An IgG-like fusion protein comprising an anti-Spike S2 antibody and ACE2 exhibits potent and broad neutralization against SARS-CoV-2 and variants of concern

Background The continuous evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) highlights the value of broad-spectrum antiviral strategies. Antibody-engineering approaches targeting conserved regions of the Spike protein may enhance neutralizing potency and breadth. Methods A human antibody (P23) against the Spike protein of SARS-CoV-2 was identified using a human antibody phage display library panning and screening for binding affinity and breadth against multiple coronavirus Spike proteins using surface plasmon resonance (SPR). The epitope of P23 was characterized using the S1 and S2 subunits of SARS-CoV-2 Spike protein and hydrogen–deuterium exchange mass spectrometry (HDX-MS). An IgG–like bispecific fusion protein (Bs-ACE2-P23) was engineered by fusing the extracellular domain (ECD) of human angiotensin-converting enzyme 2 (ACE2) to the N-terminus of the P23 heavy chain (HC). Neutralizing activity was evaluated against both pseudotyped and authentic SARS-CoV-2 variants. Results P23 cross-bound Spike proteins from SARS-CoV-2 wild type (WT), D614G and JN.1 variants, Pangolin-CoV, Bat coronavirus RaTG13, and SARS-CoV-1, recognizing an epitope on the S2 subunit adjacent to the fusion peptide (FP). While P23 was ineffective against D614G-containing SARS-CoV-2 variants, Bs-ACE2-P23 exhibited markedly enhanced neutralization potency. This bispecific architecture also improved the neutralizing activity of another FP-targeting antibody. Conclusions We developed a bispecific fusion protein with potent broad-spectrum neutralizing activity against SARS-CoV-2 variants. This architecture provides a promising strategy for next-generation coronavirus biologics.