TNFRSF17 and neoplasm: By culturing BM mononuclear cells (BMMC) isolated from patients, we were able to (1) test TNB‐383B's ability to promote PC lysis and CTL degranulation, (2) assess cytokine responses induced by TNB‐383B, (3) determine the mechanism of TNB‐383B‐induced cell death ex vivo, and (4) identify tumor variables (BCMA expression) and tumor microenvironment variables (E:T ratio) potentiating TNB‐383B activity.