RECOMBINANT NORWALK VIRUS-LIKE PARTICLES ADMINISTERED BY THE ORAL OR INTRANASAL ROUTE ARE IMMUNOGENIC IN BALB-C MICE

Abstract

Norwalk virus (NV) is a major cause of outbreaks of acute nonbacterial gastroenteritis in the United States. The second open reading frame encodes the capsid protein that self assembles to form empty virus-like particles (VLPs) similar to native Norwalk virions in size and appearance. We evaluated the immunogenicity of recombinant Norwalk virus-like particles (rNV VLPs) when administered to mice by oral or intranasal (IN) routes, and tested if the response is enhanced by co-administration of a mucosal adjuvant. METHOD: Groups of 6 BALB-c mice were immunized by the oral or IN route. Immunizations were performed twice at a 3 week interval in the presence or absence of a mucosal adjuvant, Escherichia coli labile toxin (LT) or a mutant labile toxin, LT(R192G) [from JD Clements (Tulane Univ. Med. Center)]. Serum and fecal samples were collected at 0, 14, and 35 days post immunization. ELISA was used to determine rNV-specific serum IgG and intestinal IgA antibody titers. RESULTS: Following the IN administration of 10 or 25μg of rNV VLPs, 100% of the mice had a rNV specific serum IgG response with geometric mean titers (GMTs) of 10,240 and 5,747, respectively. Co-administration of LT or LT (R192G) enhanced the serum IgG response (GMTs of 163,840 and 292,929,respectively). After the oral administration of 200 μg of rNV VLPs, 100% of the mice had rNV specific serum IgG antibody (GMT of 1,470). Following the IN administration of 10 or 25 μg rNV VLPs, 83% and 100% of the mice had rNV-specific intestinal IgA response (GMTs of 36 and 296, respectively). Co-administration of LT (R192G) or LT enhanced the intestinal IgA (GMTs of 849 and 855, respectively). After the oral administration of 200μg of rNV VLPs, 60% of the mice had rNV-specific IgA response (GMT of 27). CONCLUSION: The IN delivery of rNV VLPs is more effective than the oral route at inducing serum IgG and intestinal IgA responses to low dose of rNV particles. The rNV VLPs are immunogenic when delivered mucosally to mice, and are a potential vaccine for humans.