Cancer immunotherapy using a DNA vaccine encoding the translocation domain of a bacterial toxin linked to a tumor antigen

Certain domains of bacterial toxins have been shown to facilitate translocation from extracellular and vesicular compartments into the cytoplasm. This feature represents an opportunity to enhance class I presentation of exogenous antigen to CD8⁺ T cells. We investigated this notion by creating a novel fusion of the translocation domain (domain II) of Pseudomonas aeruginosa exotoxin A (ETA(dII)) with a model tumor antigen, human papillomavirus type 16 E7, in the context of a DNA vaccine. Our in vitro studies indicated that cells transfected with ETA-(dII)/E7 DNA or dendritic cells pulsed with lysates containing ETA-(dII)/E7 protein exhibited enhanced MHC class I presentation of E7 antigen. Vaccination of mice with ETA(dII)/E7 DNA generated a dramatic increase in the number of ET-specific CD8⁺ T cell precursors (∼30-fold compared with wild-type E7 DNA) and converted a less effective DNA vaccine into one with significant potency against human papillomavirus type 16 E7-expressing murine tumors via a CD8-dependent pathway. These results indicate that fusion of the translocation domain of a bacterial toxin to an antigen may greatly enhance vaccine potency.