The application relates to a composition comprising:a stably integrating delivery vectora modified mammalian thymidylate kinase (tmpk) wherein the modified mammalian tmpk increases phosphorylation of a prodrug relative to phosophorylation of the prodrug by wild-type human tmpk anda detection cassette fused to tmpk.The application also relates to use of these compositions in methods of treatment of diseases such as graft versus host disease and cancer.
