OBJECTIVE: To test whether an E7 peptide/CpG vaccine is effective in preventing and treating human papillomavirus-positive tumors in a murine model. INTERVENTION: First, an E7 peptide/CpG vaccine was administered systemically on days -14 and -7, and tumor cells were injected subcutaneously on day 0. Second, tumor cells were injected on day 0, and vaccine was administered on days 7, 14, and 21. MAIN OUTCOME MEASURES: Tumor size was measured 3 times per week. A tetramer assay was used to assess the presence of activated, E7-specific lymphocytes in spleen and tumor cells harvested from mice treated with a similar vaccination regimen. RESULTS: In the prophylactic study, 75% of mice injected with E7 peptide/CpG resisted tumor formation. In the therapeutic setting, tumors initially regressed and experienced delayed progression when compared with controls. Survival rates improved in E7/CpG-vaccinated mice. Tetramer analysis detected increased numbers of activated, E7-specific lymphocytes in the spleens and tumors of animals treated with the experimental vaccine when compared with controls. CONCLUSION: The use of CpG motifs as an adjunct to peptide-based immunotherapy has potential impact on the treatment of human papillomavirus-associated cancers.