Selective lysis of acute myeloid leukemia cells by CD34/CD3 bispecific antibody through the activation of γδ T-cells

Despite the considerable progress in acute myeloid leukemia (AML) treatment, relapse after allogeneic hematopoietic stem cell transplantation (HSCT) is still frequent and associated with a poor prognosis. Relapse has been shown to be correlated with an incomplete eradication of CD34+ leukemic stem cells prior to HSCT. Previously, we have shown that a novel CD34-directed, bispecific T-cell engager (BTE) can efficiently redirect the T-cell effector function toward cancer cells, thus eliminating leukemic cells in vitro and in vivo. However, its impact on gamma delta T-cells is still unclear. In this study, we tested the efficacy of the CD34-specific BTE using in vitro expanded gamma delta T-cells as effectors. We showed that the BTEs bind to gamma delta T-cells and CD34+ leukemic cell lines and induce target cell killing in a dose-dependent manner. Additionally, gamma delta T-cell mediated killing was found to be superior to alpha beta T-cell mediated cytotoxicity. Furthermore, we observed that only in the presence of BTE the gamma delta T-cells induced primary AML blast killing in vitro. Importantly, our results show that gamma delta T-cells did not target the healthy CD34intermediate endothelial blood-brain barrier cell line (hCMEC/D3) nor lysed CD34+ HSCs from healthy bone marrow samples.