Newcastle disease virus (NDV) is a negative sense RNA paramyxovirus of birds which in human tumor cells, in contrast to human non-tumor cells, has shown replication competence leading to tumor cell death (i.e., tumor selectivity and viral oncolysis). Our study demonstrates that this virus induces high levels of pro-inflammatory cytokines in the bronchial lavage fluid of mice after nasal application and also in vitro in human dendritic cells (DCs). NDV is known as a very efficient inductor of type I interferon (IFN). The presented data show the key role played by the cell surface receptor to type I IFN (IFNAR) but not by the interferon transcription factors IRF-3 and IRF-7 in the induction of the important pro-inflammatory cytokine IL-12 upon transcription of NDV genes in DCs. We show that NDV activates in infected cells the helicase RIG-I. In Tregs, the activation of RIG-I was shown in other studies to inhibit the suppressive function of these cells. We thus conclude that NDV in tumor therapy may help to stimulate T effector cells but also to block Treg cells, thereby alleviating a brake to antitumor activity.

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