A high efficacy DNA vaccine against Tilapia lake virus in Nile tilapia (Oreochromis niloticus)

Tilapia lake virus (TiLV) is the main tilapia-infecting virus worldwide, causing serious economic losses to the tilapia aquaculture. However, there is no vaccine for this viral disease. Here, TiLV ORF10 (TiLV-ORF10) encoding a protein with abundant epitopes was cloned into the eukaryotic expression vector pcDNA3.1 as a vaccine candidate, and then used to evaluate the protective effects against TiLV in Nile tilapia (Oreochromis niloticus). RT-PCR and Western blot analyses confirmed pcDNA3.1–ORF10 expression in tilapia. The transcription levels of immunity-related genes such as immunoglobulin M, Toll-like receptor 2, myeloid differentiation factor 88, interleukin 8, tumor necrosis factor alpha, gamma-IFN, and nuclear factor κB were significantly upregulated in the spleen, liver, and kidney of the vaccinated tilapias (P < 0.05). TiLV challenge experiments showed that relative percent survival (RPS) was significantly enhanced in fish vaccinated with the DNA vaccine. Moreover, the RPS was significantly higher in fish vaccinated with a high dose of the DNA vaccine (85.72% RPS at a dosage of 45 μg DNA vaccine plasmid). Meanwhile, vaccination with pcDNA3.1–ORF10 significantly reduced virus replication, as evidenced by the lower amount of virus in the spleen, liver, and kidney of vaccinated tilapia than tilapias vaccinated with the empty pcDNA3.1 plasmid. Thus, pcDNA3.1–ORF10 could induce protective immunity in tilapia and may be a potential vaccine candidate for controlling disease caused by TiLV.