Generation of potent anti-tumor immunity in mice by interleukin-12-secreting dendritic cells
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To induce cytolytic immunity, dendritic cells (DCs) need to release bioactive interleukin-12 (IL-12) p70 heterodimeric molecules. To study the role of IL-12 for the generation of an anti-tumor immune response, we generated two classes of DCs. (1) DCs were initiated to secrete IL-12 by exposure to LPS/IFN-γ for 2 h resulting, as demonstrated in vitro, in continued IL-12 release for another 24 h (termed active DCs). (2) DCs were exposed to LPS/IFN-γ for 24 h and injected into mice at a time point when IL-12 production had ceased (termed exhausted DCs). These two classes of DCs were probed for their capacity to induce a cytolytic anti-tumor immune response in vivo in a syngeneic mouse tumor model. The mouse tumor cell line K-Balb was engineered to express neomycin phosphotransferase (NPT) as a model tumor antigen. DCs were charged with various NPT-derived antigens, including recombinant NPT protein, whole tumor cell lysate and NPT-derived synthetic peptides, and the induction of in vivo anti-tumor immunity was determined by measuring tumor growth. Only the injection of active DCs, i.e., cells that maintained the capacity to secrete IL-12, but not exhausted DCs that had lost the ability to produce IL-12, resulted in a measurable deceleration of growth of K-Balb-NPT tumors. This anti-tumor immune response was most pronounced when using recombinant protein as an antigen source, which was evident in a prophylactic as well as in a therapeutic setting. The absence of a response to parental K-Balb tumors confirmed the antigen specificity of the anti-tumor immune response. Together these data provide evidence for the unique capacity of actively IL-12 secreting DCs to trigger effective anti-tumor immunity using exogenous tumor antigens.
KeywordsAntigen presenting cell (APC) Dendritic cell (DC) Interleukin-12 (IL-12) Cytotoxic T lymphocyte (CTL) Cytolytic anti-tumor immune response
The work of the authors is supported by numerous private donations to the Children’s Cancer Research Institute that partly funded this study and by grants from the Austrian Industrial Research Promotion Fund (Forschungsförderungsfond der Gewerblichen Wirtschaft, Projektnummer 804445), the Vienna Business Agency (Wiener Wirtschaftsförderungsfond) and the Austrian National Bank (Jubiläumsfond der Österreichischen Nationalbank, Projektnummer 7774). We thank Eva Schmitt for excellent technical assistance and Peter Kinross for carefully reading the manuscript.
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