CD33 x Vδ2 TCR

Class

Bispecific T-cell engager (gamma-delta T-cell engager)

Pathway

Recruits and activates expanded Vδ2 T cells against CD33-expressing AML cells; low on-target/off-tumor toxicity to healthy hematopoietic cells

CD33 is a cell-surface protein found on immature and mature cells of the myeloid blood lineage, including the leukemic blasts that characterize acute myeloid leukemia (AML). Because CD33 is expressed broadly on AML cells, it has long been explored as a docking point for therapies designed to direct immune killing toward the tumor. This mechanism uses a bispecific molecule, an engineered antibody-like protein with two distinct binding arms, to physically link CD33-positive leukemia cells to a specific subset of the body's own cytotoxic lymphocytes: Vδ2 T cells, a population of gamma-delta T cells that recognize and destroy abnormal cells without depending on the conventional antigen-presentation machinery that alpha-beta T cells require. By binding CD33 with one arm and the Vδ2 T-cell receptor with the other, the molecule forces these T cells into close contact with leukemia cells, triggering direct cytotoxic activity. The choice of gamma-delta rather than the more commonly engaged alpha-beta T cells reflects an effort to achieve tumor killing while limiting the broad, systemic immune activation associated with some T-cell engaging therapies. This class of approach is relevant wherever leukemic cells display a shared surface marker with normal blood-forming tissue, since the central challenge is destroying the tumor without excessively damaging healthy blood cell production.