IFN{gamma} markedly cooperates with intratumoral dendritic cell vaccine in dog tumor models.

Dendritic cell (DC)-based immunotherapy can trigger effective immune responses against cancer in human patients. Although accompanied by little toxicity, further improvements are needed to optimize immune responses for fully satisfactory clinical outcomes. IFNγ, a potent inducer of T helper type 1 immune responses, is considered an important tool to realize improvements. In this study, we sought to clarify the effect of IFNγ on the maturation and activation of DCs and the clinical outcome of DC-based cancer therapy in dogs. In vitro experiments indicated that IFNγ significantly enhanced the expression of immune stimulatory molecules and interleukin-12 by DCs derived from canine monocytes. IFNγ also significantly strengthened DC-mediated growth suppression against tumor cell lines. DC inoculation with concomitant delivery of IFNγ into primary or recurrent tumors elicited significant clinical responses, including four complete responses and two partial responses against malignant tumors, also eliciting partial responses against benign but actively growing tumors. Together, our results indicate that combining IFNγ and DCs could induce strong immune responses against tumors, significantly improving clinical outcomes. The present study of dogs bearing common types of cancer in humans offers a unique line of support for the development of human cancer therapies.

Effect of IL-12 on canine dendritic cell maturation following differentiation induced by granulocyte-macrophage CSF and IL-4.

IL-12 is a cytokine produced by dendritic cells (DC) and activates cytotoxic T cells and NK cells against tumors. We investigated the effect of IL-12 on DC. When peripheral blood monocytes were incubated with canine granulocyte-macrophage (GM)-CSF and IL-4, expression of MHC class II, CD1a, CD80 and CD86 was significantly elevated, but the cell morphology was that of immature DC. By adding canine IL-12 to the DC-inducing culture, expression of CD80 and CD1a was significantly enhanced, and the cell morphology shifted to that of mature DC. T cell stimulation by cultured cells was also significantly enhanced by the presence of IL-12. These results show that IL-12 significantly promotes the maturation and activation of canine DC following the induction of differentiation by GM-CSF and IL-4.

Construction of an expression vector for improved secretion of canine IL-18.

To construct a vector for caspase-1 independent expression of canine IL-18, the signal sequence of canine IL-12p40 was fused to the sequence of mature IL-18 on the NdeI restriction site which is located at the 3' end of the signal sequence. The resulting vector expressed coding protein from transfected mammalian cells. The expressed protein was shown to have IL-18 bioactivity in a INF-gamma-inducing assay. These results suggest that the expression vector is the desired tool for advancement of dendritic cell (DC)-based cancer therapy, provided that the vector can successfully be transfected into dendritic cells. We propose a simple and widely applicable method for providing the signal sequence.