Mapping the conformational epitope of a therapeutic monoclonal antibody against HBsAg by in vivo selection of HBV escape variants

Background and Aims Hepatitis B immunoglobulin (HBIG) has been routinely applied in the liver transplantation setting to block HBV reinfection of grafts. However, new monoclonal anti‐HBV surface antibodies have been developed to replace HBIG. The epitopes of such monoclonal antibodies may affect the emergence of escape variants and deserve study. Approach and Results The conformational epitope of sLenvervimab, a surrogate form of Lenvervimab, which is a monoclonal anti‐HBsAg antibody currently under phase 3 trial, was investigated by selecting escape mutants from a human liver chimeric mouse. HBV‐infected chimeric mice treated with sLenvervimab monotherapy showed an initial decline in circulating HBsAg levels, followed by a quick rebound in 1 month. Sequencing of circulating or liver HBV DNA revealed emerging variants, with replacement of amino acid E164 or T140, two residues widely separated in HBsAg. E164 HBV variants strongly resisted sLenvervimab neutralization in cell culture infection, and the T140 variant moderately resisted sLenvervimab neutralization. Natural HBV variants with amino‐acid replacements adjacent to E164 were constructed and examined for sLenvervimab neutralization effects. Variants with K160 replacement also resisted neutralization. These data revealed the conformational epitope of sLenvervimab. Conclusions Selection of antibody‐escape HBV variants in human chimeric mice works efficiently. Analysis of such emerging variants helps to identify anchor amino‐acid residues of the conformational epitope that are difficult to discover by conventional approaches.