Humoral, mucosal, and cellular immune responses to oral Norwalk virus-like particles in volunteers

Norwalk virus-like particles (VLPs), made from recombinant capsid protein, are a promising vaccine. Thirty-six healthy adult volunteers received 250 μg (n = 10), 500 μg (n = 10), or 2000 μg (n = 10) of orally administered VLP or placebo (n = 6). All vaccinees developed significant rises in IgA anti-VLP antibody-secreting cells. Ninety percent who received 250 μg developed rises in serum anti-VLP IgG; neither the rates of seroconversion nor geometric mean titers increased at the higher doses. About 30–40% of volunteers developed mucosal anti-VLP IgA. Lymphoproliferative responses and IFN-γ production were observed transiently among those who received 250 μg or 500 μg but not 2000 μg of VLP. Studies to increase immunogenicity using a mucosal adjuvant are planned.