Cellular immunotherapy has attracted increasing interest in genetic modification of immunologically competent cells in order to activate the effector cell after binding to predefined antigen. The chimeric immune-receptor strategy utilizes recombinant receptor molecules that are grafted on the surface of effector cells and comprise an extracellular antigen-binding domain and an intracellular signaling domain. The antigen-binding domain is a scFv (single-chain fragment of variable regions) derived from an antibody and is fused to a transmembrane moiety and an intracellular signaling domain that mediates cellular activation upon receptor crosslinking by binding of the scFv domain to antigen. This design of a chimeric receptor molecule combines the specific binding to predefined ligands with the initiation of intracellular signaling pathways for cellular activation (1 ).