A Severe Acute Respiratory Syndrome (SARS) pandemic, caused by re-emergence of the causative coronavirus (CoV) from an animal reservoir, is a serious threat. Induction of protective antibody by vaccination has proven the most effective intervention for highly contagious viral pathogens. The capsid proteins of viruses typically self-assemble into empty capsids known as virus-like particles (VLPs). VLPs resemble native virions immunologically. As vaccine candidates, VLPs have the advantage of being non-replicating and non-pathogenic, and of presenting host protective epitopes in a particulate and multimeric form. We have generated SARS-CoV VLPs by expression of the spike (S), membrane (M) and small envelope (E) proteins in the baculovirus/insect cell system and shown that VLP are immunogenic in rabbits. We now propose: (1) to develop efficient methods for production of highly purified SARS-CoV M+E and M+E+S VLPs from insect cell cultures, (2) to characterize the immunogenicity of SARS-CoV VLP vaccines in BALB/c mice;and (3) to determine the potency of a VLP vaccine to protect BALB/c mice and ferrets challenged with live SARS-CoV. Recent studies have shown that amino acids changes in S can mediate increased resistance to neutralization and enhancement of S pseudotype virus entry. The conserved C terminus of coronaviruses contains epitopes that contribute to enhancement. Thus, our final specific aim (4) is to determine the cross neutralizing/enhancing capacity of antisera raised in mice against VLPs of SARS-CoV strains and the human coronaviruses, OC43 and 229E. The successful implementation of the proposed studies would provide a stepping-stone toward future clinical trials with a VLP-based SARS-CoV vaccine.
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