The present invention provides compositions and methods for regulating the specificity and activity of immune effector cells for use in immunotherapy. In one embodiment, the invention provides a type of chimeric antigen receptor (CAR) wherein the CAR is termed a “NKR-CAR” which is a CAR design comprising a component of a receptor naturally found on natural killer (NK) cells. In one embodiment, the NK receptor includes but is not limited to a naturally occurring activating and inhibitory receptor of NK cells known as a killer cell immunoglobulin-like receptor (KIR).