Abstract
Vaccines based on virus-like particles (VLPs) have proven effective in humans and animals. In this regard, the baculovirus expression vector system (BEVS) is one of the technologies of choice to generate such highly immunogenic vaccines. The extended use of these vaccines for human and animal populations is constrained because of high production costs, therefore a significant improvement in productivity is crucial to ensure their commercial viability. Here we describe the use of the previously described baculovirus expression cassette, called TB, to model the production of two VLP-forming vaccine antigens in insect cells. Capsid proteins from porcine circovirus type 2 (PCV2 Cap) and from the calicivirus that causes rabbit hemorrhagic disease (RHDV VP60) were expressed in insect cells using baculoviruses genetically engineered with the TB expression cassette. Productivity was compared to that obtained using standard counterpart vectors expressing the same proteins under the control of the polyhedrin promoter. Our results demonstrate that the use of the TB expression cassette increased the production yields of these vaccine antigens by around 300% with respect to the standard vectors. The recombinant proteins produced by TB-modified vectors were fully functional, forming VLPs identical in size and shape to those generated by the standard baculoviruses, as determined by electron microscopy analysis. The use of the TB expression cassette implies a simple modification of the baculovirus vectors that significantly improves the cost efficiency of VLP-based vaccine production, thereby facilitating the commercial viability and broad application of these vaccines for human and animal health.
Highlights
Recent decades have witnessed the growing use of baculovirus vectors to produce and obtain a range of recombinant proteins [1,2]
The purpose of this study is to demonstrate the efficiency of TB-modified baculoviruses to produce virus-like particles (VLPs) using as models the Porcine circovirus 2 (PCV2) and rabbit hemorrhagic disease virus (RHDV) capsid proteins
The expression of PCV2-Cap protein induced by the TB(-) baculovirus was initially detected by Coomassie blue staining at 48 hpi and presented a peak of maximum productivity at this time, as determined by Western blot (Fig 2A)
Summary
Recent decades have witnessed the growing use of baculovirus vectors to produce and obtain a range of recombinant proteins [1,2]. Since the development of the baculovirus expression vector system (BEVS) in the ‘80s [3], thousands of recombinant proteins, ranging from cytosolic enzymes to membrane-bound proteins, have been successfully produced in baculovirus-infected insect cells. A baculovirus vector expression cassette containing rearranged baculovirusderived genetic regulatory elements acting in cascade has been described [4]. This novel cassette, denominated TB, conferred significant production improvements to the BEVS, including prolonged cell integrity after infection, improved protein integrity, and up to a 4-fold increase in the production yield of a recombinant model protein (green fluorescent protein) with respect to a standard baculovirus vector. The expression cassette consists of a cDNA encoding for the baculovirus transactivation factors IE1 and IE0, expressed under the control of the polyhedrin (polh) promoter, and a homologous repeated transcription enhancer sequence operatively cis-linked to p10 chimeric promoters
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