The invention relates to the regulated expression of a chimeric antigen receptor (CAR) within a lentiviral vector. The CAR comprises a hook-binding domain that interacts with a hook, preferably encoded by the same lentiviral vector, which prevents proper processing and release of the CAR to the cell membrane. The invention encompasses vectors, methods of making the vectors, and methods of using them, including medicinal uses. The vectors can be used for administration to humans to induce immune responses and to treat cancers and tumors.