Many ABC transporter inhibitors stably enhance transduction in mPB CD34⁺ progenitors. (A) Cells were transduced with VRX494 in the presence of 50μg/mL verapamil (▪), 50 μM quinidine (♦), 100 μM diltiazem (▴), 1 mM probenecid (asterisk), 25 μM reserpine (□), and no drug (○ and dashed line). (B) Cells were transduced with VRX494 in the presence of 50 μg/mL verapamil (▪), 100 μM diltiazem (▴), 20 μM ritonavir (•), 250 μM sodium vanadate (⋄), and no drug (○ and dashed line).