To investigate the function of B7 co-stimulator in activation and differentiation of T cell, B7 gene was transfected into Raji and Jurkat cells by liposome, B7 expression in tumor cells was detected with flow cytometry, and expression of IL-2, IL-4 and IFN-gammamRNA was detected by RT-PCR. Kinetics of secretion of three cytokines was also analyzed at 4, 12, 20 and 48 hours after gene transfection. The results showed that B7(+) Raji cells could induce mRNA expression of IL-2, IL-4 and IFN-gamma on T cell surface; B7(+) Jurkat cells could induce secretion of IL-2 and IFN-gamma. However, B7(-) Raji and B7(-) Jurkat cells could not induce secretion of cytokines. Kinetics of the three cytokines secretion were different, IL-2 and IL-4 were only detectable after 4 hours of T cell activation, whereas IFN-c was detectable after 12 hours of stimulation. The peak levels of IL-2, IL-4 and IFN-gamma were found at 20 hours after activation. It was concluded that tumor cell lines transfected with B7 gene could enhance their immunocompetence, activating T cell efficiently and B7-1 play more critical role in T cell activation and differentiation.