Evaluating the breadth of neutralizing antibody responses elicited by infectious bursal disease virus (IBDV) genogroup A1 strains using a novel chicken B-cell rescue system and neutralization assay

Eight infectious bursal disease virus (IBDV) genogroups have been identified based on the sequence of the capsid hypervariable region (HVR) (A1-8), yet many vaccines are based on A1 strains. Given reported vaccine failures, there is a need to evaluate the ability of vaccines to neutralize the different genogroups. To address this, we used a reverse genetics system and the chicken B-cell line DT40 to rescue a panel of chimeric IBDVs and perform neutralization assays. Chimeric viruses had the backbone of a lab-adapted strain (PBG98) and the HVRs from diverse field strains: classical F52-70 (A1), US-variant Del-E (A2), Chinese-variant SHG19 (A2), very-virulent UK661 (A3), M04/09 distinct (A4), Italian ITA-04 (A6), and Australian-variant Vic-01/94 (A8). Rescued viruses showed no substitutions at amino-acid positions 253, 284, or 330, previously associated with cell-culture adaptation. Sera from chickens inoculated with wt (F52-70) or vaccine (228E) A1 strains had the highest mean virus neutralization (VN) titers against the A1 virus (log2 15.41 and 12.66), and the lowest against A2 viruses (log2 7.41-7.91, p=0.0001-0.0274), consistent with A1 viruses being most antigenically distant from A2 strains, which correlated with the extent of differences in the predicted HVR structure. VN titers against the other genogroups ranged from log2 9.32-13.32, and A1 strains were likely more closely antigenically related to genogroups A3 and A4 than A6 and A8. Our data are consistent with field observations, validating our method, which can used to screen future vaccine candidates for breadth of neutralizing antibodies, and evaluate the antigenic relatedness of different genogroups. Importance There is a need to evaluate the ability of vaccines to neutralize diverse IBDV genogroups, and to better understand the relationship between HVR sequence, structure, and antigenicity. Here, we used a chicken B cell-line to rescue a panel of chimeric IBDVs with the HVR from seven diverse IBDV field strains, and conduct neutralization assays and protein modelling. We evaluated the ability of serum from vaccinated or infected birds to neutralize the different genogroups. Our novel chicken B-cell rescue system and neutralization assay can be used to screen IBDV vaccine candidates, platforms, and regimens for the breadth of neutralizing antibody responses elicited, evaluate the antigenic relatedness of diverse IBDV strains, and when coupled with structural modelling, elucidate immunodominant and conserved epitopes to strategically design novel IBDV vaccines in the future. ### Competing Interest Statement The authors have declared no competing interest.