The continuous emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with increased transmissibility and profound immune-escape capacity makes it an urgent need to develop broad-spectrum therapeutics.Nanobodies have recently attracted extensive attentions red label violin strings color code due to their excellent biochemical and binding properties.Here, we report two high-affinity nanobodies (Nb-015 and Nb-021) that target non-overlapping epitopes in SARS-CoV-2 S-RBD.Both nanobodies could efficiently neutralize diverse viruses of SARS-CoV-2.
The neutralizing mechanisms for the two nanobodies are further delineated by high-resolution nanobody/S-RBD complex structures.In addition, an Fc-based tetravalent nanobody format is constructed by combining Nb-015 and Nb-021.The resultant nanobody conjugate, designated as Nb-X2-Fc, exhibits significantly enhanced breadth and potency against all-tested SARS-CoV-2 variants, including Omicron sub-lineages.These data demonstrate that d2 fleshripper Nb-X2-Fc could serve as an effective drug candidate for the treatment of SARS-CoV-2 infection, deserving further in-vivo evaluations in the future.