Production and purification of immunogenic virus-like particles formed by the chimeric infectious bursal disease virus structural protein, rVP2H, in insect larvae

Abstract

This study describes an alternative approach to produce rVP2H protein using insect larvae of the cabbage looper Trichoplusia ni as hosts for the expression of the protein. The chimeric rVP2H protein, having an extra six histidine residues at the C-terminus of the VP2, a structural protein of infectious bursal disease virus (IBDV), is a vaccine candidate for the prevention of infectious bursal disease. The chimeric rVP2H protein was expressed in insect larvae in form of virus-like particles, in which they maintain their native immunogenic properties. The expression level of rVP2H protein in T ni larvae was estimated to be approximately 0.4 mg/g of larvae or 0.2 mg/larvae. The rVP2H particles have a uniform morphology of dodecahedral structure with a size of 23 nm in diameter, and the particles could be affinity-purified in one step with immobilized metal-ion affinity chromatography (IMAC) from the larvae homogenate. The recovery of rVP2H protein was approximately 55% following IMAC and the protein was obtained with a purity of around 90%. An additional purification step of ammonium sulphate precipitation was added to speed up the process of microfiltration and ultrafiltration of the homogenate prior to IMAC. This step enhanced the final purity of rVP2H protein to 99%, demonstrating that the purification protocol developed herein was a powerful strategy for obtaining highly pure rVP2H protein from insect larvae. The immunogenicity and protective properties of the larvae-derived rVP2H protein were evaluated using a chicken protection assay. When larvae-derived rVP2H protein was intramuscularly injected into specific-pathogen-free chickens (20 mug/bird), high titres of virus-neutralizing antibodies were induced and the chickens were protected from the infection of a very virulent strain of IBDV isolated locally. (C) 2003 Elsevier Ltd. All rights reserved.