Control Devices are disclosed including RNA destabilizing elements (RDE), RNA control devices, and destabilizing elements (DE) combined with Chimeric Antigen Receptors (CARs) or other transgenes in eukaryotic cells. Multicistronic vectors are also disclosed for use in engineering host eukaryotic cells with the CARs and transgenes under the control of the control devices. These control devices can be used to optimize expression of CARs in the eukaryotic cells so that, for example, effector function is optimized. CARs and transgene payloads can also be engineered into eukaryotic cells so that the transgene payload is expressed and delivered after stimulation of the CAR on the eukaryotic cell.