Blockade Antibody Responses in Human Subjects Challenged with a New Snow Mountain Virus Inoculum

Noroviruses (NoVs) are a leading cause of non-bacterial gastroenteritis in young children and adults worldwide. Snow Mountain Virus (SMV) is the prototype of NoV GII genotype 2 (GII.2) that has been developed as a viral model for human challenge studies, an important tool for studying pathogenesis and immune response of NoV infections and for evaluating NoV vaccine candidates. Previous studies have identified blockade antibodies that block the binding of NoV virus-like particles (VLPs) to histo-blood group antigens (HBGAs) as a surrogate for neutralization in human Norwalk virus and GII.4 infections but little is known about SMV blockade antibodies.

In this secondary data analysis study, blockade antibodies were characterized in pre-challenge and post-challenge serum samples from human subjects challenged with a new SMV inoculum. The correlation between blockade antibody geometric mean antibody titers (GMTs) and SMV-specific serum IgG/IgA GMTs were examined after stratifying the subjects by infection status. A linear mixed model was applied to test the association between HBGA blockade antibody concentrations and post-challenge days accounting for covariates and random effects.

Laboratory results from 33 SMV inoculated individuals were analyzed and 75.7% (25/33) participants became infected. Serum SMV-specific blockade antibodies, IgA, and IgG were all significantly different between infected and uninfected individuals beginning day 15 post-challenge. Within infected individuals, a significant correlation was observed between both IgG and IgA and blockade antibody concentration as early as day 6 post-challenge. Analysis of blockade antibody using the linear mixed model showed that infected individuals, when compared to uninfected individuals, had a statistically significant increase in blockade antibody concentrations across the post-challenge days. Among the post-challenge days, blockade antibody concentrations on days 15, 30, and 45 were significantly higher than those observed pre-challenge. The intraclass correlation coefficient (ICC) analysis indicated that the variability of blockade antibody titers is more observed between individuals rather than within subjects.

These results indicate that HBGA-blockade antibody GMTs are generated after SMV challenge and the blockade antibodies were still detectable at day 45 post-challenge. These data indicate that the second-generation of SMV inoculum is highly effective.