Recombinant Semliki Forest virus particles expressing louping ill virus antigens induce a better protective response than plasmid-based DNA vaccines or an inactivated whole particle vaccine

Louping ill virus (LIV) infection of mice was used as a model to evaluate t he protective efficacy of Semliki Forest virus (SFV)-based vaccines in comp arison to a standard DNA vaccine and a commercial chemically inactivated va ccine. The recombinant SFV-based vaccines consisted of suicidal particles a nd a naked layered DNA/RNA construct. The nucleic acid vaccines expressed t he spike precursor prME and the nonstructural protein 1 (NS1) antigens of L IV. Three LIV strains of graded virulence for mice were used for challenge. One of these was a naturally occurring antibody escape variant, All vaccin es tested induced humoral immunity but gave varying levels of protection ag ainst lethal challenge. Only recombinant SFV particles administered twice g ave full protection against neuronal degeneration and encephalitis induced by two of the three challenge strains, and partial protection against the h ighly virulent strain, whereas the other vaccines tested gave lower levels of partial protection.