Toll-like receptor (TLR) ligands may be a valuable tool to promote antitumor responses by reinforcing antitumor immunity. In addition to their expression in immune cells, functional TLRs are also expressed by many cancer cells, but their significance has been controversial. In this study, we examined the action of TLR ligands on tumor pathophysiology as a result of direct tumor cell effects. B16 murine melanoma cells were stimulated in vitro with a TLR4 ligand (LPS-B16) prior to inoculation into TLR4-deficient mice (Tlr4

Viral double-stranded RNA (dsRNA) mimetics have been explored in cancer immunotherapy to promote antitumoral immune response. Polyinosine-polycytidylic acid (poly I:C) and polyadenylic-polyuridylic acid (poly A:U) are synthetic analogs of viral dsRNA and strong inducers of type I interferon (IFN). We describe here a novel effect of dsRNA analogs on cancer cells: besides their potential to induce cancer cell apoptosis through an IFN-β autocrine loop, dsRNA-elicited IFN-β production improves dendritic cell (DC) functionality. Human A549 lung and DU145 prostate carcinoma cells significantly responded to poly I:C stimulation, producing IFN-β at levels that were capable of activating STAT1 and enhancing CXCL10, CD40, and CD86 expression on human monocyte-derived DCs. IFN-β produced by poly I:C-activated human cancer cells increased the capacity of monocytederived DCs to stimulate IFN-γ production in an allogeneic stimulatory culture in vitro. When melanoma murine B16 cells were stimulated in vitro with poly A:U and then inoculated into TLR3 −/− mice, smaller tumors were elicited. This tumor growth inhibition was abrogated in IFNAR1 −/− mice. Thus, dsRNA compounds are effective adjuvants not only because they activate DCs and promote strong adaptive immunity, but also because they can directly act on cancer cells to induce endogenous IFN-β production and contribute to the antitumoral response. Keywords: Dendritic cells · dsRNA · IFN-β · TLR3 · Tumor immunityAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionPolyinosine-polycytidylic acid (poly I:C) and polyadenylicpolyuridylic acid (poly A:U) are synthetic analogs of viral doublestranded RNA (dsRNA), recognized by both Toll-like receptor 3Correspondence: Dr. Mariana Maccioni e-mail: mmaccioni@fcq.unc.edu.ar (TLR3) and RIG (retinoic acid-inducible gene)-I-like receptors (RLRs) or only TLR3, respectively [1][2][3]. These receptors are expressed mainly on APCs. Both compounds strongly enhance antigen-specific CD8 + T-cell responses, promoting antigen crosspresentation by dendritic cells (DCs), and directly acting on * These authors contributed equally to this work.C 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 1850 Gerardo Gatti et al. Eur. J. Immunol. 2013. 43: 1849-1861 effector CD8 + T cells and natural killer cells to augment IFN-γ release [4][5][6][7]. A direct effect of synthetic dsRNA on cancer cells has also been demonstrated, since they are capable of inducing the production of type I IFNs, which in turn promotes the apoptosis of cancer cells through an autocrine signaling loop [8][9][10][11]. Both poly I:C and poly A:U are strong inducers of type I IFNs. Type I IFNs can be produced by almost any cell type in the body in response to stimulation of TLR3, RLRs, and many other receptors [12]. Exogenously administered type I IFNs were used with some success (and a substantial number of toxic side effects) in anticancer therapy [13]. In contrast, the role of endogenous t...