Enhancing dendritic cell vaccine potency by combining a BAK/BAX siRNA‐mediated antiapoptotic strategy to prolong dendritic cell life with an intracellular strategy to target antigen to lysosomal compartments

Dendritic cell (DC)‐based vaccines have become important in immunotherapeutics as a measure for generating antitumor immune responses. We have previously demonstrated that linkage of the antigen gene to a lysosomal targeting signal, a sorting signal of the lysosome‐associated membrane protein type 1 (LAMP‐1), enhances the potency of DC‐based vaccines. DCs have a limited life span, hindering their long‐term ability to prime antigen‐specific T cells. In this study, we attempted to further improve the potency of a DC vaccine that targets human papilloma virus 16 (HPV16) E7 to a lysosomal compartment (DC‐Sig/E7/LAMP‐1) by combining a strategy to prolong DC life. We show that small interfering RNA‐targeting Bak and Bax proteins can be used to allow transfected DCs to resist being killed by T cells. This is done by downregulating these proapoptotic proteins, which have been known as so‐called gate keepers in mitochondria‐mediated apoptosis. DCs expressing intact E7 or Sig/E7/LAMP‐1 became resistant to attack by CD8 + T cells after transfection with BAK/BAX siRNA, leading to enhanced E7‐specific T cell activation in vitro and in vivo . More importantly, vaccination with E7‐presenting DCs transfected with BAK/BAX siRNA generated a strong therapeutic effect against an E7‐expressing tumor in vaccinated mice, compared with DCs transfected with control siRNA. Our data indicate that a combination of strategies to enhance intracellular Ag processing and to prolong DC life may offer a promising strategy for improving DC vaccine potency. © 2007 Wiley‐Liss, Inc.