DEVELOPMENT OF DNA VACCINES FOR FISH - VECTOR DESIGN, INTRAMUSCULAR INJECTION AND ANTIGEN EXPRESSION USING VIRAL HEMORRHAGIC SEPTICEMIA VIRUS GENES AS MODEL

Disease control is one of the major concerns in the aquaculture indust ry. However, there are no vaccines available for the prevention of man y piscine infectious diseases, especially those of viral and parasitic origin. DNA-based vaccination could circumvent several problems assoc iated with traditional methods of immunization, but little is known on its efficacy in fish. The luciferase and lacZ reporter genes were use d to characterize expression of plasmid-encoded genes in rainbow trout and zebra fish injected intramuscularly. For a given dose of DNA, the luciferase activity was higher in fish than in mouse muscle. The enzy me activity in fish peaked with 1 mu g of DNA and remained constant fo r over 12 weeks, but it was not limited to the injected muscle since l uciferase activity was also detected in the gills. Thin sections of ra inbow trout muscle injected with the lacZ reporter gene showed no perm anent tissue damage. To further investigate the ability of DNA-based v accines to induce protective immunity in fish, viral haemorrhagic sept icaemia virus G and N genes were cloned individually into an expressio n plasmid. Both G and N proteins produced in transfected fish cells ap peared identical to native viral proteins, as they were recognized by specific monoclonal antibodies. Coinjection of the G and luciferase ge nes in fish muscle resulted in a rapid decrease of the luciferase acti vity over time, when compared to the control, suggesting that fish rai sed a cellular immune response to the G protein, killing the transfect ed host cells and ablating further expression of CT protein and lucife rase. Finally, young rainbow trout injected with the G construct, alon e or together with the N construct, were strongly protected against ch allenge with live virus. These results suggest that DNA vaccines shoul d be as successful for fish as they are for other animals. (C) 1998 Ac ademic Press Limited.