Cross-neutralization and antigenic characterization of simian and equine group A rotaviruses

Rotaviral diarrhea in foals is caused by two dominant G3P[12] and G14P[12] genotypes of equine rotavirus A (ERVA). Protection of foals against ERVA infection and disease is achievable by passive antibody transfer through colostrum from mares receiving inactivated monovalent G3P[12] vaccine. Simian rotavirus SA11 G3P[2] is also included in ERVA vaccines to protect foals. Here, we characterized cross-neutralization and protection among three distinctive rotaviruses carrying the same or different G (defined by VP7) or P (defined by VP4) genotype by using a rabbit and equine monospecific antisera panel coupled with structural and computational analyses of viral epitopes. Data from these experiments demonstrated that (i) rSA11 G3P[2] and equine G3P[12] neutralized well with each other in rabbit antisera but with less cross-neutralization capacity against equine G14P[12]; (ii) interestingly, rabbit antisera to equine G14P[12] provided more robust cross-protection against rSA11 G3P[2] than the reverse; (iii) despite only a few amino acid differences in VP8* between two equine viruses, rabbit antisera to VP8* of equine G3P[12] moderately cross-neutralized G14P[12] but with potent neutralizing activity against rSA11 G3P[2]; (iv) surprisingly, the breadth and magnitude of cross-neutralization among three viruses in equine antisera were broader and stronger than those observed in rabbit antisera; and (v) multiple highly solvent-exposed amino acid residues conserved in VP7 and VP8* among three viruses may serve as novel B cell epitopes that contribute to the observed cross-neutralization. Taken together, these results highlight that cross-neutralization determinants among different rotaviruses are complex and dependent on specific viral context and animal species.

Our findings support that the G genotype determined by the VP7 protein plays a more important role, within the virus panel examined in this study, in determining broad neutralization specificity than previously thought. Our work has implications for vaccine design, suggesting that the inclusion of diverse G genotypes may be necessary to achieve broader protection. The P genotype, determined by the VP4 protein, exhibited variable levels of cross-neutralization, indicating that the P genotype alone may not be sufficient to induce strong cross-neutralization among different rotaviral strains. G genotype- or VP7-driven cross-protection may be conferred by novel epitopes identified structurally in this study. Finally, our study revealed that horse sera were more capable of cross-neutralizing different equine and simian rotaviruses than rabbit sera. This finding has implications for vaccine development, underscoring the need to evaluate candidate vaccines across multiple species or in species-relevant models to ensure broad and effective vaccine-mediated protection against rotavirus infection.