CD40 and renal cell carcinoma: The extracellular CD40L domain of the CSP is key to this double action approach since its receptor, CD40, is aberrantly expressed by many tumor cells, including RCC and melanoma, and is also expressed on tumor stroma, including antigen presenting cells, tumor-associated macrophages (45–48, 52) and tumor endothelial cells (40–42) (see Figure 1).