Immunization with interleukin-2-secreting allogeneic mouse fibroblasts expressing melanoma-associated antigens prolongs the survival of mice with melanoma.

The survival of C57BL/6 mice (H-2b) bearing B16 melanoma (H-2b) was prolonged if the animals were treated solely by immunization with an interleukin-2 (IL-2)-secreting allogeneic cell construct that expressed melanoma-associated antigens (MAA) along with major histocompatibility complex (MHC) class-I determinants (H-2k; RLBA-IL-2 cells). This was the case if the mice were immunized simultaneously with, or 6 days following, the injection of viable B16 cells. Under similar conditions, the survival of tumor-bearing mice immunized with an allogeneic cell construct (H-2k) that expressed MAA but did not secrete IL-2 (RLBA-ZipNeo cells), or with an allogeneic construct (H-2k) that secreted IL-2 but did not form MAA (LM-IL-2 cells), was also prolonged. However, in these instances, the period of survival was significantly shorter than that of mice immunized with the cell construct that combined IL-2 secretion with the expression of MAA. Tumor-bearing mice immunized with non-transfected LM(TK-) cells (H-2k), or irradiated B16 cells (H-2b) failed to survive longer than untreated mice. Although the survival of the treated animals was prolonged, in most instances tumor growth recurred. The recurrent tumors in mice treated with the allogeneic cell constructs formed melanin and were histologically indistinguishable from tumors in untreated mice. Cells from the recurrent tumors were resistant to further immunotherapy and to cytotoxic effector cells obtained from the spleens of mice immunized with the same cellular immunogen used initially. The injection of IL-2-secreting syngeneic B16 cells into C57BL/6 mice invariably resulted in the appearance of non-IL-2-secreting melanomas. Under similar circumstances, tumors failed to develop in C57BL/6 mice injected with IL-2-secreting, or non-secreting, allogeneic cell constructs. Thus, the expression of allogeneic antigens protected the mice from growth of the cellular immunogens.