CpG ODN enhances the protective effect of Id/GM-CSF. Mice were immunized with a single injection of Id/GM-CSF and/or CpG ODN and challenged with tumor 3 days later. Survival was followed for 100 days. All mice that were alive after 51 days remained tumor-free for the entire observation period. Twenty mice were included in each group. (▪) No immunization; (▴) CpG ODN; (×) Id/GM-CSF; (•) Id/GM-CSF + CpG ODN.