To develop a novel dendritic cell (DC)-based vaccine for inducing antigen-specific CD8(+) T cell responses by cross-presentation, we tested a novel antigen delivery system that introduces Soluble antigens into the cytosol of cells by an endocytosis-mediated mechanism which avoids damaging the plasma membrane ("Endo-Porter"(TM)). Proteins released from endosomes into the cytoplasm are degraded by the proteasome, and fragmented antigenic peptides are presented to the classical cytosolic MHC class I pathway. DCs pulsed with OVA protein in the presence of Endo-Porter efficiently stimulate OVA peptide-specific CD8(+) T (OT-I) cells. Although this agent diverts some of the endocytosed antigens away from the classical MHC class II-restricted presentation pathway to the class I pathway, the activation of CD4(+) T cells was found not to be hampered by Endo-Porter-mediated antigen delivery. On the contrary, it was rather augmented, probably due to the increased uptake of antigen. Because specific CD4(+) T cell help is required to license DCs for cross-priming, Endo-Porter-mediated antigen delivery is a promising approach for developing more efficient cancer vaccines targeting both CD4(+) and CD8(+) T cells. (C) 2010 Elsevier Inc. All rights reserved.