BCMA-targeting Bispecific Antibody That Simultaneously Stimulates NKG2D-enhanced Efficacy Against Multiple Myeloma

B-cell maturation antigen (BCMA) is a highly plasma cell-selective protein expressed on malignant plasma cells of patients with multiple myeloma (MM), and it is a defined therapeutic target. Major histocompatibility complex class I-related chain A (MICA) is frequently expressed in lymphoproliferative malignancies including MM. MICA activates natural killer (NK) cells and costimulates T cells by interaction with its immunoreceptor NK cell receptor G2D (NKG2D). Nonetheless, during full-blown MM, tumor cells promote efficient MICA shedding, which evokes NKG2D internalization and immune suppression. To enhance the directional killing efficacy of immune cells against myeloma cells, we constructed a novel bispecific antibody 2A9-MICA and explored its potential antimyeloma activity against MM. 2A9-MICA consists of human MICA extracellular region and a single-chain antibody fragment (scFv) that targets BCMA generated by phage display technology. In vitro, 2A9-MICA activated NK cell-mediated cytotoxicity and induced NK cells to kill BCMA-positive human myeloma cells. Moreover, in BCMA-positive, MM-bearing nude mice, 2A9-MICA specifically targeted tumor tissue, where it effectively recruited immune cells and inhibited tumor tissue growth showed superior antitumor activity. Taken together, bispecific antibody 2A9-MICA provides a new approach for MM-targeting immunotherapy and has attractive potential for clinical applications.