Dendritic cells (DCs) are potent antigen-presenting cells responsible for the activation and functional polarization of specific T cells. In patients with renal cell carcinoma (RCC) and other cancers, coordinate DC and T cell defects have been reported. In particular, DC and T cell functional subsets that are not conducive to tumor clearance are hypothesized to predominate in patients with advanced-stage disease. Two major peripheral blood DC subsets have been identified in humans: myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) that are believed to mediate contrasting effects on cancer immunity. Given the lack of information regarding DC subsets in patients with RCC, in the present study we have investigated the comparative frequencies and activation states of mDC and pDC in peripheral blood, cancer tissues and lymph nodes of patients with RCC using flow cytometry and immunohistochemistry. Three monoclonal antibodies (mAbs) reactive against specific DC subsets (BDCA-2 or BDCA-4 for pDC and BDCA-1 and BDCA-3 which represent two distinct subsets of mDC, mDC1 and mDC2, respectively) were employed. We observed a significant reduction of both DC subsets in the peripheral blood of patients as compared to normal donors. Similarly, both mDC and pDC were recruited in large numbers into RCC tumor tissues, where they displayed an immature phenotype (DC-LAMP(-)) and appeared unable to differentiate into mature DC (CD83(+)) that were competent to migrate to draining lymph nodes. However, we were readily able to generate ex vivo mDC from RCC patients. These DC stimulated robust anti-tumor CTL in vitro and would be envisioned for use in DC-based vaccines applied in patients with RCC whose existing immune system is judged dysfunctional, anergic or prone to undergo apoptosis.