A Bispecific Single-Domain Antibody Boosts Autologous V Gamma 9v Delta 2-T Cell Responses Toward Cd1d In Chronic Lymphocytic Leukemia

Purpose: Although considerable progress has been made with autologous T cell-based therapy in B-cell malignancies, application in chronic lymphocytic leukemia (CLL) lags behind due to disappointing response rates as well as substantial toxicity that is of particular concern in the elderly CLL population. V gamma 9V delta 2-T cells form a conserved T-cell subset with strong intrinsic immunotherapeutic potential, largely because of their capacity to be triggered by phosphoantigens that can be overproduced by CLL and other malignant cells. Specific activation of V gamma 9V delta 2-T cells by a bispecific antibody may improve the efficacy and toxicity of autologous T-cell-based therapy in CLL.Experimental Design: We evaluated CD1d expression in a cohort of 78 untreated patients with CLL and generated and functionally characterized a CD1d-specific V gamma 9V delta 2-T cell engager based on single-domain antibodies (VHH).Results: CD1d was expressed by CLL in the majority of patients, particularly in patients with advanced disease. The CD1d-specific V gamma 9V delta 2-T cell engager induced robust activation and degranulation of V gamma 9V delta 2- T cells, enabling V gamma 9V delta 2-T cells from patients with CLL to lyse autologous leukemic cells at low effector-to-target ratios. Expression of CD1d on CLL cells is upregulated by all-trans retinoic acid, and sensitizes the malignant cells to bispecific VHH-induced lysis. Furthermore, we provide evidence that the V gamma 9V delta 2-T cell receptor retains responsiveness to phosphoantigens when the bispecific VHH is bound, and aminobisphosphonates can therefore enhance bispecific V gamma 9V delta 2-T cell engager-mediated tumor-specific killing.Conclusions: Collectively, our data demonstrate the immunotherapeutic potential of this novel CD1d-specific V gamma 9V delta 2-T cell engager in CLL.