Selective recruitment of γδ T cells by a bispecific antibody for the treatment of acute myeloid leukemia

Despite significant progress over the last few decades in the treatment of acute myeloid leukemia (AML), there still remains a major unmet medical need for this disease. Immunotherapy approaches for redirecting pan CD3(+) T cells to target leukemia blasts have shown limited efficacy in clinical trials and often accompanied with severe toxicity in AML patients. We designed an alternative engager molecule (Anti-TRGV9/anti-CD123), a bispecific antibody that can simultaneously bind to the Vγ9 chain of the Vγ9Vδ2(+) γδ T cell receptor and to AML target antigen, CD123, to selectively recruit Vγ9(+) γδ T cells rather than pan T cells to target AML blasts. Our results suggest that prototypic bispecific antibodies (a) selectively activate Vγ9(+) γδ T cells as judged by CD69 and CD25 surface expression, and intracellular Granzyme B expression, (b) selectively recruit Vγ9(+) γδ T cells into cell–cell conjugate formation of γδ T cells with tumor cells indicating selective and effective engagement of effector and target tumor cells, and (c) mediate γδ T cell cytotoxicity (in vitro and in vivo) against tumor antigen-expressing cells. Collectively, these findings suggest that selectively redirecting Vγ9(+) γδ T cells to target AML blasts has a potential for immunotherapy for AML patients and favors further exploration of this concept.