Double-Subgenomic Sindbis Virus Recombinants Expressing Immunogenic Proteins of Japanese Encephalitis Virus Induce Significant Protection in Mice against Lethal JEV Infection

A series of double-subgenomic Sindbis virus (dsSIN) recombinants that express cassettes encoding the immunogenic proteins of Japanese encephalitis virus (JEV) [prM-E, prM-E-NS1, NS1-NS2A, 80%E (encodes the amino-terminal 80% part of E), and NS1] were constructed and analyzed for their ability to confer protective immunity in mice against lethal challenge with neurovirulent JEV. The cassettes were introduced into both 5′ [second subgenomic promoter of the vector precedes the SIN structural open reading frame (SP-ORF)] and 3′ (the promoter follows the SP-ORF) dsSIN vectors, The longest cassette (prM-E-NS1) was 3.2 kb in length, which is remarkable for such a small vector virus as SIN (SIN genome is roughly 11.8 kb in length). The level of expression of JEV proteins appeared similar for both 5′ and 3′ recombinants. In general, the stability of the recombinants obtained was found to be low (expression was lost following one to five passages at low multiplicity of infection, depending on the recombinant). However, 5′ recombinants containing longer cassettes (prM-E-NS1, prM-E, NS1-NS2A) were more stable than the corresponding 3′ recombinants. Intraperitoneal inoculation of mice with 107 PFU of dsSIN-JEV recombinants induced antibodies against JEV proteins and low titers of JEV-neutralizing antibodies were produced by mice inoculated with recombinants expressing 80%E, prM-E, and prM-E-NS1. A single immunization of mice with the dsSIN-prM-E or dsSIN prM-E-NS1 recombinants provided 40-65% protection against peripheral lethal challenge with 104 LD50 of neurovirulent JEV. The results demonstrate that genetically engineered togaviruses can be successfully used as vaccine vectors.