Role of innate signalling pathways in the immunogenicity of alphaviral replicon-based vaccines

Abstract

BackgroundAlphaviral replicon-based vectors induce potent immune responses both when given as viral particles (VREP) or as DNA (DREP). It has been suggested that the strong immune stimulatory effect induced by these types of vectors is mediated by induction of danger signals and activation of innate signalling pathways due to the replicase activity. To investigate the innate signalling pathways involved, mice deficient in either toll-like receptors or downstream innate signalling molecules were immunized with DREP or VREP.ResultsWe show that the induction of a CD8+ T cell response did not require functional TLR3 or MyD88 signalling. However, IRF3, converging several innate signalling pathways and important for generation of pro-inflammatory cytokines and type I IFNs, was needed for obtaining a robust primary immune response. Interestingly, type I interferon (IFN), induced by most innate signalling pathways, had a suppressing effect on both the primary and memory T cell responses after DREP and VREP immunization.ConclusionsWe show that alphaviral replicon-based vectors activate multiple innate signalling pathways, which both activate and restrict the induced immune response. These results further show that there is a delicate balance in the strength of innate signalling and induction of adaptive immune responses that should be taken into consideration when innate signalling molecules, such as type I IFNs, are used as vaccine adjuvant.

NF-κB activation during intradermal DNA vaccination is essential for eliciting tumor protective antigen-specific CTL responses

“…28,29 Induction of antigen-specific T cell responses elicited by vaccination with replicon-based DNA vectors delivered intramuscularly has shown to be dependent on type I IFNs 27 while in a different study immunizing with the same kind of vector but delivered intradermally, type I IFN signaling was absolutely dispensable, and rather had a suppressive effect. 30 The contrasting results obtained by different groups seem to be related to the vaccination route, further encouraging the need of more comprehensive studies dissecting the signaling pathways activated in each particular tissue. 30 Indeed, a different situation can be observed within the tumor microenvironment, where activation of type I IFN-producing PRRs has been shown to promote potent anti-tumor effects by acting on antigen-presenting cells and subsequently on tumor-specific T cells.…”

“…30 The contrasting results obtained by different groups seem to be related to the vaccination route, further encouraging the need of more comprehensive studies dissecting the signaling pathways activated in each particular tissue. 30 Indeed, a different situation can be observed within the tumor microenvironment, where activation of type I IFN-producing PRRs has been shown to promote potent anti-tumor effects by acting on antigen-presenting cells and subsequently on tumor-specific T cells. 31,32 Treatment of B16F10 melanoma tumors with poly(I:C) and CpG oligos, triggering TLR3 and 9 respectively, protected mice from tumor challenge together with melanoma specific T-cell transfer.…”

Potent therapeutic efficacy of an alphavirus replicon DNA vaccine expressing human papilloma virus E6 and E7 antigens

“…This observed inverse correlation between dose and immunogenicity of alphaviral DNA replicons is not unprecedented, as it has been previously observed in other studies with type I IFNs halting the production and amplification of the replicon due to their effect on cells undergoing an antiviral state. 8,18 This decreased immunogenicity was observed for both humoral and cellular immune responses. 18,34 Interestingly, upon assessment for frequencies of E7-specific T cells in blood, we hadn’t observed a significant difference between the different doses used.…”

“…Stimulation of PRR leads to a high production of type I interferon. 8,9 Likely the antigenicity of the replicase is also partly due to the expression of strong helper epitopes. Subsequent to the antigen production, apoptosis of the infected cells is induced leading to activation of dendritic cells resulting in CD8 + T cell responses.…”

Semliki Forest virus biodistribution in tumor-free and 4T1 mammary tumor-bearing mice: a comparison of transgene delivery by recombinant virus particles and naked RNA replicon

“…38 In addition to high expression levels of inserted gene provided by self-replicating RNA, the various RNAspecies produced by the replicon amplification initiates antiviral program resulting in type I interferon production and induction of apoptosis. 6,39 Therefore, the RNA-based vectors are potent immunostimulatory ligands providing excellent adjuvant properties and inducing strong cytopathic effect. As shown in previous studies, recRNA vectors have been used successfully for vaccine development through intramuscular injections.…”