Abstract
Modified vaccinia virus Ankara (MVA) is an attenuated double-stranded DNA poxvirus currently developed as a vaccine vector against HIV/AIDS. Profiling of the innate immune responses induced by MVA is essential for the design of vaccine vectors and for anticipating potential adverse interactions between naturally acquired and vaccine-induced immune responses. Here we report on innate immune sensing of MVA and cytokine responses in human THP-1 cells, primary human macrophages and mouse bone marrow-derived macrophages (BMDMs). The innate immune responses elicited by MVA in human macrophages were characterized by a robust chemokine production and a fairly weak pro-inflammatory cytokine response. Analyses of the cytokine production profile of macrophages isolated from knockout mice deficient in Toll-like receptors (TLRs) or in the adapter molecules MyD88 and TRIF revealed a critical role for TLR2, TLR6 and MyD88 in the production of IFNβ-independent chemokines. MVA induced a marked up-regulation of the expression of RIG-I like receptors (RLR) and the IPS-1 adapter (also known as Cardif, MAVS or VISA). Reduced expression of RIG-I, MDA-5 and IPS-1 by shRNAs indicated that sensing of MVA by RLR and production of IFNβ and IFNβ-dependent chemokines was controlled by the MDA-5 and IPS-1 pathway in the macrophage. Crosstalk between TLR2-MyD88 and the NALP3 inflammasome was essential for expression and processing of IL-1β. Transcription of the Il1b gene was markedly impaired in TLR2−/− and MyD88−/− BMDM, whereas mature and secreted IL-1β was massively reduced in NALP3−/− BMDMs or in human THP-1 macrophages with reduced expression of NALP3, ASC or caspase-1 by shRNAs. Innate immune sensing of MVA and production of chemokines, IFNβ and IL-1β by macrophages is mediated by the TLR2-TLR6-MyD88, MDA-5-IPS-1 and NALP3 inflammasome pathways. Delineation of the host response induced by MVA is critical for improving our understanding of poxvirus antiviral escape mechanisms and for designing new MVA vaccine vectors with improved immunogenicity.
Highlights
Attenuated poxviruses are currently being developed as vaccines vectors against various infectious diseases including HIV, malaria and tuberculosis [1]
Innate immune responses elicited by Modified vaccinia virus Ankara (MVA) The profile of innate immune responses elicited by MVA was first examined by RT-PCR and ELISA in a mouse model of poxvirus infection [23]
Having identified the pathogen recognition receptors implicated in macrophage response to MVA (TLR2-TLR6, MDA-5 and NALP3), we examined which downstream signalling pathways are activated for the expression of cytokines, chemokines and type I IFNs
Summary
Attenuated poxviruses are currently being developed as vaccines vectors against various infectious diseases including HIV, malaria and tuberculosis [1]. Modified vaccinia virus Ankara (MVA) and NYVAC are highly attenuated poxvirus strains due to multiple deletions of viral genes and are replication-deficient in human cells. MVA is a leading vaccine candidate for delivery of HIV genes with efficient induction of T-cell mediated immune responses [1–3]. Profiling of the immune responses triggered by poxvirus vaccine vectors is critical for optimal design of vaccine vectors and for anticipating potential harmful interactions between naturally acquired or vaccine-induced immune responses against the vaccine target. This is an important lesson learned from the adenovirus type 5 (Ad5) HIV vaccine (MRKAd5) STEP trial. The need for extensive assessments of vaccine-induced innate and adaptive immune responses to prevent unexpected adverse events
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