Recombinant canine parvovirus-like particles express foreign epitopes in silkworm pupae

The capsid structural protein VP2 of canine parvovirus (CPV) can self-assemble into highly organized virus-like particles (VLPs) and retain major immunoreactivity. In this study, different recombinant baculoviruses that expressed varying fusion proteins of the CPV VP2 protein with the T cell determinant and/or the linear virus-neutralizing epitope of rabies virus (RV) were generated. Infection with these baculoviruses changed BmN cell morphology and inhibited their proliferation as well as damaged silkworms and pupae. However, infection with these baculoviruses induced high levels of recombinant protein expression in silkworms and pupae. More importantly, these fusion proteins self-assembled VLPs with properties similar to CPV virions and retained their VP2-specific immunoreactivity, but some retained their RV-specific immunoreactivity. Interestingly, only one fusion protein, T-VP2, maintained its haemagglutination activity. These data indicated that these insertions and replacements in the loop 2 of VP2 did not interfere with the formation of VLP, and silkworms and pupae could act as a low-costing bioreactor for the production of heterologous proteins. Therefore, our findings may provide a new framework for the development of subunit vaccines against RV and CPV.