DNA vaccination against channel catfish virus results in minimal immune response and is not efficacious against challenge

We evaluated DNA vaccination against channel catfish virus (CCV) by comparing 11 encoded genes, multiple doses, codelivery of DNA vaccines, and the resultant immune responses, as well as making a direct comparison with previously published DNA vaccines for CCV. The genes selected included immediate early genes, membrane genes, the major capsid gene, and the putative major envelope glycoprotein gene. The open reading frame (ORF) for each gene was amplified by using the polymerase chain reaction, cloned into pcDNA3.1/V5/His-TOPO, and expression of the predicted molecular weight proteins was confirmed in cell culture. Each vaccine was injected intramuscularly in doses of 50, 25, 5, or 1 μg and evaluated by immersion challenge. Detection of mRNA specific for ORF 59 and ORF 6 at the injection site indicated that the DNA vaccines were transcriptionally active in situ. Serum-neutralizing titers, enzyme-linked immunosorbant assay (ELISA) antibody titers, and Mx transcription were measured in response to vaccination. Significant protection was not observed in any experiment, including groups receiving multiple constructs. Published DNA vaccines encoding one of the outer membrane protein genes and the putative major envelope glycoprotein gene also failed to protect against disease in direct comparison with those constructed here, singly or in combination. Serum-neutralizing and ELISA antibody titers were generally low and not significantly different between groups. Mx transcription was induced in response to vaccination with both single and multiple DNA constructs. Although both innate and adaptive immune responses were detected in response to DNA vaccination for CCV, vaccination was not protective for any of the constructs tested. © Copyright by the American Fisheries Society 2005