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 V gamma 9 chain of the V gamma 9V delta 2(+) gamma delta T cell receptor and to AML target antigen, CD123, to selectively recruit V gamma 9(+) gamma delta T cells rather than pan T cells to target AML blasts. Our results suggest that prototypic bispecific antibodies (a) selectively activate V gamma 9(+) gamma delta T cells as judged by CD69 and CD25 surface expression, and intracellular Granzyme B expression, (b) selectively recruit V gamma 9(+) gamma delta T cells into cell-cell conjugate formation of gamma delta T cells with tumor cells indicating selective and effective engagement of effector and target tumor cells, and (c) mediate gamma delta T cell cytotoxicity (in vitro and in vivo) against tumor antigen-expressing cells. Collectively, these findings suggest that selectively redirecting V gamma 9(+) gamma delta T cells to target AML blasts has a potential for immunotherapy for AML patients and favors further exploration of this concept.