Newcastle disease virus induces pro-inflammatory conditions and type I interferon for counter-acting Treg activity

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.

Importance of retinoic acid-inducible gene I and of receptor for type I interferon for cellular resistance to infection by Newcastle disease virus

Newcastle disease virus (NDV) is an avian paramyxovirus with oncolytic properties which shows promising effects in the treatment of cancer. Anti-cancer effects are due to the virus ability: i) to replicate in and kill tumor cells, leading finally to their selective elimination; and ii) to induce the stimulation of antitumor activities in immune cells. NDV does not harm normal cells and has a high safety profile. In this study, we first report a direct correlation between the degree of cell resistance to NDV infection and the cellular expression of the retinoic acid-inducible gene I (RIG-I) which is a cytosolic viral RNA receptor. RIG-I plays an important role in the recognition of and response to infection by RNA viruses. We also demonstrate that impairment of the interferon (IFN) pathway through deletion of the receptor for type I IFN (IFNR1) in primary macrophages leads to NDV replication. In tumor cells, addition of exogenous IFN-α4 is shown to lead to tumor growth reduction and inhibition of viral replication. Finally, increase of the RIG-I concentration of tumor cells via plasmid transfection is shown to be associated with a stronger resistance to NDV infection. These findings shed new light on the crucial role played by the cytosolic receptor RIG-I and the plasma membrane receptor IFNR1 as key molecules to protect cells against infection by NDV.

Important role of interferon regulatory factor (IRF)-3 in the interferon response of mouse macrophages upon infection by Newcastle disease virus

Newcastle disease virus (NDV) is an interesting agent for activating innate immune activity in macrophages including secretion of TNF-α and IFN-α, upregulation of TRAIL and activation of NF-κB and iNOS. However, the molecular mechanism of such cellular activities remains largely unknown. Tumor selectivity of replication of NDV has been described to be linked to deviations in tumor cells of the type I interferon response. We therefore focused on the interferon response to NDV of macrophages as part of innate anti-viral and anti-tumor activity. In particular, we investigated the functional significance of the interferon regulatory factor genes (IRF)-3 and IRF-7. Deletion of the IRF-3 or IRF-7 gene was found to increase susceptibility of mouse macrophages to virus infection. Surprisingly, NDV replicated better in IRF-3 KO than in IRF-7 KO macrophages. Further analysis showed that IRF-3 KO macrophages have a lower basal and NDV-induced RIG-I expression in comparison to IRF-7 KO macrophages. This might explain why, in IRF-3 KO macrophages, the secretion of type I interferons after NDV infection is delayed, when compared to IRF-7 KO and wild-type macrophages. In addition, IRF-3 KO cells showed reduced NDV-induced levels of IRF-7. This effect could be prevented by priming the cells first by interferon-α. Further results indicated that an early production of type I interferon rather than high maximal levels at later time points are important for resistance to infection by NDV. In conclusion, these results demonstrate an important role of IRF-3 for the innate anti-viral response to NDV of mouse macrophages.

Expression of RIG-I, IRF3, IFN-beta and IRF7 determines resistance or susceptibility of cells to infection by Newcastle Disease Virus

Newcastle Disease Virus (NDV) is an avian paramyxovirus with anti-neoplastic and immune-stimulatory properties which has raised considerable interest for cancer therapy. To better understand the molecular nature of the tumor selective replication of NDV, we investigated the cellular responses of murine normal and tumor cells after infection by NDV. To this end, we compared the basal expression of different antiviral proteins as well as the expression induced by the addition of NDV to the cells in vitro and in vivo. Primary macrophages were found to be resistant to NDV infection and exhibited a high basal and induced expression of various antiviral genes. In contrast, macrophage-derived RAW tumor cells were highly susceptible to NDV infection and displayed a low expression of several antiviral genes. Macrophage-derived J774 tumor cells were intermediate with regard to NDV replication and antiviral gene expression. The responsiveness to exogenously added IFN-alpha was found highest in normal macrophages, lowest in the RAW cells, and intermediate in the J774 cells. We also analysed dendritic cells as well as additional normal and tumor cell types. A strong inverse correlation was obeserved between the susceptibility to infection and the basal expression of the antiviral genes RIG-I, IRF3, IRF7 and IFN-beta. A strong expression of these genes can explain the resistance of normal cells to NDV infection and a weak antiviral gene expression the broad susceptibility of tumor cells.

In vivo efficacy of systemic tumor targeting of a viral RNA vector with oncolytic properties using a bispecific adapter protein

The aim of the study was: i) to specifically target tumor tissue by Newcastle disease virus (NDV) with oncolytic properties, ii) to improve the delivery system for systemic application of NDV via a bispecific adapter protein and iii) to investigate anti-tumor activity and side-effects. We selected two oncolytic virus strains, one native and the other recombinant, which showed multicyclic replication patterns in tumor cells. In order to reduce normal cell binding, they were modified by preincubation with a recombinant bispecific protein which blocks the viral native cell binding site and introduces a new binding site for a tumor-associated target (in this study, the interleukin-2-receptor, IL-2R). After intravenous transfer to mice, uptake of modified NDV in liver, spleen, kidney and lung was greatly reduced in comparison to unmodified NDV as determined by RRT-PCR of viral M gene copies. In IL-2R+ tumor bearing mice, the same assay revealed a high replication efficiency of the modified virus in the tumor tissue. Tumor therapy experiments showed that the side-effects induced by systemic application were greatly reduced by the adapter protein and that the anti-tumor effects were mostly undiminished. The demonstration of significant systemic anti-tumor activity of this viral vector suggests potential for augmentation by inclusion of one or more therapeutic genes.