English: Development of neutralizing antibodies for treating COVID-19. In the receptor binding stage, the S1 subunit of SARS-CoV-2 binds human ACE2 on the host cell surface. Antibodies that bind the RBD domain on the S1 subunit might block the interaction of the RBD and the ACE2. In the viral fusion stage, after the cleavage of S1 subunit, the viral fusion peptide (FP) on the S2 subunit inserts into the host cell membrane, inducing the conformational change of the S2 subunit, which forms a six-helix bundle (6-HB) with the HR1 and HR2 trimers. Antibodies that target the HR domains might block viral fusion. Ab, antibody.