To investigate the biological characterization and antitumor activities of GM-CSF gene-transfected dendritic cells, the splenic dendritic cells were infected with GM-CSF recombinant replication-deficient adenovirusesin vitro. Their enhanced expression of B7 was demonstrated by FACS analysis, and more potent stimulatory activity was confirmed by allogeneic MLR. Immunization of dendritic cells pulsed with irradiated B16 melanoma cells induced significant CTL and enabled host to resist the challenge of wild-type B16 cells. When they were transfected with GM-CSF gene subsequently, the induced CTL activity was higher, and the produced protection against B16 cell challenge and therapeutic effect on the mice with preestablished pulmonary metastases more effective. These data suggest that the dendritic cells pulsed with tumor antigen then transfected with GM-CSF gene can be used as an effective vaccine in tumor immunotherapy.