Recombinant Norwalk virus-like particles as an oral vaccine

Viruses that infect cells in the gastrointestinal tract are well suited for examining the immune response to oral delivery of antigen and for exploring the advantages and pitfalls of oral vaccines. Norwalk virus (NV) (family Caliciviridae, genus Calicivirus) causes acute gastroenteritis in all age groups. The NV capsid is composed of 180 copies of a single 58000 molecular weight protein which spontaneously forms virus-like particles (VLPs) that can be purified in extremely high yields (22 mg per 300 ml culture) when produced using the baculovirus expression system. We are testing the potential of these recombinant NV (rNV) particles for use as an oral vaccine by administering them to mice and volunteers. Mice were orally inoculated four times with rNV particles in concentrations ranging from 5 to 500 micrograms in the absence of adjuvant or from 5 to 200 micrograms with 10 micrograms of cholera toxin. Serum IgG and fecal IgA immune responses were monitored. rNV particles were found to be immunogenic when orally given to mice with or without adjuvant. These particles also were safe and immunogenic when orally given to volunteers. These studies show that rNV particles are an excellent model to test the oral delivery of mucosal immunogens in general, and that rNV particles are ideal candidates for vaccine development in particular.