The present disclosure provides methods for genetically modifying lymphocytes and methods for performing adoptive cellular therapy that include transducing T cells and/or NK cells without prior ex vivo stimulation. The methods typically include engineered signaling polypeptides that can include a lymphoproliferative element, and/or a chimeric antigen receptor (CAR), for example a microenvironment restricted CAR. Additional elements of such engineered signaling polypeptides are provided herein, as well as vectors, such as retroviral vectors, packaging cell lines and methods of making the same. Furthermore, recombinant retroviruses and methods of making the same are provided. Numerous controls are provided, including riboswitches that are controlled, for example in vivo, by nucleoside analogues.