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Dendritic cell (DC)-based tumor vaccine represents a promising therapeutic approach, but has only achieved limited success in the clinic. The major obstacle is that the current DC vaccine immunization only elicits weak CTL responses against self tumor-associated antigens that are insufficient to break self-tolerance at the host level. Recent studies indicate the immunostimulatory potency of DCs is inhibited by negative regulators of proinflammatory signal transduction pathways such as the suppressor of cytokine signaling (SOCS1). SOCS1 is an inducible, negative feedback regulator of JAK/STAT signal transduction pathways and the inhibition of SOCS1 significantly enhances the sensitivity of mouse bone-marrow-derived DCs to stimulation with TLR agonists. In this study, we investigated the immunostimulatory potency of a human PBMC-derived DC vaccine that coexpresses a SOCS1-siRNA, tumor-associated antigen, and TLR agonist. We constructed and produced a recombinant adenovirus (Ad-siSSF) which co-expresses hSOCS1-siRNA, tumor-associated antigen (a transdominant negative survivin mutant), and bacterial flagellin, a ligand for TLR5. We also generated a recombinant adenovirus (Ad-S) expressing the transdominant negative survivin mutant as control. We found that human PBMC-derived DCs transfected with Ad-siSSF showed enhanced expression of co-stimulatory molecules such as CD40, CD80, CD86 and chemokine receptors such as CCR7, in comparison with human DCs transfected with Ad-S or Ad-CMV controls. Increased levels of pro-inflammatory cytokines and chemokines, including IL-6, IL-12, IFN-γ, TNF-α, and Rantes, were produced by human DCs transfected with Ad-siSSF. In vitro assays further demonstrated that the transduced human DCs had an enhanced migration function in response to chemokines. Further study is under way to investigate the immunostimulatory potency of the human DC vaccine to activate antigen-specific CTL responses in vitro and in SCID-hu mouse models.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA