mAbs T-1A5 and ChT-1A5 bind to the FG-loop region of B7-H3 (homology modeling and peptide docking). (A) Schematic representation of B7-H3 structural domains generated using BioRender software. (B) Representation of different structural elements in the B7-H3 amino acid sequence shown in different colors. (C) 3D modeling and docked complexes of 2 predicted poses of the variable heavy (VH, upper panels) and variable light (VL, lower panels) chains of T-1A5 (surface representation) with the FG-loop in B7-H3 (green). Three complementary determining regions (CDRs) in VH and VL are shown in blue, red, and magenta. (D) Epitope mapping of B7-H3 peptides (5-amino-acid overlap, red) with T-1A5 or chimeric ChT-1A5 mAbs. B7-H3 full protein was used as a control. Peptide-5 and peptide-9 showed the strongest Kd values. (E) Raw traces of peptide-5 and peptide-9 of B7-H3 interacting with T-1A5 and ChT-1A5. (F) Model of peptide-5 (red) and peptide-9 (blue) in the extracellular domain of B7-H3.