Abstract
High-risk types of human papillomavirus (HPV) cause over 500,000 cervical, anogenital, and a subset of head and neck cancers cases per year. Owning to lack of efficacious treatment regimen currently, therapeutic HPV vaccine is an ideal option to control HPV-mediated maligancies. Although induction of cytotoxic T lymphocytes (CTLs) is important for therapeutic vaccination, the cancer-associated immunosuppressive milieu often impairs the efficacy of such therapies. Therefore, the simultaneous induction of tumor-specific CTLs and reversal of the immunosuppression is necessary for therapeutic vaccination. A recombinant lipidated immunogen (rlipo-E7m) containing an inactivated HPV16E7 (E7m) and a bacterial lipid moiety with toll-like receptor 2 (TLR2) agonist activity has been demonstrated possess robust anti-tumor activity through induction of CTL response. To enhance therapeutic effects, TLR9 agonist (unmethylated CpG oligodeoxynucleotide, CpG ODN) was admixed with rlipo-E7m to treat large tumor in a mouse model of HPV-associated cancer. We found that CpG ODN synergistically enhanced tumor-specific CTL responses in tumor-bearing mice and eradicates large tumors (6-8 mm in diameter) when combined with rlipo-E7m. In addition, the combinations dramatically inhibit local immunosuppressive cells (CD11b+Gr1+, CD11b+F4/80+ and CD4+CD25+FOXP3+) numbers and increase infiltrating CTLs number in tumors. Administration of suboptimal doses of chemotherapeutic agent with rlipo-E7m and CpG ODN increased the survival time of mice-bearing large tumor (＞10 mm in diameter). These findings suggest a novel therapeutic role for targeted injections of TLR2 agonist-fused tumor antigen and CpG ODN to direct CTL migration to the tumor bed and repress the immunosuppressive environment in tumor-bearing host. This promising approach could be applied for the development of additional therapeutic cancer vaccines.