ABSTRACT
ANTIGEN DELIVERY SYSTEMS AND ROUTE The first report demonstrating the effectiveness of heterologous prime-boost immunization strategies used a recombinant influenza virus expressing a malarial antigen as a priming agent and a recombinant vaccinia virus expressing the same antigen as the boost (6). Subsequently it was found that, surprisingly, nonreplicating vectors could induce comparable or stronger cellular immune responses than these replicating viruses (7). Since this early work, many different antigen delivery systems have been evaluated in heterologous prime-boost regimens. Plasmid DNA, recombinant protein combined with adjuvant, and recombinant viral and bacterial vectors are among those most commonly used. However, while all of these vectors can prime an immune response, some are more effective than others at boosting. In particular, recombinant viral vectors, including both poxviral vectors such as modified virus Ankara (MVA) and adenoviral vectors have been found to be extremely effective at boosting previously primed cellular immune responses (12-14). Further discussion on the individual viral vectors can be found elsewhere in this volume.
