HER2/neu-specific Breast Cancer Vaccine

Breast cancer is the most common cancer among women. Of all breast cancers cases, approximately 30 percent have amplification of the self-antigen HER2/neu. Later studies demonstrated that HER2/neu-specific antibody and T cell responses were found in HER2/neu-positive breast cancer patients, indicating HER2/neu is a good target for active immunotherapy. A humanized anti HER2/neu antibody trastuzumab, was developed and found to be an effective therapy for HER2/neu. However, acquired antibody resistance occurs sooner or later in antibody treated patients. Such limitations of antibody therapy provoked scientists into the search for other therapeutic strategies. HER2/neu-targeted immunotherapeutic strategies, including vaccines using tumor lysates, protein/peptide, DNA, adenoviral vectors (AdV) and dendritic cells (DCs) pulsed with the above reagents, have been shown to be effective in experimental models. However, they have also been proven to be incapable of breaking tolerance towards HER2/neu in clinical trials and eliciting then have not elicited adequate antitumor immunity in curing HER2/neu positive breast cancer in transgenic mice with HER2/neu-specific immune tolerance, although both humoral and cellular immune responses could be detected. CD4+ helper T (Th) cells play crucial roles in priming, expansion and memory of both humoral and CD8+ cytotoxic T lymphocyte (CTL) responses. Therefore, they are essential in antitumor immunity. The tetanus toxoid Th epitope 947-967 P30, FNNFTVSFWLRVPKVSASHLE, has been found to be a universal epitope in sensitizing and proliferating CD4+ T cells ex vivo. OVA-P30 peptide vaccine could break CD8+ and CD4+ T cell tolerances against the neo-self-antigen OVA; it was able to protect transgenic rat insulin promoter (RIP)-mOVA mice from tumor growth. Adenovirus-based vaccines are able to induce high frequencies of transgene product-specific CD8+ T cell responses. In this study, we immunized C57BL/6 mice with OVA-expressing AdVOVA. We found that AdVOVA induced sustained OVA-specific CTL responses, leading to preventive antitumor immunity against OVA-expressing BL6-10OVA tumor cell challenge in wild-type C57BL/6 mice. In addition, we also immunized transgenic FVBneuN mice with neu-expressing AdVneu. We found that AdVneu vaccination induced neu-specific CTL responses, leading to partial reduction of breast carcinogenesis in FVBneuN mice. To assess whether the foreign Th epitope P30 enhances CD4+ and CD8+ T cell responses, we constructed another two recombinant AdVs (AdVOVA-P30 and AdVneu-P30), expressing OVA-P30 and HER2/neu-P30 gene, respectively. We transfected C57BL/6 mouse bone marrow dendritic cells (DCs) with AdVOVA and AdVOVA-P30 for preparation of DCOVA and DCOVA-P30 vaccines. We immunized C57BL/6 mice with DCOVA and DCOVA-P30 and then assessed CD4+ and CD8+ T cell responses and antitumor immunity subsequent to immunization. We demonstrated that both DCOVA and DCOVA-P30 were capable of stimulating both enhanced CD4+ and CD8+ T cell responses, leading to preventive antitumor immunity against challenge of OVA-expressing BL6-10OVA tumor in 100% (8/8) of the immunized mice. However, DCOVA-P30 induced more efficient CD4+ and CD8+ T cell responses than DCOVA, leading to significant reduction of growth of 3 day-established lung tumor metastasis in C57BL/6 mice, indicating that the foreign CD4+ Th epitope P30 can enhance both CD4+ and CD8+ T cell responses. In this study, we also transfected transgenic FVBneuN mouse bone marrow DCs with AdVneu and AdVneu-P30 for preparation of DCneu and DCneu-P30 vaccines. We immunized transgenic FVBneuN mice with DCneu and DCneu-P30 and then assessed CD4+ and CD8+ T cell responses and antitumor immunity subsequent to immunization. We demonstrated that DCneu-P30 but not DCneu was capable of stimulating both enhanced CD4+ and CD8+ T cell responses, leading to preventive antitumor immunity against challenge with 0.3×106 neu-expressing Tg1-1 tumor cells in 100% (8/8) immunized transgenic FVBneuN mice; this significantly reduced lung metastasis tumor colonies in immunized transgenic FVBneuN mice challenged with 1×106 Tg1-1 tumor cells, confirming that incooperation of foreign CD4+ Th epitope P30 into DC-based vaccines can at least partially break self-immune tolerance, leading to enhanced CTL responses and antitumor immunity in transgenic FVBneuN mice. Taken together, our data demonstrate that the CD4+ Th epitope P30 can enhance both CD4+ and CD8+ T cell responses, leading to enhanced DC-stimulated antitumor immunity. This may have impact in designing new DC-based vaccines for treatment of breast cancer and other types of human malignancies