Efficient elimination of chronic lymphocytic leukaemia B cells by autologous T cells with a bispecific anti-CD19/anti-CD3 single-chain antibody construct

Recently, we have shown that a novel recombinant bispecific single-chain antibody construct (bscCD19xCD3), induces highly efficacious lymphoma-directed cytotoxicity mediated by unstimulated peripheral T lymphocytes. Functional analysis of bscCD19xCD3 has so far been exclusively performed with human B lymphoma cell lines and T cells from healthy donors. Here we analysed the properties of bscCD19xCD3 using primary B cells and autologous T cells from healthy volunteers or patients with B-cell chronic lymphocytic leukaemia (B-CLL). We show that bscCD19xCD3 induces T-cell-mediated depletion of nonmalignant B cells in all four cases and depletion of primary lymphoma cells in 22 out of 25 cases. This effect could be observed at low effector-to-target (E:T) ratios and in the majority of cases without additional activation of autologous T cells by IL-2. Even in samples derived from patients heavily pretreated with different chemotherapy regimens, strong cytotoxic effects of bscCD19xCD3 could be observed. The addition of bscCD19xCD3 to patients' cells resulted in an upregulation of activation-specific cell surface antigens on autologous T cells and elevated levels of CD95 on lymphoma B cells. Although anti-CD95 antibody CH-11 failed to induce apoptosis in lymphoma cells, we provide evidence that B-CLL cell depletion by bscCDxCD3 is mediated at least in part by apoptosis via the caspase pathway.