Abstract: Embodiments of the disclosure include methods and compositions that allow for development of efficient chimeric antigen receptors (CARs) by selecting appropriate spacer content and/or length by balancing the effects of tonic signaling with the efficacy of antigen recognition for the spacer. In specific embodiments, the CH3 domain from IgG2 is utilized as a spacer. In specific embodiments, T cell metabolic activity is utilized as a measure of tonic signaling to facilitate determination of suitable CAR constructs. In other embodiments, cells bearing chimeric Fc receptor target molecules are utilized to target Fc gamma receptor (FcR)-bearing for the purpose of their destruction.