Experiments were designed to investigate immunogenicity and therapeutic efficacy of tumour vaccines constructed by transfection of poorly immunogenic murine sarcoma Mc12 with synergistic CD80 and IL-2 genes. Immunization/challenge experiments demonstrated that both, IL-2(+) and IL-2(+) plus CD80(+) live cell vaccines can exert an immunizing stimulus, the IL-2(+) plus CD80(+) vaccine being superior to the IL-2(+) vaccine. Live CD80(+) Mc12 cell vaccine could not be tested, since the vaccine was highly tumorigenic in the doses required for immunization. Preimmunization with IL-2(+) and IL-2(+) plus CD80(+) vaccines induced regressions of a proportion of the parental Mc12 challenge inocula after their temporary growth. Areas of necrosis and extensive infiltration with Mac1(+) and CD4(+) leukocytes have been observed in the regressing sarcomas. When the therapeutic efficacy of the irradiated CD80(+), IL-2(+), and mixed CD80(+) plus IL-2(+) vaccines was compared, it was found that the insertion of the IL-2, but not CD80 gene alone was efficient. The mixed IL-2(+) plus CD80(+) tumour vaccine was able to protect and prolong survival of a higher proportion of mice than the IL-2(+) tumour vaccine.

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