Abstract
A recently developed bispecific antibody construct, directed against CD19 and CD3 (bscCD19xCD3), induces T-cell-mediated lysis of allogeneic and autologous B cells in a specific and highly efficient manner. Since knowledge of the molecular mechanisms underlying this lysis is limited, a study on bscCD19xCD3-activated T-cell-effector pathways was performed. BscCD19xCD3-induced lysis of target B-cell lines Nalm-6, Daudi, and Raji and of autologous primary B cells is caused by the perforin-dependent granule-exocytosis pathway but not by the death ligands FasL, TRAIL, or TNF-alpha. When activated by bscCD19xCD3 and Raji cells, T cells express FasL mRNA, but incubation of Raji cells with cell-free supernatants from cytotoxicity experiments caused an upregulation of c-Flipl, possibly accounting for the cells' insensitivity toward death-receptor-mediated lysis. In addition to granule exocytosis, Raji cells are lysed by at least one mechanism independent of perforin, which requires transport through the T cell's Golgi apparatus.