Multipotent adult progenitor cells (MAPCs) are marrow-derived pluripotent stem cells with a broad differentiation potential. We sought to identify factors that affect adoptively transferred MAPCs. In vitro, MAPCs expressed low levels of major histocompatibility complex (MHC) antigens, failed to stimulate CD4 and CD8 T-cell alloresponses, and were targets of NK cytolysis. To study in vivo biodistribution, we labeled MAPCs with luciferase for sequential quantification of bioluminescence and DsRed2 for immunohistochemical analysis. C57BL/6 MAPCs were infused intravenously into C57BL/6, Rag-2/ (T- and B-celldeficient), and Rag-2//IL-2Rc/ (T-, B-, and NK-celldeficient) mice. In C57BL/6 mice, MAPCs were transiently detected only in the chest compared with long-term persistence in T- and B-cell deficient mice. NK depletion reduced MAPC elimination. Because the lungs were the major uptake site after intravenous injection, intra-arterial injections were tested and found to result in more widespread biodistribution. Widespread MAPC biodistribution and long-term persistence were seen in irradiated recipients given allogeneic marrow and MAPCs; such MAPCs expressed MHC class I antigens in tissues. Our data indicate that the biodistribution and persistence of reporter genelabeled MAPCs are maximized after intra-arterial delivery or host irradiation and that T cells, B cells, and NK cells contribute to in vivo MAPC rejection. (Blood. 2006;107:4182-4188) TSI通風(fēng)表/多參數(shù)通風(fēng)表