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Improving vaccination of carp against spring viraemia of carp virus (SVCV)

Final Report Summary - FISHVAC (Improving vaccination of carp against spring viraemia of carp virus (SVCV))

The overall objective of the project FISHVAC (Project No: 273391) was to investigate in fish the evolutionary conservation of the role of 'virus-induced interferons (IFNs)'. IFNs are cytokines; small proteins important for cell signalling which play a role in the communication between different white blood cells. IFNs in fish form a separate group (IFNφ) with a hypothesized function in adaptive immunity. We aimed to assess the potential for IFNφ to be used as molecular adjuvant (“helper substance”) in order to improve vaccination of common carp (Cyprinus carpio) against the infectious pathogen; Spring Viremia of Carp virus (SVCV).

The fish species and pathogen were not chosen randomly. Common carp is worldwide the most cultured fish species for food consumption (FAO, 2009) and koi (Cyprinus carpio koi) are ornamental varieties of common carp kept for decorative purposes as pet animals that are very valuable in some cases (individual fish may exceed €100.000). However, carp farming and large-scale transport of live koi for exhibition shows, often without health certification, has contributed to the rapid, worldwide spreading of deadly diseases such as Spring Viremia of Carp (SVC). This viral disease is classified as notifiable by the World Organisation for Animal Health (OIE), and diagnosis of SVC in fish farms may result in quarantine of the infected fish and depopulation.

Although sometimes particular anti-viral chemicals can help combat viral pathogens and diseases, these measures often cope with developing resistance in the targeted pathogens and with pollution of the environment. Our vaccination approach, aimed to be more sustainable, comprised 4 main research objectives. Briefly:

(1) All common carp IFNφ genes were identified and their regulation of gene expression during in vivo infection with SVCV described,
(2) The most upregulated IFNφ genes were cloned into a eukaryotic system suitable for transfection of cell lines with the aim to produce properly-folded recombinant IFNφ proteins in the supernatant,
(3) The activity of different recombinant IFNφ proteins was analyzed in vitro by measuring antiviral states of IFNφ-treated cells,
(4) We designed an experimental ‘IFNφ-adjuvated’ DNA vaccine (using the gene coding for the most immunogenic part of SVCV: the glycoprotein G, as core DNA vaccine) that, when used to protect against in vivo challenge with SVCV, provided higher levels of protection than control vaccines without the use of IFNφ as adjuvant.

For some of the above-mentioned objectives, several scientific challenges had to be overcome. For example, initial information in the database on carp IFNφs was incomplete or wrong. Collaboration with Leiden University (The Netherlands) led to publication of a first version of the common carp genome which helped us to correct and complete the initial information. Collaboration with the INRA institute in France helped to establish reliable bath challenge protocols of carp with SVCV. Further, in parallel to the main research objectives, we identified and characterized a large number of IFN-stimulated gene (ISG) members, belonging to several important ISG families, in the carp genome. This helped to evaluate biological activities of the recombinant IFNφs at early stages post-treatment. It was shown that induced ISG expression patterns could describe well the biological activity of the different fish IFNφs.

We significantly advanced the present knowledge on fish IFNφs by i) identifying new IFNφ members, ii) describing IFNφ gene expression patterns under normal conditions and during infection, iii) studying biological and antiviral activity of recombinant IFNφ proteins and iv) identifying and characterizing carp interferon-stimulated genes under normal conditions, during viral infection and in response to recombinant IFNφs. Thereby, we demonstrated the potential of IFNφs to be used as molecular adjuvants with the aim to increase the efficacy of current vaccines. These improved vaccines can help prevent infectious viral diseases of common carp. Although further molecular-immunological characterization would help explain further the underlying protective mechanisms, our data provide possibilities for implementation in aquaculture and ornamental fish trading industries. The growing aquaculture industry may benefit from future vaccine applications based on our data, while preserving the environment. Thereby, our results may contribute to a mitigation of economic losses associated with severe outbreaks of lethal viral infectious diseases of fish in aquaculture.