Strategies and hurdles using DNA vaccines to fish

Abstract

DNA vaccinations against fish viral diseases as IHNV at commercial level in Canada against VHSV at experimental level are both success stories. DNA vaccination strategies against many other viral diseases have, however, not yet yielded sufficient results in terms of protection. There is an obvious need to combat many other viral diseases within aquaculture where inactivated vaccines fail. There are many explanations to why DNA vaccine strategies against other viral diseases fail to induce protective immune responses in fish. These obstacles include: 1) too low immunogenicity of the transgene, 2) too low expression of the transgene that is supposed to induce protection, 3) suboptimal immune responses, and 4) too high degradation rate of the delivered plasmid DNA. There are also uncertainties with regard distribution and degradation of DNA vaccines that may have implications for safety and regulatory requirements that need to be clarified. By combining plasmid DNA with different kind of adjuvants one can increase the immunogenicity of the transgene antigen – and perhaps increase the vaccine efficacy. By using molecular adjuvants with or without in combination with targeting assemblies one may expect different responses compared with naked DNA. This includes targeting of DNA vaccines to antigen presenting cells as a central factor in improving their potencies and efficacies by means of encapsulating the DNA vaccine in certain carriers systems that may increase transgene and MHC expression. This review will focus on DNA vaccine delivery, by the use of biodegradable PLGA particles as vehicles for plasmid DNA mainly in fish.

Development of Streptococcus agalactiae vaccines for tilapia

“…DNA vaccines and their effects against several viral and bacterial diseases in fish have been reported in the last decade (Hølvold et al 2014); however, only a few DNA vaccine strategies have been successful in providing significant protection to fish against S. agalactiae infection. Huang et al (2014) developed an oral DNA vaccine that encoded Sip.…”

DNA vaccines for fish: Review and perspectives on correlates of protection

“…As traditional oil‐based vaccines show similar efficacies as the bacterial DNA vaccines (Hølvold, Myhr, & Dalmo, ), the need for a bacterial DNA vaccine for fish is not as urgent as antiviral ones. Despite an enormous amount of effort invested in the development of DNA vaccines to protect veterinary animal species and humans against viruses, only a few have reached the market.…”

“…More than 20 different virus DNA vaccines have been developed experimentally for prophylactic use in fish targeting viruses such as rhabdoviridae, orthomyxoviridae, togaviridae and nodaviridae. The rhabdoviridae DNA vaccines (e.g., VHSV and IHNV) have shown high levels of efficacies, whereas others have in most instances possessed moderate to low efficacies (Hølvold et al., ; Munang'andu & Evensen, ).…”

DNA vaccine-mediated innate immune response triggered by PRRs in teleosts

“…In teleosts, PRR-associated sensing of exogenous nucleotides has been shown to lead to antiviral responses via the production of type I IFN and other cytokines. Hence, exogenous nucleic acids (i.e., DNA vaccines, viral RNA, and bacterial DNA) and their analogs can be used as vaccine adjuvants for aquaculture [43]. In this section, therefore, we summarize the nucleotide-sensing PRRs and their cascades in teleosts.…”