Enhanced Sensitivity to IL-2 Signaling Regulates the Clinical Responsiveness of IL-12–Primed CD8+ T Cells in a Melanoma Model

The optimal expansion, trafficking, and function of adoptively transferred CD8+ T cells are parameters that currently limit the effectiveness of antitumor immunity to established tumors. In this study, we addressed the mechanisms by which priming of self tumor-associated Ag-specific CD8+ T cells influenced antitumor functionality in the presence of the inflammatory cytokine IL-12. In vitro priming of mouse tumor-specific CD8+ T cells in the presence of IL-12 induced a diverse and rapid antitumor effector activity while still promoting the generation of memory cells. Importantly, IL-12–primed effector T cells dramatically reduced the growth of well-established s.c. tumors and significantly increased survival to highly immune resistant, established intracranial tumors. Control of tumor growth by CD8+ T cells was dependent on IL-12–mediated upregulation of the high-affinity IL-2R (CD25) and a subsequent increase in the sensitivity to IL-2 stimulation. Finally, IL-12–primed human PBMCs generated tumor-specific T cells both phenotypically and functionally similar to IL-12–primed mouse tumor-specific T cells. These results highlight the ability of IL-12 to obviate the strict requirement for administering high levels of IL-2 during adoptive cell transfer-mediated antitumor responses. Furthermore, acquisition of a potent effector phenotype independent of cytokine support suggests that IL-12 could be added to adoptive cell transfer clinical strategies in cancer patients.