Heterogeneous Interleukin-15 Inducibilities in Murine B16 Melanoma and RM-1 Prostate Carcinoma by Interferon-α Treatment

Abstract

Long-term treatment of mouse cancer cells with interferon-α (IFN-α) converts parental B16 melanoma cells to B16α vaccine cells. Inoculation of syngeneic mice with UV-irradiated B16α vaccine cells triggers immunity to the parental B16 tumor that is mediated by host macrophages, T cells, and NK cells. Lymph node cells from mice inoculated with irradiated B16α vaccine cells, but not with irradiated parental cells, proliferate when cultured in vitro, suggesting long-term in vivo activation of lymphoid cells. Both IL-15 mRNA and IL-15 protein are highly induced in B16α vaccine cells. The bulk of the induced IL-15 is shown to be cell-associated, either cytoplasmic or membranous. The current study investigated the feasibility of applying the B16α vaccination protocol to generate a cancer vaccine against murine RM-1 prostate carcinoma. In comparison to B16α vaccine cells, long-term IFN-α–treated RM-1 cells (RM-1α vaccine cells) showed significant IL-15 mRNA induction but relatively low IL-15 protein up-regulation. When UV-irradiated, a 3-fold increase in intracellular IL-15 was observed in RM-1α vaccine cells, suggesting UV damage may have negated a possible control mechanism for IL-15 synthesis. Efficacy of in vivo vaccination of syngeneic mice with UV-irradiated RM-1α and B16α vaccine cells showed correlation between high IL-15 level and high vaccine efficacy in B16α cells compared to low IL-15 level and low vaccine efficacy in RM-1α cells. This supports the concept that the induction of IL-15 in tumor cells can be useful for creating whole-cell cancer vaccines.