453, anti-CD3 induced T cells proliferation and cytokine production were significantly increased in the presence of A23187 and PMA, but not with parental MDA-453.Conclusions CD80 expression is absent on most human tumor cell line except for Raji and EBV transformed B cell. Full activation of T cell needs CD80 costimulation. Influence of CD80costimulation on cytokine production is mainly regulated via IL-2 and IFN-r.