Emergence of neutralizing RBD antibodies following Omicron infection with limited activity against ancestral SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evolution reduces the efficacy of prophylactic vaccines and monoclonal antibody (mAb) therapies. To evaluate potency and breadth, receptor binding domain (RBD)-targeting neutralizing mAbs were identified from patient B cells using an Omicron KP3.1.1 Spike (S) protein bait. MAbs exhibiting the greatest neutralization potency (1332D4 and 1332E5) and binding breadth (1324A10 and 1316C10) were evaluated in greater detail. Cryo-electron microscopy (Cryo-EM) studies revealed 1332D4 and 1332E5 target RBD residue segments 439-446 and 498-506 of KP3.1.1 S, respectively. 1332E5 is a knob498-506-targeting class-1/4 mAb that exhibits pan-Omicron specificity but does not bind or neutralize ancestral Wuhan-1. Further analysis suggests mAbs generically defined as class 1/4 mAbs may be separated into two classes. Class 1/4 mAbs, like 1332E5, and class 4/1 mAbs that make extensive interactions with the class-4 epitope and limited contacts with the class-1 knob498-596. Despite these differences, the specificity of both mAb classes can be altered by mutations in knob498-506.