Altered host immune responses following infection with miR-150 expressing influenza viruses

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Abstract Current influenza vaccines offer considerable protection for the majority of the population. However, vaccine efficacy amongst high risk populations, such as the elderly, is variable. Novel approaches are therefore required to improve vaccine efficiency in these susceptible populations. MicroRNAs (miRNAs) play important roles in the regulation of immune responses by modulating gene expression. Our work describes the generation and delivery of engineered influenza viruses with the ability to express defined immunomodulatory miRNAs. MicroRNA-150 (miR-150) has been shown to be involved in the development of T cell and B cell. Furthermore, evidence suggests that circulating miR-150 can be actively transported to target cells where it can influence gene expression. In this study, we first investigated the ability of recombinant influenza viruses to deliver immunomodulatory miR-150, and alter cytokine production in vitro. miR-150 was inserted into an artificial intron between the NS1 and NEP genes of the PR8 H1N1(PR8-150) and X31 H3N2 (X31-150) influenza A viruses and was rescued using reverse genetics. Mature miR-150 expression was confirmed using qPCR and by knockdown of its target gene, c-Myb, using a dual-luciferase assay. Moreover, cytokine mRNA expression levels (IL-6, IFN-β, CXCL10 and CCL5) were enhanced following infection with PR8-150 in A549 cells. Mice infected intranasally with recombinant X31-150 virus showed significantly higher numbers of neutrophils, macrophages and influenza specific CD8+ T cells post infection compared to X31 wild type controls. These results demonstrate that recombinant influenza viruses can be used to deliver functional miRNAs with the ability to modulate immunity both in vitro and in vivo.