Immunization of Mice with Allogeneic Fibroblasts Genetically Modified for Interleukin-2-Secretion and Expression of Melanoma-Associated Antigens Stimulate Predetermined Classes of Anti-Melanoma Effector Cells

Immunization of C57BL/6 mice (H-2^b) with a mouse fibroblast cell-line of C3H origin (H-2^k) genetically modified for interleukin-2 (IL-2)-secretion and the expression of melanoma-associated antigens (MAAs) (RLBA-IL-2 cells) resulted in a systemic anti-melanoma cellular immune response that led to a prolongation of survival of mice with established melanoma. Here we report certain of the effector cell-types activated for anti-melanoma immunity in mice immunized with the modified cells and, for comparison, the anti-melanoma cell-types activated following immunization with IL-2-secreting, MAA-negative fibroblasts (LM-IL-2 cells) or with non-IL-2-secreting, MAA-positive fibroblasts (RLBA-ZipNeo cells). The data indicate that both Lyt-2.2⁺(CD8⁺) and natural killer/lymphokine-activated killer (NK/LAK) cells with anti-melanoma cytotoxicity were predominant in mice immunized with RLBA-IL-2 cells. NK/LAK cells alone were predominant in mice immunized with LM-IL-2 cells, and Lyt-2.2⁺cells were predominant in mice immunized with RLBA-ZipNeo cells. The involvement of L3T4⁺(CD4⁺) cells in the effector phase of the response was not detected in mice immunized with the genetically modified cells. Immunization of mice with both LM-IL-2 cells and RLBA-ZipNeo cells resulted in an anti-melanoma response of greater magnitude than was present in mice immunized with either cell-construct alone. It was equivalent to the melanoma immunity in mice immunized with RLBA-IL-2 cells. These data indicate that the immunogenic properties of the modified cells determined the anti-melanoma effector cell-types and suggest that combination immunotherapy with cell-constructs that stimulate different classes of effector cells may be more effective in immune-mediated tumor regression than immunization with a construct that activates a single effector cell-type alone.