Recombinant channel catfish virus (Ictalurid herpesvirus 1) can express foreign genes and induce antibody production against the gene product

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AbstractThe potential use of channel catfish virus (CCV) (Ictalurid herpesvirus 1) as a vaccine vector for the channel catfish industry was investigated by inserting the Escherichia coli lacZ gene into the CCV genome and evaluating the immune response to the foreign gene product in catfish exposed to the recombinant. The recombinant virus was produced by inserting the lacZ in reading frame with the ATG start codon of the CCV thymidine kinase (TK) gene in the recombinant transfer plasmid pBSCV457 described previously. The plasmid was then cotransfected with CCV DNA in a TK gene‐mediated selectable homologous recombination. The recombinant progeny were selected by resistance to 0.1 mM acycloguanosine (acyclovir) and the production of blue plaques in the presence of 5‐bromo‐4‐chloro‐3‐indolyl‐β‐D‐galactopyranoside (X‐gal). The resultant construct (CCVlacZ) was TK−, and contained the lacZ gene at both TK loci in the genome. β‐Galactosidase expression in infected CCO ceils reached 0.53 μg per 106 CCO cells at 12 h post‐infection. When channel catfish fingerlings were immersion exposed to CCVlacZ, these developed an antibody response to the inserted foreign gene product which peaked at approximately 15–20 days post‐infection. Additionally, the anti‐β‐galactosidase response was significantly enhanced when the fingerlings were re‐exposed to the virus 20 days after the initial exposure. These results demonstrate that foreign genes can be inserted into and expressed by CCV and that such constructs could be used as vaccine vectors.