HTT and infection: Approximately 1×107 A745 cells expressing the tetracycline repressor protein fused to the Krüppel associated box from human Kox1 (A745TKR) were transduced with murine leukemia virus (MLV) encoding the tetracycline repressor element at a multiplicity of infection of 0.1 and selected with 5 nM Hd-CDT, a toxin concentration high enough to cause death in parental cells.