Chimpanzees as an animal model for human norovirus infection and vaccine development

Abstract

Noroviruses are global agents of acute gastroenteritis, but the development of control strategies has been hampered by the absence of a robust animal model. Studies in chimpanzees have played a key role in the characterization of several fastidious hepatitis viruses, and we investigated the feasibility of such studies for the noroviruses. Seronegative chimpanzees inoculated i.v. with the human norovirus strain Norwalk virus (NV) did not show clinical signs of gastroenteritis, but the onset and duration of virus shedding in stool and serum antibody responses were similar to that observed in humans. NV RNA was detected in intestinal and liver biopsies concurrent with the detection of viral shedding in stool, and NV antigen expression was observed in cells of the small intestinal lamina propria. Two infected chimpanzees rechallenged 4, 10, or 24 mo later with NV were resistant to reinfection, and the presence of NV-specific serum antibodies correlated with protection. We evaluated the immunogenicity and efficacy of virus-like particles (VLPs) derived from NV (genogroup I, GI) and MD145 (genogroup II, GII) noroviruses as vaccines. Chimpanzees vaccinated intramuscularly with GI VLPs were protected from NV infection when challenged 2 and 18 mo after vaccination, whereas chimpanzees that received GII VLPs vaccine or a placebo were not. This study establishes the chimpanzee as a viable animal model for the study of norovirus replication and immunity, and shows that NV VLP vaccines could induce protective homologous immunity even after extended periods of time.

Fig. 1.

Norwalk virus infection in chimpanzee A2A014. (A) Serum antibody isotype titers in chimpanzee A2A014. Titer of IgG, IgM, and IgA anti-NV (Right y axis) developed after NV virus infection, compared with norovirus shedding in stools (Left y axis). (B) Norovirus genome copies in biopsy samples from chimpanzee A2A014. The genome copies per 100 ng of total RNA in endoscope (duodenum, 11 dpi; jejunum, 21 dpi) and liver (7, 14, and 21 dpi) biopsies are shown in relationship to the titer of norovirus shedding in stools.

Fig. 2.

Immunohistochemistry of biopsy samples of duodenum and jejunum in chimpanzee A3A008. Preinoculation and 4-dpi endoscopic biopsies were incubated with a monoclonal anti-NV antibody labeled with FITC (green). Cell nuclei are shown with DAPI staining (blue). White arrows indicate representative NV-positive cells at 400×.

Fig. 3.

Detection of HBGA blocking antibodies in sera from vaccinated chimpanzees. Sera from NV (GI) and MD145 (GII) vaccinated chimpanzees before and 60 dpv were tested for the ability to block the interaction between recombinant NV VLPs and H3 carbohydrates. A chimpanzee that was administered placebo was included as a control. The difference in BT50 (blocking titer 50%) between 60-dpv NV-vaccinated and MD145-vaccinated chimpanzees was significant (***P < 0.001).