Enhancing DNA vaccine potency by combining a strategy to prolong dendritic cell life with intracellular targeting strategies

We have recently shown that intradermal coadministration of DNA encoding Ag with DNA encoding inhibitors of apoptosis, including Bcl-x_L, prolongs dendritic cell (DC) life and thereby enhances the potency of DNA vaccines in vivo. We have also demonstrated that DNA vaccines targeting Ag to subcellular compartments, using proteins such as Mycobacterium tuberculosis heat shock protein 70, calreticulin, or the sorting signal of the lysosome-associated membrane protein type 1 (LAMP-1), enhanced DNA vaccine potency. In this study, we reasoned that the combination of a strategy to prolong DC life with intracellular targeting strategies might produce a more effective DNA vaccine against human papillomavirus E7. We showed that coadministration of DNA encoding Bcl-x_L with DNA encoding E7/heat shock protein 70, calreticulin/E7, or Sig/E7/LAMP-1 resulted in further enhancement of the E7-specific CD8⁺ T cell response for all three constructs. Of these strategies, mice vaccinated with Sig/E7/LAMP-1 DNA mixed with Bcl-x_L DNA showed the greatest increase in E7-specific CD8 ⁺ T cells (∼13-fold increase). This combination of strategies resulted in increased CD8⁺ T cell functional avidity, an increased E7-specific CD4⁺ Th1 cell response, enhanced tumor treatment ability, and stronger long-term tumor protection when compared with mice vaccinated without Bcl-x_LDNA. Therefore, DNA vaccines that combine strategies to enhance intracellular Ag processing and prolong DC life have potential clinical implications for control of viral infection and neoplasia.