The dendritic cell (DC) is a newly discovered member of the immune system specialized in presenting antigen to naive T cells, and consequently playing a central role in the induction of T cell, as well as B-cell, immunity. Immunization with DC loaded with tumor antigens could, therefore, represent a powerful method of inducing antitumor immunity. Studies in our laboratory have shown that DC transfected with mRNA encoding tumor antigens are effective inducers of cytotoxic T cells (CTL) and tumor immunity. Tumor RNA can be amplified from microscopic amounts of tumor tissue obtained by microdissection from needle biopsies or fixed tissue sections providing virtually inexhaustible amounts of tumor antigens without the need to identify the relevant antigens in each patient. Phase I/II clinical studies in patients with prostate and renal cancer have established the safety, and feasibility of this approach and despite the advanced nature of the disease, the majority of the patients exhibited specific immunological responses. To enhance the therapeutic impact of this vaccination strategy antisense and siRNA technology are used to induce CD4+ T cell immunity by inhibiting Invariant chain expression in the (mRNA transfected) DC, and CTLA-4 binding RNA aptamers are used to enhance the persistence of vaccine-induced antitumor immunity.