Single dose VSV-based vaccine protects mice against lethal heterologous Crimean-Congo hemorrhagic fever virus challenge

Crimean-Congo hemorrhagic fever virus (CCHFV) causes a severe, sometimes fatal hemorrhagic fever (CCHF) in humans. Currently, there are no approved therapies against CCHF. In this study we used the recombinant vesicular stomatitis virus (VSV) platform to generate live-attenuated recombinant CCHF vaccine candidates expressing the CCHFV nucleoprotein (NP) and glycoprotein precursor (GPC). As one approach, we utilized the established VSV expressing the full-length Ebola virus glycoprotein (VSV-EBOV) or a truncated version of the EBOV glycoprotein and added the CCHFV-NP (VSV-CCHFnp1 or VSV-CCHFnp2, respectively). Additionally, we prepared a vaccine candidate, VSV-CCHFgpc, in which the VSV glycoprotein was replaced with the CCHFV-GPC. Vaccine constructs induced CCHFV-specific IgG antibodies comprising largely IgG2c subclass. Only, the VSV-CCHFgpc vaccine candidate induced significant T cell immune responses directed against epitopes in the CCHFV-NSm and Gc proteins. Efficacy of the vaccine candidates was evaluated using a prime-only approach in a transiently immune-suppressed mouse model. Animals vaccinated with VSV-CCHFnp2 succumbed to lethal CCHFV challenge, while the VSV-CCHFgpc vaccine candidate afforded partial protection. In contrast, vaccination with VSV-CCHFnp1 uniformly protected animals against death. Our results demonstrate the promise of VSV-CCHFnp1 as a vaccine candidate for CCHFV and warrant continued development.