Mechanisms of Immune Evasion by The SARS-CoV-2 JN.1 Variant Against Broadly Neutralizing Antibodies

Objective With the continuous evolution of severe acute respiratory syndromes-coronary virus 2 (SARS-CoV-2) Omicron subvariants, particularly the emergence of BA.2.86 and its descendant JN.1, the efficacy of current neutralizing antibodies has faced substantial challenges. The JN.1 variant, noted for its pronounced immune evasion capacity, has rapidly become the globally dominant strain. Elucidating its escape mechanisms is therefore essential to guide the development of next-generation broad-spectrum vaccines and neutralizing antibody therapeutics. This study aimed to investigate the immune evasion mechanisms of JN.1 against broadly neutralizing antibodies, focusing on the effects of key receptor-binding domain (RBD) mutations on antibody binding and neutralization, thereby providing theoretical support for countering ongoing viral evolution. Methods We employed a multidisciplinary approach to systematically assess the binding and neutralizing activities of three broad-spectrum neutralizing antibodies (XGv074, XGv302, and XGv303) against BA.2.86 and JN.1. Binding affinities (KD values) of antibodies to variant RBDs were determined using bio-layer interferometry (BLI). Cryo-electron microscopy (cryo-EM) was used to resolve the structure of the BA.2.86 Spike trimer in complex with antibody antigen-binding fragments (Fabs), achieving a resolution of 3.47 Å for the BA.2.86 S-trimer bound to XGv302. Molecular dynamics simulations and binding free-energy decomposition were conducted to quantify the contributions of key mutations at the antibody-RBD interface. Additionally, sequence alignment and structural modeling were performed to evaluate the role of conformational flexibility in the antibody heavy-chain complementarity-determining region 3 (HCDR3) in mediating tolerance to mutations. Results Experimental data showed that XGv074, XGv302, and XGv303 retained neutralizing activity against BA.2.86 but exhibited markedly reduced binding to JN.1, with only XGv074 maintaining weak neutralization (IC50=2.3 mg/L). Cryo-EM structures revealed that all three antibodies targeted the RBD tip, overlapping with the ACE2-binding region. The JN.1-specific L455S mutation disrupted the hydrophobic interaction network between XGv302 and the RBD (involving key residues such as Y421 and L455), resulting in complete loss of neutralization. Binding free-energy decomposition further identified L455 and Y421 as energetic hotspots (ΔGConclusion The JN.1 variant escapes broad-spectrum neutralizing antibodies primarily through the L455S mutation in the RBD, which disrupts energetic hotspots and remodels the antibody-binding interface. Antibody conformational flexibility enhances adaptability to such mutations, providing new insights for broad-spectrum antibody design. These findings highlight the critical roles of epitope energy distribution and antibody flexibility in maintaining neutralization breadth, offering essential guidance for the rational design of next-generation vaccines and antibody therapeutics: specifically targeting conserved energetic hotspots while enhancing CDR flexibility to counter immune evasion driven by viral evolution.