HuLuc63 triggers CS1-specific MM cell lysis through ADCC. (A) ADCC was performed by incubating calcein-AM–labeled target MM cells with human PBMC effector cells at an E/T ratio of 10:1, in the presence of various concentrations of HuLuc63 (■) or iso IgG1 (□). Percentage specific lysis was calculated, and data shown are representative of 3 experiments conducted with 3 different PBMC effector cell donors with similar results. HuLuc63 induces percent specific lysis of CS1-expressing MM lines in a dose-dependent manner. (B) Cytospin preparation of MM1S cells cultured with PBMC effector cells in the presence of HuLuc63 mAb (0.01 μg/mL) for 30 minutes was stained with Giemsa-Wright (Fisher Scientific, Springfield, NJ; original magnification ×200). (C) CS1 expression in 8 MM lines is determined by immunoblotting using anti-CS1 mAb. Only U266 has barely detectable CS1. (D) HuLuc63 does not stimulate dose-dependent ADCC against CS1− U266 MM line or CD19+ B cells from 2 healthy donors (open symbols), whereas it significantly induces lysis of CS1-expressing MM1R and MM1S target cells (solid symbols).
