Immunization with interleukin-2/interferon-γ double cytokine-secreting allogeneic fibroblasts prolongs the survival of mice with melanoma

LM mouse fibroblasts (H-2^k) were modified for the expression of (antibody-defined) melanoma-associated antigens (MAA) and the secretion of interleukin-2 (IL-2) and interferon-gamma (IFN-γ) (RLBA-IL-2/IFN-γ cells). The cell construct was tested for its immunogenic properties in C57BL/6 mice (H-2^b) with B16 melanoma. The results indicated that the survival of mice injected with a mixture of B16 cells and the modified, double cytokine-secreting fibroblasts was significantly longer than that of mice injected with B16 cells and LM cells modified for the expression of MAA and the secretion of IL-2 or IFN-γ alone (RLBA-IL-2 or RLBA-IFN-γ cells). Both natural killer/ lymphokine-activated killer (NK/LAK) cells and Lyt-2.2+CTLs with anti-melanoma cytotoxic activities were predominant in mice immunized with the double cytokine-secreting cells. B16 melanoma cells persisted in mice treated with RLBA-IL-2 cells (B16-R3). The B16-R3 cells were resistant to anti-melanoma effector cells from mice immunized with RLBA-IL-2 cells. The recurrent melanoma cells were deficient in the expression of MHC class I determinants. Class I expression by B16-R3 cells was increased if they were incubated in medium conditioned by the growth of IFN-γ-secreting RLBA-IL-2/IFN-γ or RLBA-IFN-Y cells. After incubation, the sensitivity of B16-R3 melanoma cells to immune-effector cells from mice immunized with RLBA-IL-2 cells was restored. The survival of mice bearing low MHC class l-expressing B16-R3 cells, treated RLBA-IL-2/IFN-γ cells, was determined. The treated animals survived significantly longer than mice with B16-R3 melanoma treated with RLBA-IL-2 cells. Similar results were obtained for mice with B16-R3 melanoma treated with RLBA-IFN-γ cells. We postulate that immunization of mice with IL-2/IFN-γ double cytokine-secreting cells stimulated multiple anti-melanoma effector mechanisms. Analogous to the enhanced therapeutic antitumour effects of combination chemotherapy, it was likely that treatment with a cellular immunogen engineered to stimulate more than one effector mechanism resulted in the elimination of larger numbers of tumour cells than treatment with an immunogen that stimulated a single effector mechanism alone.