In Vivo Visualizing the IFN-ß Response Required for Tumor Growth Control in a Therapeutic Model of Polyadenylic-Polyuridylic Acid Administration.

The crucial role that endogenously produced IFN-ß plays in eliciting an immune response against cancer has recently started to be elucidated. Endogenous IFN-ß has an important role in immune surveillance and control of tumor development. Accordingly, the role of TLR agonists as cancer therapeutic agents is being revisited via the strategy of intra/peritumoral injection with the idea of stimulating the production of endogenous type I IFN inside the tumor. Polyadenylic-polyuridylic acid (poly A:U) is a dsRNA mimetic explored empirically in cancer immunotherapy a long time ago with little knowledge regarding its mechanisms of action. In this work, we have in vivo visualized the IFN-ß required for the antitumor immune response elicited in a therapeutic model of poly A:U administration. In this study, we have identified the role of host type I IFNs, cell populations that are sources of IFN-ß in the tumor microenvironment, and other host requirements for tumor control in this model. One single peritumoral dose of poly A:U was sufficient to induce IFN-ß, readily visualized in vivo. IFN-ß production relied mainly on the activation of the transcription factor IFN regulatory factor 3 and the molecule UNC93B1, indicating that TLR3 is required for recognizing poly A:U. CD11c(+) cells were an important, but not the only source of IFN-ß. Host type I IFN signaling was absolutely required for the reduced tumor growth, prolonged mice survival, and the strong antitumor-specific immune response elicited upon poly A:U administration. These findings add new perspectives to the use of IFN-ß-inducing compounds in tumor therapy.

Direct effect of dsRNA mimetics on cancer cells induces endogenous IFN-ß production capable of improving dendritic cell function.

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-ß autocrine loop, dsRNA-elicited IFN-ß production improves dendritic cell (DC) functionality. Human A549 lung and DU145 prostate carcinoma cells significantly responded to poly I:C stimulation, producing IFN-ß at levels that were capable of activating STAT1 and enhancing CXCL10, CD40, and CD86 expression on human monocyte-derived DCs. IFN-ß produced by poly I:C-activated human cancer cells increased the capacity of monocyte-derived 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-ß production and contribute to the antitumoral response.

IFNß produced by TLR4-activated tumor cells is involved in improving the antitumoral immune response.

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 (lps-del)). Under such conditions, B16 cells yielded smaller tumors than nonstimulated B16 cells. The apoptosis/proliferation balance of the cells was not modified by TLR ligand treatment, nor was this effect compromised in immunocompromised nude mice. Mechanistic investigations revealed that IFNß was the critical factor produced by TLR4-activated tumor cells in mediating their in vivo outgrowth. Transcriptional analysis showed that TLR4 activation on B16 cells induced changes in the expression of type I IFN and type I IFN-related genes. Most importantly, culture supernatants from LPS-B16 cells improved the maturation of bone marrow-derived dendritic cells (BMDC) from TLR4-deficient mice, upregulating the expression of interleukin-12 and costimulatory molecules on those cells. BMDC maturation was blunted by addition of an IFNß-neutralizing antibody. Moreover, tumor growth inhibition observed in LPS-B16 tumors was abrogated in IFNAR1-deficient mice lacking a functional type I IFN receptor for binding IFN. Together, our findings show that tumor cells can be induced through the TLR4 pathway to produce IFN and positively contribute to the antitumoral immune response.