Effect of MOI ratio on the composition and yield of chimeric infectious bursal disease virus-like particles by baculovirus co-infection: deterministic predictions and experimental results

Virus-like particles (VLPs) are empty particles consisting of virus capsid proteins that closely resemble native virus but are devoid of the native viral nucleic acids and therefore have attracted significant attention as noninfectious vaccines. A recombinant baculovirus, vIBD-7, which encodes the structural proteins (VP2, VP3, and VP4) of infectious bursal disease virus (IBDV), produces native IBD VLPs in infected Spodoptera frugiperda insect cells. Another baculovirus, vEDLH-22, encodes VP2 that is fused with a histidine affinity-tag (VP2H) at the C-terminus. By co-infection with these two baculoviruses, hybrid VLPs with histidine tags were formed and purified by immobilized metal affinity chromatography (Hu et al., 1999). Also, we demonstrated that varying the MOI ratio of these infecting viruses altered the extent of VP2H incorporated into the particles. A dynamic mathematical model that described baculovirus infection and VLP synthesis (Hu and Bentley, 2000) was adapted here for co-infection and validated by immunofluorescence labeling. It was shown to predict the VLP composition as a dynamic function of MOI. A constraint in the VP2H content incorporated into the particles was predicted and shown by experiments. Also, the MOI ratio of both infecting viruses was shown to be the major factor influencing the composition of the hybrid particles and an important factor in determining the overall yield. ELISA results confirmed that VP2H was exhibited to a varied extent on the outer surface of the particles. This model provides insight on the use of virus co-infection in virus-mediated recombinant protein expression systems and aids in the optimization of chimeric VLP synthesis.