Oligomerized receptor binding domain blocks pan-sarbecovirus infection via enhanced avidity to host receptor.

Continuous mutation of viruses enables evasion of established immune defenses and therapeutics. Here we report a broad-spectrum therapeutic design, termed HRBD, that mimics viral invasion-associated molecular patterns. HRBD demonstrated potent and broad-spectrum inhibition against Pangolin-CoV, SARS-CoV, SARS-CoV-2, and its variants, lowering the half-maximal inhibitory concentration (IC50) by approximately 1000-fold compared to the monomeric RBD. Furthermore, HRBD effectively suppressed syncytium formation induced by the spike proteins of sarbecoviruses, an effect not observed with the monomeric RBD. In hACE2-transgenic mice challenged with SARS-CoV-2, intranasal administration of HRBD reduced viral loads in lung and tracheal tissues by ∼106-fold, with no detectable immunogenicity. Binding analyses revealed that HRBD achieved approximately 1000-fold stronger avidity for hACE2 compared to the RBD monomer, superior to the high-affinity RBD-62 mutant generated by directed evolution, without affecting hACE2 enzymatic activity or subcellular localization. Oligomerization characterization confirmed that HRBD predominantly formed heptamers, visualized as ∼10 nm diameter rings via transmission electron microscopy. This mimicking strategy offers a viable approach for developing broad-spectrum therapeutics against current and future antigenically variable viruses.