Chimeric virus-like particles of human norovirus constructed by structure-guided epitope grafting elicit cross-reactive immunity against both GI.1 and GII.4 genotypes.

Human norovirus (HuNoV) is the main cause of acute non-bacterial gastroenteritis worldwide. There is no vaccine currently available to prevent HuNoV infection. HuNoV is a highly mutated virus, and its genetic diversity and the lack of cross-protection between different genotypes hinder the broadly protective vaccine development. Among various genotypes, GI.1 is the prototype strain, and GII.4 currently predominates the prevalence of HuNoV. In this work, guided by the structural alignment of GI.1 and GII.4 HuNoV capsid proteins, several chimeric virus-like particles (VLPs) were designed to achieve cross-immunity against these two HuNoV genotypes. The neutralizing epitopes of HuNoV have been identified to be mainly located at the loop regions of VP1 protein exposed on the HuNoV surface. In this study, the exposed loops of GII.4 VP1 protein were grafted into the scaffold of GI.1 genotype to produce the chimeric VLPs. The designed chimeric VLPs were recombinantly expressed by the Hansenula polymorpha expression system developed by our laboratory. Mice were immunized with the chimeric VLPs plus aluminum adjuvant, and then the antibody responses were detected by using the enzyme-linked immunosorbent assay and the histo-blood group antigen-VLP interaction blocking assay. The experimental results show that two of the designed chimeric VLPs induced cross-reactive IgG and cross-blocking antibodies against both the parental GI.1 and GII.4 genotypes of HuNoV. The results also imply that the transplant site design is important to maintain the immunogenicity of foreign epitopes on the scaffold carrier. Our studies may provide a valuable strategy for the development of cross-reactive HuNoV vaccines. IMPORTANCE Human norovirus (HuNoV) is highly infectious and can result in severe illnesses in the elderly and children. So far, there is no effective antiviral drug to treat HuNoV infection, and thus, the development of HuNoV vaccines is urgent. However, NoV evolves rapidly, and currently, at least 10 genogroups with numerous genotypes have been found. The genetic diversity of NoV and the lack of cross-protection between different genotypes pose challenges to the development of broadly protective vaccines. In this study, guided by structural alignment between GI.1 and GII.4 HuNoV VP1 proteins, several chimeric-type virus-like particles (VLPs) were designed through surface-exposed loop grafting. Mouse immunization studies show that two of the designed chimeric VLPs induced cross-immunity against both GI.1 and GII.4 HuNoVs. To our knowledge, this is the first designed chimeric VLPs that can induce cross-immune activities across different genogroups of HuNoV, which provides valuable strategies for the development of cross-reactive HuNoV vaccines.