In-Vitro and In-Vivo Recombinant Expression of Tilapia Lake Virus S4 Protein Using Extended Host-Range Baculovirus Expression Vector and Generation of Polyclonal Anti-S4 Antibodies

The global tilapia industry is threatened due to the mass die-off of farmed tilapia caused by an emerging virus, Tilapia Lake Virus (TiLV). The threat of TiLV disease demands for cost-effective diagnostics and preventive measures such as protein and antibody-based detection tools and even vaccines like protein subunit vaccines. In this study, we aimed to recombinantly express the entire S4 protein of TiLV in vitro and in vivo using an extended host-range baculovirus expression vector system (EHR-BEVS) and used the purified protein to generate polyclonal anti-S4 antibodies. The parental extended host-range ABM-eIF4E baculovirus previously developed in our laboratory was used to generate the recombinant ABM-eIF4E-S4-His baculovirus expression vector using homologous recombination and was purified through multiple rounds of plaque selection and end-point titration, eliminating the need for the use of antibiotic resistance gene selection marker. Different insect cell lines including Trichoplusia ni Hübner, 1802 larvae were infected with ABM-eIF4-S4-His to produce recombinant S4 protein. Western blotting was used to detect the recombinantly expressed S4 protein. We generated an antibiotic resistance gene-free EHR-BEV and observed the permissibility of all the insect cell lines tested including T. ni larvae to infection with the recombinant ABM-eIF4E-S4-His. Secondly, immunogenic S4 protein capable of eliciting rabbit polyclonal anti-S4 antibodies was recombinantly expressed in the infected insect cells and larvae. TiLV S4 protein was recombinantly expressed in vitro and in vivo using extended host-range ABM-eIF4E-S4-His baculovirus expression vector and was shown to induce rabbit antibody production that can recognize S4 protein supporting the potential of insect larvae as alternative biofactories in the production of recombinant TiLV protein subunit for the development of diagnostics and preventive vaccines against TiLV disease.