Fig. 2: Broadly RBD-binding antibodies are persistent and primary vaccine-inducible.

a Immunization history for donor Q and R. Donor Q donated her blood ten months after her breakthrough infection of BA.2. Donor R received two doses of inactivated CoronaVac vaccines and experienced no breakthrough infection before blood donation. b Frequency of human B cells recognizing heterogenous bait proteins, PE-conjugated SARS-CoV-1 RBD and APC-conjugated XBB RBD, in donor Q and R. c Initial screening for mAbs (donor Q and R) with binding activity against both SARS-CoV-1 RBD and XBB RBD. Each pie chart represents a donor and the number indicates the isolated mAbs with naturally paired heavy and light chains from that donor. Four categorized mAbs based on ELISAs: red, binders against both SARS-CoV-1 RBD and XBB RBD; orange, antibodies binding only XBB RBD; green, antibodies binding only SARS-CoV-1 RBD; and white, mAbs with weak/no binding activity against both RBDs or mAbs with low expression level. d Broad ELISA binding activity. EC₅₀ values of representative mAbs (each line) isolated from donor Q and R were calculated based on ELISAs against 18 types of RBD proteins and 14 distinct S proteins. The gradient color represents the EC₅₀ values: red, <0.05 μg/ml; orange, 0.05-0.5 μg/ml; yellow, 0.5–5 μg/ml; light green, 5–10 μg/ml; and green, >10 μg/ml. Source data are provided as a Source Data file.