Fig. 1
Structure, binding sites, and purity of three nanobody-based CD38-specific bispecific antibody recruiters (BARs). (a) Schematic illustration of different antibody constructs targeting CD38. The top row shows three nanobody-based BARs (30 kDa), each consisting of two nanobodies fused via a glycine-serine linker. The N-terminal nanobody in each of the three BARs recognizes one of three distinct epitopes on CD38: E1, pink; E2, blue; E3, green. The C-terminal nanobody is specific for human immunoglobulin kappa light chain (LCκ, white). The bottom row shows serum IgGκ (grey, left) and the conventional CD38-specific monoclonal human IgG1κ antibody daratumumab (yellow, right). Immunoglobulin light chain variable domain (VL), constant domain (CL), crystallizable fragment (FC), and targeted epitopes (E1–E3) are indicated in italics. (b) Schematic illustration of the binding sites of the three CD38-specific BARs. E1-BAR recognizes an epitope that overlaps with the epitope bound by daratumumab (E1). Both E2-BAR and E3-BAR bind distinct, independent epitopes on CD38 (E2, E3). CD38-specific BARs recruit serum IgGκ (grey) to CD38-expressing myeloma cells. The C-terminal nanobody (white) recognizes human kappa light chain while the N-terminal nanobody (pink, blue, or green) recognizes one of three epitopes on CD38. The interaction between serum IgGκ and CD38-BARs is illustrated using E1-BAR as a representative example. (c) Coomassie staining of an SDS-PAGE under reducing conditions with HEK cell supernatants of control-BAR, CD38-specific BARs (10 µL/lane), and purified daratumumab (1 µg/lane). The original uncropped gel is presented in Supplementary Figure S1.
