Interleukin (IL)-12 has been reported to induce cellular immune responses for protection against tumor formation. Here we investigate the utility of adenoviral delivery of IL-12 as an adjuvant for a human papillomavirus E7 subunit vaccine in a mouse tumor challenge model. Direct intratumoral injection of AdIL-12 resulted in a significant suppression of tumor growth compared to the control group. Injection of E7 protein into either a tumor site or the distance site along with AdIL-12 further enhanced antitumor effects significantly higher than either AdIL-12 or E7 injection alone. This combined injection resulted in complete regression of 9-mm-sized tumor in 40% of animals as well as lasting antitumor immunity against tumor recurrence. We also evaluated immune responses induced by these injections. AdIL-12 plus E7 enhanced E7-specific antibody responses significantly higher than AdIL-12 or E7 injection. In particular, the production level of interferon (IFN)-gamma from E7-specific CD4(+) T cells was similar between AdIL-12 group and AdIL-12 + E7 group. However, IFN-gamma production from E7-specific CD8(+) T cells was the most significant when injected with AdIL-12 + E7. This was consistent with intracellular IFN-gamma staining levels of CD8(+) T cells, suggesting that AdIL-12 + E7 injection enhances antitumor immunity in the human papillomavirus (HPV) 16 tumor model through increased expansion of the cytotoxic T-lymphocyte (CTL) subset. This enhanced protection appeared to be mediated by CD8(+) T cells, as determined by in vivo T-cell subset deletion. Thus, these studies demonstrate that E7 vaccines can induce CTL responses responsible for antitumor effects in the presence of IL-12 delivered via adenovirus vectors. This likely provides one additional approach for immune therapy against cervical cancers.