Gretchen L. Eiben

Loss of immunogenic epitopes by tumors has urged the development of vaccines against multiple epitopes. Recombinant DNA technologies have opened the possibility to develop multiepitope vaccines in a relatively rapid and efficient way. We have constructed four naked DNA-based multiepitope vaccines, containing CTL, Th cell, and B cell epitopes of the human papillomavirus type 16. Here we show that gene gun-mediated vaccination with an epitope-based DNA vaccine protects 100% of the vaccinated mice against a lethal tumor challenge. The addition of spacers between the epitopes was crucial for the epitope-induced tumor protection, as the same DNA construct without spacers was significantly less effective and only protected 50% of the mice. When tested for therapeutic potential, only the epitope construct with defined spacers significantly reduced the size of established tumors, but failed to induce tumor regression. Only after targeting the vaccine-encoded protein to the protein degradation pathway by linking it to ubiquitin, the vaccine-induced T cell-mediated eradication of 100% of 7-day established tumors in mice. The finding that defined flanking sequences around epitopes and protein targeting dramatically increased the efficacy of epitope string DNA vaccines against established tumors will be of importance for the further development of multiepitope DNA vaccines toward clinical application.

The etiological role of human papillomaviruses (HPV) in cervical and other cancers suggests that therapeutic vaccines directed against requisite viral antigens may eradicate tumors or their precursors. A Venezuelan equine encephalitis (VEE) alphavirus vector delivering the HPV16 E7 RNA was evaluated for antitumor efficacy using a murine E7+ tumor model. Vaccination with VEE replicon particles expressing E7 (E7-VRP) induced class I-restricted CD8+ T-cell responses as determined by IFN-gamma enzyme-linked immunospot (ELISPOT), tetramer, and cytotoxicity assays. E7-VRP vaccination prevented tumor development in all of the mice and effectively eliminated 7-day established tumors in 67% of tumor-bearing mice. The induction of protective T-cell responses was dependent on CD8+, but not CD4+ T cells. Long-lasting T-cell memory responses developed in E7-VRP-vaccinated mice as determined by complete protection from tumor challenge 3 months after the final vaccination. These promising results highlight the potent CD8+ T-cell-mediated antitumor effects elicited by VEE replicon-based vectors and support their further development toward clinical testing against cervical intraepithelial neoplasia or carcinoma.

Certain human cancers are linked to infection by oncogenic viruses that are able to cause transformation of the normal host cell into a cancerous cell. Human papillomavirus (HPV) DNA and expression of viral transforming proteins are found in virtually all cervical cancer cells, indicating an important role of this virus in the pathogenesis of the disease. Evidence exists that the immune response to cancer cells can play a major role in determining the outcome of disease. The fact that HPV is a necessary cause for cervical cancer provides a clear opportunity to develop a therapeutic vaccine against the virus to treat patients with cervical cancer at its early and late stages. Development of a prophylactic vaccine for HPV would also reduce the incidence of cervical neoplasias by preventing virus infection. Various candidate HPV vaccines are being developed and tested in animal models and/or in human clinical trials. These HPV vaccines, both preventive and therapeutic, are the subjects of this review.

Carcinomas of the anogenital tract, particularly cancer of the cervix, account for almost 12% of all cancers in women, and so represent the second most frequent gynecological malignancy in the world (48). It is well established that chronic infection of cervical epithelium by human papillomaviruses (HPV) is necessary for the development of cervical cancer. In fact, HPV DNA has been demonstrated in more than 99.7% of cervical cancer biopsy specimens, with high-risk HPV16 and HPV18 sequences being most prevalent (45,73). Therefore, an effective vaccine that would mount an immune response against HPV-related proteins might contribute to the prevention or elimination of HPV expressing lesions. This review will concentrate on the most recent advances in vaccine-mediated prevention and immunotherapy of HPV-induced cervical cancer, including presentations from the 20(th) International HPV Conference held in October 2002 in Paris.