PRF1 and neoplasm: These engineered antibodies simultaneously engage CD3 on T cells and a tumor-associated antigen such as B cell maturation antigen (BCMA), G protein-coupled receptor family C group 5 member D (GPRC5D), or Fc receptor homolog 5 (FcRH5), thereby forming an immune synapse that triggers T cell activation, cytokine secretion, and perforin–granzyme-mediated apoptosis of the targeted B cell.