RESUMEN
The ongoing mutations of the SARS-CoV-2 pose serious challenges to the efficacy of the available antiviral drugs, and new drugs with fantastic efficacy are always deserved investigation. Here, a nanobody called IBT-CoV144 is reported, which exhibits broad neutralizing activity against SARS-CoV-2 by inducing the conformation of spike trimer dimers. IBT-CoV144 was isolated from an immunized alpaca using the RBD of wild-type SARS-CoV-2, and it showed strong cross-reactive binding and neutralizing potency against diverse SARS-CoV-2 variants, including Omicron subvariants. Moreover, the prophylactically and therapeutically intranasal administration of IBT-CoV144 confers fantastic protective efficacy against the challenge of Omicron BA.1 variant in BALB/c mice model. The structure analysis of the complex between spike (S) protein, conducted using Cryo-EM, revealed a special conformation known as the trimer dimers. This conformation is formed by two trimers, with six RBDs in the "up" state and bound by six VHHs. IBT-CoV144 binds to the lateral region of the RBD on the S protein, facilitating the aggregation of S proteins. This aggregation results in steric hindrance, which disrupts the recognition of the virus by ACE2 on host cells. The discovery of IBT-CoV144 will provide valuable insights for the development of advanced therapeutics and the design of next-generation vaccines.
RESUMEN
Highly pathogenic H5N1 virus infection causes severe disease and a high rate of fatality in humans. Development of humanized monoclonal antibodies may provide an efficient therapeutic regime for H5N1 virus infection. In the present study, broadly cross-reactive monoclonal antibodies (MAbs) derived from mice were humanized to minimize immunogenicity. One chimeric antibody (cAb) and seven humanized antibodies (hAbs) were constructed. These antibodies retained broad-spectrum reactivity to H5N1 viruses, binding to recombinant H5-subtype HA1 molecules expressed in CHO cells in a dose-dependent manner and exhibiting similar reactivities against antigenically distinct H5N1 viruses in hemagglutination inhibition (HI) assays. One humanized antibody, 37 hAb, showed HI and neutralization activities comparable to that of the parental murine antibody, 13D4 MAb, while the other six antibodies were less reactive to H5N1 viruses. Analysis of amino acid sequences in the variable region frameworks of the seven humanized antibodies found that Q5 and Y27 in the VH region are highly conserved murine residues. Comparison of the three-dimensional structures derived from the variable regions of MAbs 37 hAb, H1202-34, and 13D4 revealed that residue substitutions at sites 70 and 46 may be the major cause for the observed differences in binding affinity. Examination of the chimeric antibody and one of the humanized antibodies, 37 hAb, showed that both antibodies offered postinfection protection against lethal challenge with antigenically diverse H5N1 viruses in the mouse model. Chimeric and humanized antibodies which retain the broadly reactive and protective properties of murine H5-specific monoclonal antibodies have great potential for use in the treatment of human H5N1 infection.