Synergistic effects of IL-12 and IL-18 in skewing tumor-reactive T-cell responses towards a type 1 pattern.

We have previously described the antitumor reactivity of tumor-draining lymph node (TDLN) cells after secondary activation with antibodies. In this report, we examined the effects of interleukin (IL)-12 and IL-18 on modulating the immune function of antibody-activated murine TDLN cells. TDLN cells were activated with anti-CD3/anti-CD28 monoclonal antibody followed by stimulation with IL-12 and/or IL-18. IL-18 in combination with IL-12 showed a synergistic effect in augmenting IFNgamma and granulocyte macrophage colony-stimulating factor secretion, whereas IL-18 alone had minimal effect. Concurrently, IL-18 prevented IL-12-stimulated TDLN cells from producing IL-10. The IL-12/IL-18-cultured TDLN cells therefore manifested cytokine responses skewed towards a Th1/Tc1 pattern. IL-12 and IL-18 stimulated CD4(+) TDLN cells and enhanced IFNgamma production by CD4(+) cells to a greater extent than by CD8(+) cells. Use of NF-kappaB p50(-/-) TDLN cells suggested the involvement of NF-kappaB in the IL-12/IL-18 polarization effect. Furthermore, a specific NF-kappaB inhibitor significantly suppressed IL-12/IL-18-induced IFNgamma secretion, thus confirming the requirement for NF-kappaB activation in IL-12/IL-18 signaling. In adoptive immunotherapy, IL-12- and IL-18-cultured TDLN cells infiltrated pulmonary tumor nodules and eradicated established tumor metastases more efficiently than T cells generated with IL-12 or IL-18 alone. Antibody depletion revealed that both CD4(+) and CD8(+) cells were involved in the tumor rejection induced by IL-12/IL-18-cultured TDLN cells. These studies indicate that IL-12 and IL-18 can be used to generate potent CD4(+) and CD8(+) antitumor effector cells by synergistically polarizing antibody-activated TDLN cells towards a Th1 and Tc1 phenotype.