Bispecific antibodies. (A) Bispecific T-cell engagers bring CD3⁺ T cells in proximity to cells expressing tumor antigen, to form an immunologic synapse and promote cell-mediated cytotoxicity. The Fc portion provides stability in the circulation, allowing for intermittent rather than continuous dosing, and can also promote antibody-dependent cellular cytotoxicity and complement activation. These constructs vary widely by agent, and the schematics shown are only representative. There can be variability in antigen-binding domains and dimerization (homodimers vs heterodimers), resulting in differences in antigen-binding sites (valency), geometry, size, and flexibility, all of which can result in different pharmacokinetic and pharmacodynamic properties. (B) Bispecific NK-cell engager, with 1 binding domain for the myeloma antigen and 1 for NK antigens leading to signal transduction and NK-cell activation.