DNA Vaccines against Infectious Diseases and Cancer

DNA vaccines, electroporation and their applications in cancer treatment

Numerous animal studies and recent clinical studies have shown that electroporation-delivered DNA vaccines can elicit robust Ag-specific CTL responses and reduce disease severity. However, cancer antigens are generally poorly immunogenic, requiring special conditions for immune response induction. To date, many different approaches have been used to elicit Ag-specific CTL and anti-neoplastic responses to DNA vaccines against cancer. In vivo electroporation is one example, whereas others include DNA manipulation, xenogeneic antigen use, immune stimulatory molecule and immune response regulator application, DNA prime-boost immunization strategy use and different DNA delivery methods. These strategies likely increase the immunogenicity of cancer DNA vaccines, thereby contributing to cancer eradication. However, cancer cells are heterogeneous and might become CTL-resistant. Thus, understanding the CTL resistance mechanism(s) employed by cancer cells is critical to develop counter-measures for this immune escape. In this review, the use of electroporation as a DNA delivery method, the strategies used to enhance the immune responses, the cancer antigens that have been tested, and the escape mechanism(s) used by tumor cells are discussed, with a focus on the progress of clinical trials using cancer DNA vaccines.

Antitumor therapeutic and antimetastatic activity of electroporation-delivered human papillomavirus 16 E7 DNA vaccines: a possible mechanism for enhanced tumor control

DNA vaccines are known to be lacking in immunogenicity in humans. Presently, electroporation (EP) is thought to overcome this limitation. Here, we investigate whether human papillomavirus 16 E7 DNA vaccines delivered by EP might elicit potent antitumor activity in animal cervical cancer models, with a focus on the underlying mechanism(s). Intramuscular (IM)-EP delivery of E7 DNA vaccines induced more potent antitumor therapeutic and antimetastatic activity compared with IM delivery. Moreover, the tumor-controlled animals by IM-EP possessed long-term memory responses to parental tumor cells. This improved antitumor effect was concomitant with augmented Ag-specific CTL activities. IM-EP also induced IgG and Th-cell responses higher than IM delivery. Finally, IM-EP resulted in more antigen production in and more attraction of immune cells into the site of DNA injection, suggesting that these biological and immunological changes made by IM-EP might be responsible for enhanced CTL activities and antitumor resistance. Thus, this study shows that IM-EP can induce more potent antitumor activity by augmenting CTL responses possibly through more antigen production in and more attraction of immune cells into the muscle sites. This study also suggests that IM-EP of E7 DNA vaccines might be a potential approach toward treating patients with cervical cancer.