Soluble murine melanoma-associated antigens (MAA), partially purified from the media of B16 melanoma cells in culture by ammonium sulfate precipitation and Sephadex G-200 chromatography, were tested for their effect on tumor growth. MAA were immunogenic in syngeneic mice as evidenced by their ability to induce anti-melanoma antibodies and partial protective tumor immunity. The level of immunity was variable. It ranged from retardation of tumor development to almost complete suppression of tumor growth. The results were influenced by the nature of the control group, since immunization to either normal tissue antigens or complete Freund's adjuvant enhanced tumor growth. Overall, 46 of 91 MAA immunized mice, but none of 114 control mice, survived over 6 weeks (p < 0.001). The protective immunity was specific since MAA immunized mice were not resistant to challenge with an unrelated syngeneic tumor (BW 10232 adenocarcinoma). Partially purified normal tissue antigens were also immunogenic in syngeneic mice. They induced low levels of antibodies to, and enhanced the growth of, melanoma.
These findings indicate that the culture media of melanoma cells contains tumor antigens that retain their biologic activity after partial purification, and that can induce specific, although only partial, protective immunity to melanoma.