Mechanistic Insights and Advances of Bispecific T Cell Engaging Antibodies Therapy in Multiple Myeloma.

Multiple myeloma (MM) is a clonal malignancy of terminally differentiated plasma cells characterized by bone marrow infiltration and excessive production of monoclonal immunoglobulins, leading to end-organ damage such as osteolytic bone lesions. Despite substantial therapeutic progress achieved with proteasome inhibitors, immunomodulatory drugs, and anti-CD38 monoclonal antibodies, multiple myeloma remains incurable, and outcomes for triple-class-refractory patients remain dismal, with median survival below one year. Bispecific T cell engaging antibodies (TCEs) have recently emerged as a promising immunotherapeutic approach capable of redirecting cytotoxic T cells to eliminate malignant plasma cells. 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. This review summarizes the molecular design, mechanism of action, and clinical development of TCEs in MM, encompassing early bi-specific T cell engagers (BiTE) constructs such as AMG 420 and next-generation IgG-like molecules including teclistamab. Pivotal clinical trials have demonstrated overall response rates between 43% and 73%, accompanied by durable remissions and manageable safety profiles. Future directions include earlier-line integration, synergistic combinations with immunomodulatory or costimulatory agents, and the development of trispecific formats to overcome antigen escape and T cell exhaustion. Collectively, TCEs represent a paradigm shift toward durable, immune-mediated disease control in multiple myeloma.