Control Devices are disclosed including RNA destabilizing elements (RDE) combined with transgenes, including Chimeric Antigen Receptors (CARs) in eukaryotic cells. These RDEs can be used to optimize expression of transgenes, e.g., 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 at desired times from the eukaryotic cell. Such CAR T-cells with transgene payloads can be combined with the administration of other molecules, e.g., other therapeutics such as anticancer therapies.