Cross-presentation of a human tumor antigen delivered to dendritic cells by HSV VP22-mediated protein translocation.

Dendritic cells (DC) capture antigens from apoptotic and/or necrotic tumor cells and cross-present them to T cells, and various ways of delivering tumor antigens to DC in vitro and in vivo are being pursued. Since fusions of antigenic proteins with the HSV integument protein VP22 are capable of intercellular trafficking, this approach has been exploited for delivery of antigens to antigen-presenting cells. Adenoviral vectors were used to express the tumor-associated-but-self-antigen MART-1 fused to HSV VP22 in MART-1-negative A375 melanoma cells and in DC. When expressed in A375 cells and allowed to spread to DC across a transwell barrier, the VP22-MART-1 fusion protein localized to both early and late endosomal structures of the DC. The DC loaded with the VP22-MART-1 fusion by intercellular trafficking efficiently presented the MART-1(27-35) epitope to MART-1(27-35)-specific CTL. Furthermore, transloaded DC were capable of expanding the population of MART-1(27-35)-specific CTL. Thus, a tumor antigen acquired by intercellular trafficking can be cross-presented by DC. This experimental approach should therefore be useful not only for studying the mechanism of cross-presentation but also for vaccine development.