The invention provides improved compositions for adoptive cell therapies for cancers. The invention generally provides improved vectors for generating T cell therapies and methods of using the same. More particularly, the invention provides salvage CARs, dimerizable salvage receptors, and their use in treating, preventing, or ameliorating cancers, and in particular preferred embodiments relapsed or refractory cancer. In various embodiments, a salvage chimeric antigen receptor (CAR) is provided comprising: an extracellular antigen binding domain; a multimerization domain; a transmembrane domain; one or more intracellular co-stimulatory signaling domains; and/or a primary signaling domain.