Internalization and cytotoxic assay. (A) The antigen-antibody complexes are endocytosed, and anti–IGSF9-DXd is fluorescently labeled with green, and anti–LAMP-1 is fluorescently labeled with red. (B-E) The different concentrations of anti–IGSF9-DXd are used to treat THP-1-IGSF9-WT, -KO, MV4-11, and U937 cells. (F-H) The cleaved PARP, pCHK1, and pH2A are detected by western blotting in THP-1 and MV4-11 cells. Ab, antibody; Con, concentration.