Blinatumomab, which is comprised of two different single-chain variable fragment regions (scFv) linked via a glycine-serine linker (50), triggers a cytotoxic immune response and shows significant cytotoxic activity at ultra-low concentrations, through binding specifically to antigen CD19 that is overexpressed on the surface of B-cell ALL lymphocytes and antigen CD3 on the surface of T cells (51–53). This evidence concerns the gene CD19 and acute lymphoblastic leukemia.