Fig. 1

FMC63 and HI19α had different binding epitopes on CD19. a Homology models of hCD19 ECD (left), FMC63 scFv (middle), and HI19α scFv (right). b Docking mode of FMC63 and hCD19 ECD. Green, hCD19 ECD epitopes; purple, FMC63 epitopes. c Docking mode of HI19α and hCD19 ECD. Green, hCD19 ECD epitopes; purple, HI19α epitopes. d Sequence of hCD19 ECD. Gray background, predicted binding amino acid residues on hCD19 ECD with scFvs. Upper panel, interaction with HI19α; lower panel, interaction with FMC63. Red color, shared antigen epitopes; yellow color, key epitopes; green color, both shared antigen epitopes and key epitopes. e Partial interaction modes showed the non-bond interaction between scFvs and hCD19 ECD. Upper panel, HI19α scFv and hCD19 ECD; lower panel, FMC63 scFv and hCD19 ECD. Green, hCD19 ECD epitopes; purple, scFvs epitopes. f Flow cytometry analysis of the proportion of CD19⁺ Nalm-6 cells stained with indicated concentrations of the antibody. Left panel, HI19α antibody; right panel, FMC63 antibody. g Representative flow cytometry analysis showing the proportion of CD19⁺ cells on Nalm-6 cells stained with 0.017 pM HI19α and 0.042 pM FMC63