The present invention provides an immune effector cell that comprises a chimeric antigen receptor (CAR) specific for a tag of a tagged polypeptide, wherein said polypeptide binds to an antigen of a target cell, and a chimeric costimulatory receptor (CCR) specific for a further antigen. The CCR is not able to mediate said immune response on its own but boosts the immune response of said immune effector cell triggered by the CAR.
