Use of an outbred rat hepacivirus challenge model for design and evaluation of efficacy of different immunisation strategies for HCV.

The lack of immunocompetent small animal models for hepatitis C virus (HCV) has greatly hindered the development of effective vaccines. Using rodent hepacivirus (RHV), a homologue of HCV that shares many characteristics of HCV infection, we report the development and application of a novel RHV/ outbred rat model for HCV vaccine development. Simian adenovirus (ChAdOx1) encoding a genetic immune enhancer (truncated shark class II invariant chain) fused to the non-structural proteins NS3-NS5B from RHV (ChAd-NS) was used to vaccinate Sprague-Dawley rats, resulting in high levels of CD8+ T-cell responses. Following RHV challenge (using 10x or 100x the minimum infectious dose), 42% of vaccinated rats cleared infection within 6-8 weeks, while all mock vaccinated controls became infected with high level viraemia post-challenge. A single, 7-fold higher dose of ChAd-NS increased efficacy to 67%. Boosting with ChAd-NS, or with a plasmid encoding the same NS3-NS5B antigens, increased efficacy to 100% and 83% respectively. A ChAdOx1 vector encoding structural antigens (ChAd-S) was also constructed. ChAd-S alone showed no efficacy. Strikingly, when combined with ChAd-NS, ChAD-S produced 83% efficacy. Protection was associated with a strong CD8+ IFNγ+ recall response against NS4. Next-generation sequencing of a putative RHV escape mutant in a vaccinated rat identified mutations in both of two identified immunodominant CD8+ T-cell epitopes. CONCLUSIONS: A simian adenovirus vector vaccine strategy is effective at inducing complete protective immunity in the rat/RHV model. The RHV SD rat challenge model enables comparative testing of vaccine platforms and antigens, identification of correlates of protection and thereby provides a small animal experimental framework to guide the development of an effective vaccine for HCV in humans. This article is protected by copyright. All rights reserved.