GPT and melanoma: It has been also shown that a single intravenous dose of ALT-803, but not IL-15, eliminated well-established tumors and prolonged survival of mice bearing multiple myeloma,22 and that ALT-803 has superior antitumor activity over IL-15 in mice bearing subcutaneous B16F10 melanoma and CT26 colon carcinoma metastases.26 Tissue biodistribution studies in mice also revealed a much greater retention of ALT-803 in the lymphoid organs compared to IL-15, consistent with its highly potent immunostimulatory and antitumor activities in vivo.