A single dosis of a suicidal DNA vaccine develops specifical immune response in salmonids

Abstract

Heterologous gene expression by Semliki Forest Virus (SFV) replicon vector was investigated for the development of an effective DNA fish vaccine. The Escherichia coli LacZ (β-galactosidase) gene, was cloned into a DNA plasmid vector that contained the alphavirus replicon under the control of a Cytomegalovirus (CMV) promoter and the appropriate polyadenylation signal [poly(A)] sequence. The resultant plasmid, pSFV-LacZ, was transfected into BHK-21 cells and the reporter gene expression was confirmed by X-gal staining , β-Galactosidase (β-Gal) enzyme assay and Western blot. In vivo studies in a rainbow trout maintained at 15C showed that one intramuscular immunization with 100 µg pSFV-LacZ induced a strong specific β-Gal antibody response, detected by Elisa test after 45 days post-vaccination. Our results show that a suicidal DNA immunogen can induce a specific response in fishes under commercial aquaculture conditions and suggest that SFV replicons as promising candidates as genetic vaccines in farm salmonids.