Peptide nanoparticles as novel immunogens: design and analysis of a prototypic severe acute respiratory syndrome vaccine.

Severe acute respiratory syndrome (SARS) is an infectious disease caused by a novel coronavirus that cost nearly 800 lives. While there have been no recent outbreaks of the disease, the threat remains as SARS coronavirus (SARS-CoV) like strains still exist in animal reservoirs. Therefore, the development of a vaccine against SARS is in grave need. Here, we have designed and produced a prototypic SARS vaccine: a self-assembling polypeptide nanoparticle that repetitively displays a SARS B-cell epitope from the C-terminal heptad repeat of the virus' spike protein. Biophysical analyses with circular dichroism, transmission electron microscopy and dynamic light scattering confirmed the computational design showing alpha-helcial nanoparticles with sizes of about 25 nm. Immunization experiments with no adjuvants were performed with BALB/c mice. An investigation of the binding properties of the elicited antibodies showed that they were highly conformation specific for the coiled-coil epitope because they specifically recognized the native trimeric conformation of C-terminal heptad repeat region. Consequently, the antisera exhibited neutralization activity in an in vitro infection inhibition assay. We conclude that these peptide nanoparticles represent a promising platform for vaccine design, in particular for diseases that are characterized by neutralizing epitopes with coiled-coil conformation such as SARS-CoV or other enveloped viruses.