Spike s1 protein

Human antibody transgenic mice were generated by Boan Biotechnology. Mice were bred and kept under specific-pathogen-free conditions.
Three mice (named Q1–Q3) were immunized in 10-day intervals with the mixture of recombinant RBD protein (Cat 40592-V05H, Sino Biological), Spike S1 protein (Cat 40591-V02H, Sino Biological) and Spike S2 protein (Cat 40590-V08B, Sino Biological) and boosted by 105 μg mixtures (35 μg for each protein) after three rounds immunization. Two mice (named Q6 and Q7) were immunized in 10-day intervals with recombinant Spike S1 + S2 (Cat 40589-V08B1, Sino Biological) and boosted by 40 μg recombinant Spike S1 + S2 after 3 rounds of immunization. Another two mice (named Q14, Q15) were immunized in 10-day intervals with mixtures of Spike S1 protein (Cat 40591-V02H, Sino Biological) and RBD protein (Cat 40592-V05H, Sino Biological) and boosted by 70 μg mixtures (35 μg for each protein) after three rounds immunization. Genes of these proteins were derived from the SARS-CoV-2 strain (Wuhan-1 strain, GenBank: MN_908947). The antibody titers were tested by Elisa. After three rounds of immunization and one boost, spleen cells were harvested after 3 days of the last boost for phage libraries construction. Supplementary Table 1 showed details for the immunization process and Supplementary Fig. 2 showed serum antibody titers after three rounds of immunization.