Adenoviral-Vector-Mediated Gene Transfer to Dendritic Cells

Dendritic cells (DC) are the most potent antigen presenting cells capable of initiating T-cell-dependent immune responses (1 -5 ). This biologic potential can be harnessed to elicit effective antigen-specific immune responses by transferring the relevant antigens to the DC. Once the DC have been mobilized and purified, the relevant antigens can be transferred to the DC as intact proteins, or as peptides representing specific epitopes, or with gene transfer using sequences of DNA or RNA coding for the pertinent antigen(s) (6 -15 ). Theoretically, genetically modifying DC with genes coding for specific antigens has potential advantages over pulsing the DC with peptides repeating the antigen or antigen fragment. First, the genetically modified DC may present previously unknown epitopes in association with different MHC molecules. Second, gene transfer to DC ensures that the gene product is endogenously processed, leading to the generation of MHC class I-restricted cytotoxic T lymphocytes (CTL), the effector arm of cell-mediated immune responses. Finally, in addition to genes coding for the antigen(s), genetic modification of the DC can induce genes coding for mediators relevant to generation of the immune response to the antigen(s), further boosting host responses to the antigens presented by the modified DC. Different gene transfer approaches have been explored to genetically modify DC, including retroviral vectors (16 -18 ), recombinant vaccinia virus vectors (19 ), and recombinant adenovirus (Ad) vectors (19 -23 ). The focus of this chapter is on using recombinant Ad vectors to transfer genes to murine DC. We have used a similar strategy to transfer genes to human DC (24 ). As an example of the power of this technology, we will describe the use of Ad-vector-modified DC to suppress the growth of tumor cells modified to express a specific antigen.