TNFRSF17 and neoplasm: Under these solid or heterogenous tumor conditions, ADCs with membrane-permeable payloads have advantages in gaining access to adjacent negative tumor cells via the “bystander effect.” To demonstrate the bystander activity of STI-8811, we cocultured BCMA-positive NCI-H929 and BCMA-negative K562 cell lines, treated with STI-8811 for 72 hours, and measured cytotoxicity in each cell line by flow cytometry.