619. Augmentation of Anti-Tumor Activity of a Recombinant Adeno-Associated Virus 2 Carcinoembryonic Antigen Vaccine with Plasmid Adjuvants

Abstract

RECOMBINANT adeno-associated virus (rAAV) vectors have been successfully used for sustained expression of therapeutic genes. We investigated the potential of using rAAV-2 as a cancer vaccine vector and the impact of plasmid adjuvants on this activity. C57BL/6 mice received a single intramuscular injection of rAAV expressing the human tumor-associated antigen, carcinoembryonic antigen (CEA). Three weeks later, when CEA expression was optimal, plasmids encoding either mouse granulocyte macrophage-colony stimulating factor (pGM-CSF) or stromal-derived factor (pSDF) 1a or an empty plasmid vector was injected into the same muscle. Mice were challenged one week after the plasmid delivery with syngeneic MC38 tumor cells stably expressing CEA. Immunization with rAAV-CEA alone resulted in sustained transgene expression and the elicitation of a humoral immune response to CEA. Cellular immune response, however, was weak, and tumor protection was not observed. In contrast, immunization with rAAV-CEA and any of the plasmid adjuvants resulted in stronger cellular immune responses to CEA and tumor protection. The addition of plasmid adjuvants increased dendritic cell recruitment in situ. Infiltration of myeloid dendritic cells was observed when either pGM-CSF or the empty vector was applied as adjuvant. Infiltration of plasmacytoid dendritic cells was observed in rAAV-CEA and pSDF-1a immunized mice. The addition of the plasmid adjuvants also increased the production of interferon-gamma in cytokine release assay. These data indicate that robust rAAV transgene expression of a tumor antigen followed by transient plasmid delivery to recruit and activate dendritic cells is an effective method of eliciting anti-tumor cellular immune responses.