Potential use of chitosan nanoparticles for oral delivery of DNA vaccine in Asian sea bass (Lates calcarifer) to protect from Vibrio (Listonella) anguillarum

In recent years, attention has been focused on the possibility of utilizing DNA vaccines in fish aquaculture. A successful regime for intramuscular injection of naked DNA into fish has been developed and novel methods to deliver this DNA to fish are under investigation. The potential of chitosan as a polycationic gene carrier for oral administration has been explored since 1990s. The present study examines the potential efficacy of DNA vaccine against Vibrio anguillarum through oral route using chitosan nanoparticles encapsulation. The porin gene of V. anguillarum was used to construct DNA vaccine using pcDNA 3.1, a eukaryotic expression vector and the construct was named as pVAOMP38. The chitosan nanoparticles were used to deliver the constructed plasmid. In vitro and in vivo expression of porin gene was observed in sea bass kidney cell line (SISK) and in fish, respectively by fluorescent microscopy. The cytotoxicity of chitosan encapsulated DNA vaccine construct was analyzed by MTT assay and it was found that the cytotoxicity of pVAOMP38/chitosan was quite low. Distribution of gene in different tissues was studied in fish fed with the DNA (pVAOMP38) encapsulated in chitosan by using immunohistochemistry. The results indicate that DNA vaccine can be easily delivered into fish by feeding with chitosan nanoparticles. After oral vaccination Asian sea bass were challenged with Vibrio anguillarum by intramuscular injection. A relative percent survival (RPS) rate of 46% was recorded. The results indicate that Sea bass (Lates calcarifer) orally vaccinated with chitosan-DNA (pVAOMP38) complex showed moderate protection against experimental V. anguillarum infection.