E. Colletti, J. Wood, D.A. Ingram, E.D. Zanjani, M. Yoder, C. Porada, G. Almeida-Porada

Abnormal or inadequate vasculogenesis, local inflammation, and severe epithelial damage are common features of both inflammatory bowel disease (IBD) and radiation-induced injury resulting from pelvic or abdominal cancer treatment. Several studies have shown that adult bone marrow-derived stem cells, such as mesenchymal stem cells (MSC), upon transplantation, home to the damaged digestive tissue and facilitate mucosal repair in both IBD and radiation injury. Nevertheless, the levels of MSC intestinal engraftment are low, underscoring the need for finding ways to improve engraftment of these cells. It has also been shown that endothelial progenitor cells (EPC) exist in decreased numbers in the peripheral blood of IBD patients, which is in contrast to the presently held convention that the presence of an inflammatory state promotes the mobilization of EPC into the circulation. Furthermore, intestinal microvascular and endothelial cell dysfunction can lead to persistent tissue hypoperfusion and ischemia, further contributing to chronic inflammation. Therefore, here we investigated whether transplanted EPC can contribute to the intestinal vasculogenic process and/or the stem or mature epithelial cell pool of the intestine, and whether it is possible to identify and isolate a population of MSC exhibiting enhanced engraftment and/or contribution to the resident intestinal cellular pool. Using a fetal sheep model of in utero transplantation, we injected human cord blood-derived EPC or bone marrow-derived EphB2+ or EphB2- MSC and examined the ability of these cells to home to the intestine and contribute to the intestinal architecture. Recipients were evaluated at 85 days post-transplant for the presence of donor (human)-specific cell types by confocal microscopy. We found that within the intestine, EPC, as detected by DsRed positivity, localized preferentially to the mucosal layer above the muscularis mucosa in the area of the crypts of Lieberkühn. The overall levels of EPC engraftment positively correlated with the cell dose administered. Colocalization of DsRed cells with expression of Musashi, a putative marker for intestinal stem cells, was also evaluated. These analyses revealed that 10.79±0.01% of the epithelial cells within the crypts were DsRed positive and thus donor derived, and all expressed Musashi. Expression of this marker was not observed in any DsRed positive cells in any other location within the intestine. In addition, DsRed positive cells were found in the stromal layer adjacent to the crypts. We also showed that the EphB2high MSC subset had an enhanced ability to repopulate the ISC pool and to generate differentiated intestinal cells at higher levels than their EphB2low counterpart. We found that MSC localized preferentially to the mucosal layer and distributed equally between the crypts and the villi, with no evidence of cell fusion. Our studies demonstrate that both EPC and MSC can play a role in intestinal regeneration, and that a cell therapy platform using a combination of these cells may be ideally suited for repopulation of the intestinal stem cell pool and generation of differentiated intestinal cells.

Keywords (Optional): 
Endothelial Progenitor Cells
Mesenchymal Stem cells
Inflamatory Bowel Disease