Enhanced transduction of mouse bone marrow-derived dendritic cells by repetitive infection with self-complementary adeno-associated virus 6 combined with immunostimulatory ligands

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Abstract
The potential of adeno-associated virus (AAV)-based vectors in human gene therapy is being explored for several diseases. Although sustained transgene expression and low vector-associated cellular immunity are attractive features of recombinant (r) AAV, the wider application of rAAV vectors encapsidated in serotype 2 capsid is hampered by poor transduction efficiency in many target tissues. These include ex vivo-generated dendritic cells (DC), which have demonstrated promising immunotherapeutic activity. We report here that efficient transduction of mouse bone marrow-derived DC can be achieved with self-complementary (sc) rAAV encapsidated in serotype 6 capsid. Sequential exposure of DC precursor cultures to IL-4 and GM-CSF with sc rAAV6 encoding the human tumor antigen, carcinoembryonic antigen (CEA), for 7 days followed by activation with CpG oligodeoxynucleotides (ODN) and anti-mouse CD40 antibody resulted in highly efficient transduction of DC. DC surface markers as determined by flow cytometry analysis of sc rAAV6-transduced DC were comparable to nontransduced DC. Efficiency of vector transduction and transgene expression were confirmed by immunostaining and real-time PCR. Microarray analysis of RNA from CpG ODN and CD40 antibody stimulated sc AAV6-transduced DC revealed upregulation of transcription factors and cytokines involved in immune activation and downregulation of inhibitory factors, suggesting a possible role of transcriptional activation in the observed effect. The adoptive transfer into syngeneic mice of the ex vivo-transduced and activated DC resulted in the development of CEA-specific antibody and T-helper 1-associated immune responses. Immunized mice also developed antibody to AAV6 capsid protein, which did not crossreact with AAV2 capsid protein. These studies demonstrate the potential utility of sc rAAV serotype 6-based vectors in transduction of DC for genetic vaccination approaches.