TBI overcomes MAPC resistance. To determine whether MAPC can persist under conditions of allogeneic hematopoietic stem cell transplantation, B6 mice were lethally irradiated and given B10.BR bone marrow intravenously with MAPC DLs infused intravenously (A) or intra-arterially (B). At day 30 after intravenous (IV) infusion, BLI signals from donor MAPC DLs were detected over thorax (A). After intra-arterial (IA) administration, bioluminescence was detected over the chest, abdomen, head, and extremities (B). (C) To quantify the engraftment of donor MAPCs, luciferase activity in tissue homogenates was determined at day 30 after cell infusions. After intra-arterial delivery, we detected tissue luminescence significantly higher than samples of the same tissues after intravenous delivery in spleen (P = .04), kidney (P = .03), and brain (P = .04). Lung luminescence was above background but was significantly lower after intra-arterial delivery when compared with lung luminescence after intravenous delivery (P = .01).