Characterization of a recombinant Sendai virus vector encoding the small ruminant lentivirus gag-P25: antiviral properties in vitro and transgene expression in sheep

Small ruminant lentiviruses (SRLV) cause multisystemic chronic inflammatory disease and significant economic losses in sheep and goats worldwide. However, no vaccines or therapies are currently available. In this study, a recombinant Sendai virus (SeV) vector encoding the SRLV gag-P25 gene (rSeV-GFP-P25) from the EV1 strain was generated using In-FUSION cloning and rescued using the SeV reverse genetic system. Transgene expression and stimulation of innate immunity and interferon-stimulated genes (ovine A3Z1, OBST2 and SAMHD1) were evaluated in ovine skin fibroblasts (OSF) transduced with SeV-GFP and rSeV-GFP-P25. Additionally, to characterize the effect of the SRLV restriction in transduced OSF, the SRLV DNA load was quantified at different times post-transduction and post-infection with strain EV1. Using immunohistochemistry and image analysis, transgene expression and tissue distribution of recombinant P25 were studied in two lambs inoculated intranasally, one with rSeV-GFP-P25 and the other with SeV-GFP. rSeV-GFP-P25 induced efficient and transient transgene expression in vitro and in vivo. Furthermore, OSF transduced with rSeV-GFP-P25 presented upregulation of TLR2, TLR3, TLR6, TLR7, RIG-I, MyD88 and IFN-β, whereas SeV-GFP did not induce TLR6 or IFN-β upregulation. Among the interferon-stimulated genes, OBST2 was significantly upregulated after transduction with rSeV-GFP-P25 compared with the empty vector. SRLV restriction gradually increased and persisted after transduction with SeV-GFP and rSeV-GFP-P25, with OSF transduced three times showing cumulative restriction. Forty-eight hours post-inoculation in vivo, marked P25 expression was observed in ciliated epithelial cells and submucosal macrophages/dendritic cells of the nasal mucosa. This study reinforces the important role of the innate immune response in controlling SRLV infection and suggests that rSeV-GFP-P25 is a potential vaccine candidate against SRLV.