Gene silencing with RNAi is an invaluable technique in cell biology to knock down the target gene expression. Dendritic cells (DC) are the most effective antigen-presenting cells (APC), and the efficacy of antigen presentation is tightly controlled by the stimulatory as well as inhibitory mechanisms. In recent studies, RNAi technology has been employed to silence the expression of the intrinsic inhibitors of antigen presentation in DC, improving the efficacy of DC vaccines against tumor antigens in pre-clinical studies. Here, we describe the technique of using siRNA oligonucleotides, adenovirus expressing shRNA (Ad-shRNA), or lentivirus expressing shRNA (Lv-shRNA) to knock down inhibitors of antigen presentation in both mouse and human DC.