2563 Background: We have reported positive immunological and clinical results in patients treated with an autologous tumor cell vaccine modified with the hapten, dinitrophenyl (DNP). Now we have developed a second generation technology consisting of irradiated, autologous tumor cells, half of which are modified with DNP and half with a second hapten, sulfanilic acid (SA). Methods: Freshly-dissociated, cryopreserved tumor cells (TC) are irradiated (2500 cGy); then half of the cells are modified with DNP and half with SA. After combining them, the “mixed haptenized” cells are fixed in a low concentration of ethanol, aliquotted, and frozen. Each vaccine batch is tested for sterility, endotoxin, and flow cytometric expression of melanoma-associated antigens. In an ongoing phase I–II trial, patients with stage IV melanoma are administered the vaccine at one of three dosage levels (0.05x106, 0.50 x106, or 5.0 x106 cells/dose) using a previously determined optimal schedule of administration. Before and after a 1...