460. Transplantation of Human Aldehyde Dehydrogenase Expressing Cells Leads to Widespread Tissue Distribution of Donor Cells in the Pancreas and Liver of NOD/SCID/MPSVII Mice
Authors: David A. Hess, Timothy P. Craft, Louisa Wirthlin, Phillip E. Herrbrich, Alex A. Hofling, Mark S. Sands, Jan A. Nolta
Journal: Molecular Therapy (2005)

Beta-glucuronidase (GUSB) is a lysosomal enzyme expressed in virtually all cell types. Transplantation of GUSB-expressing human hematopoietic stem cells (HSC) into the GUSB-deficient NOD/SCID/MPSVII mouse allows for the detection of xenotransplanted cells in hematopoietic and non-hematopoietic tissues, without reliance on the expression of human-specific cell surface markers or in situ hybridization (Hoffing, 2003). We are currently using the NOD/SCID/MPSVII model to investigate the transfer of the GUSB gene from human cells into murine cells of GUSB deficient tissues. We recently characterized a novel population of reconstituting HSC from human umbilical cord blood (UCB) by lineage depletion (Lin-) and selection of cells with high aldehyde dehydrogenase (ALDH) activity (Hess, 2004). These ALDHhiLin- cells demonstrate robust hematopoietic engraftment in the NOD/SCID model and contain a subpopulation of cells (ALDHhiCD133+) that may not be fully restricted to hematopoietic lineages. Here, we have used the NOD/SCID/MPSVII model to study the tissue distribution of ALDHhiLin- cells in multiple organs. Tail vein injection of 2|[times]|105 ALDHhiLin- cells into sub-lethally irradiated (300cGy) NOD/SCID/MPSVII mice (n=6) demonstrated hematopoietic chimerism in the BM (70.5|[plusmn]|15.1%), spleen (7.0|[plusmn]|2.8%) and peripheral blood (17.0|[plusmn]|10.7%). In contrast, injection of 106 ALDHloLin- cells (n=5) did not produce consistent human cell engraftment. By using GUSB-specific histochemical staining, significant human engraftment was also detected in the non-hematopoietic (liver, pancreas, kidney, lung, heart, and brain) tissues of mice transplanted with ALDHhiLin- cells. GUSB activity was co-localized with CD45 expression in the BM of mice transplanted with ALDHhiLin- cells. However, flow cytometric analysis of liver tissue revealed a discrepancy between engraftment detected by a fluorescent GUSB substrate, compared to human CD45 cell surface expression. Histochemical staining confirmed the presence of GUSB+ cells that did not express human CD45, and uncovered GUSB expressing cells with typical hepatocyte morphology. These hepatocyte-like GUSB+ cells were also present after the transplantation of the ALDHhiCD133+Lin- subpopulation (n=4). In the pancreas, GUSB+ donor cells were localized in ductal regions and surrounding recipient islets. The ALDHhiLin- UCB cells demonstrated a previously uncharacterized high level of engraftment in non-hematopoietic organs of NOD/SCID MPSVII mice. We are currently investigating cellular fusion and nuclear reprogramming as a putative mechanism for the production of non-hematopoietic cells expressing donor cell-derived GUSB. This gene transfer potentially occurs through spontaneous fusion as previously demonstrated in liver (Willenbring, 2004) and muscle (Camargo, 2004). This phenomenon may be further exploited to deliver target genes into various tissues for the treatment of genetic abnormalities.