BACKGROUNDGenetic modification of dendritic cells (DCs) has been used as an effective approach to enhance anti-tumor immunity. RNA interference (RNAi), which can cause the degradation of any RNA in a sequence-specific manner, is a post-transcriptional gene silencing mechanism. In this study, small-interfering RNA (siRNA) specific for the Ii gene was transfected into DCs, and the anti-tumor immunity of Ii-silenced DCs was assessed.

METHODSThe silencing effect of siRNA was evaluated by Western blotting and real-time PCR analyses. In vitro cytotoxic activity of T cells was evaluated using a Cytotox 96(®) non-radioactive cytotoxicity assay kit. The time to tumor onset and the tumor volumes were used as reliable indices to assess the anti-tumor immunity in vivo. To further examine the mechanisms underlying the anti-tumor immunity, flow cytometry analysis was used.

RESULTSThe Ii expression of DCs was significantly reduced after Ii siRNA transfection. Significant in vitro anti-tumor ability was exhibited when DCs were co-transfected with Ii siRNA plus endogenous tumor antigen (P < 0.05). Furthermore, tumor growth was greatly inhibited when mice were immunized with DCs transfected with Ii siRNA plus tumor antigen prior to or subsequent to tumor implantation. Flow cytometry analysis in vitro and in vivo indicated that both CD4(+) and CD8(+) T cells were significantly activated in the Ii siRNA group (P < 0.05).

CONCLUSIONSilencing of the Ii gene of DCs may offer a potential approach to enhance DC-based anti-tumor immunity.