A Three-Dimensional Scaffold-Based System for Modeling the Bone Marrow Tissue Yousof Gheisari, 1 Mohammad Vasei, 2,3 Abbas Shafiee, 4 Masoud Soleimani, 5 Ehsan Seyedjafari, 1,6 Azadeh Omidkhoda, 7 Ladan Langroudi, 1 and Naser Ahmadbeigi 3 Hematopoietic stem and progenitor cells (HPC) niche, consisting of HPC and their surrounding stromal com- ponents, is the fundamental unit for bone marrow (BM) tissue engineering. Previously, mouse BM-derived cell complexes with HPC niche unit properties called ‘‘niche-like units’’ were isolated and characterized. This study was aimed to evaluate the possibility of bioengineering marrow tissue in heterotypic sites using niche-like units in combination with three-dimensional scaffolds. BM niche-like units were isolated from GFP-transgenic C57BL/6 mice and seeded on electrospun poly (L-lactide) nanofiber scaffolds, which were then roll-folded and aseptically implanted into the peritoneal cavity of irradiated wild-type mice. One month after implantation, donor-derived cells were detected in peripheral blood of the recipients and contributed to restoration of all blood lineages. The transplanted bioengineered tissue histologically resembled native BM structure and was connected to the mouse systemic circulation. Long-term self-renewal was confirmed by serial transplantation into tertiary recipients. In conclusion, this study establishes a novel system for BM tissue engineering, which can be used to improve the HPC transplantation outcomes especially in cases where HPC niche is damaged and also as an in vivo model to test the effects of different factors on hematopoiesis. Introduction H ematopoietic stem and progenitor cells (HPC) transplantation has been widely used for the treatment of broad range of disorders since the first successful HPC transplantation in 1950s [1,2]. In traditional approach, both hematopoietic and nonhematopoietic cellular components of bone marrow (BM) are transplanted [3,4]. However, in vivo HPS reside in a complex microenvironment called HPC niche, which is essential for proper function of HPC [5,6]. In recent years a large number of studies have been performed to characterize the cell types and molecules that comprise the hematopoietic stem cell niche [7,8]. An essential indicator that HPC niche might in fact have essential impact on HPC transplantation comes from transplantation of HPC into pa- tients with damaged niche [9,10]. In some unhealthy situa- tions such as acute myeloid leukemia, myelodysplastic syndrome, and aplastic anemia, the interaction between HPC and their niche is damaged, so the success rate of transplan- tation is substantially low [11–13]. Furthermore, in most current BM transplantation approaches the HPC are isolated and then transplanted into the recipient as single cells and literally the impact of niche components is not considered and might impact the clinical outcomes. More recently, HPC cocultured with niche cellular components and some BM extracellular matrix (ECM) proteins as a simplified way to improve HPC transplantation outcomes [14–16]. Lately, some studies have been performed as a potential ex vivo model to uncover mechanisms that are involved in BM niches to describe the fundamental interactions of the niche com- ponents, and also as another way to enhance the HPC trans- plantation results, especially in disorders that BM stroma is damaged [17–21]. However, results were promising but modest, which may be due to the fact that all niche compo- nents were not taken into account. In previous studies we isolated and characterized unique cellular complexes from bone marrow called BM HPC niche-like units based on size fractionation [18,22]. In cul- ture experiments confirmed BM cellular complexes were the origin of both BM-mesenchymal stem cells (BM-MSCs) and 1 SABZ Biomedicals Research Center, Tehran, Iran. 2 Department of Pathology, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. 3 Liver and Pancreatobiliary Diseases Research Center, Digestive Disease Research Institute, Tehran University of Medical Sciences, Tehran, Iran. 4 The University of Queensland Centre for Clinical Research, Herston Campus, Brisbane, Australia. 5 Department of Hematology, Tarbiat Modares University, Tehran, Iran. 6 Department of Biotechnology, College of Science, University of Tehran, Tehran, Iran. 7 Department of Hematology and Blood Banking, School of Allied Medical Sciences, Tehran University of Medical Sciences, Tehran, Iran. STEM CELLS AND DEVELOPMENT Volume 25, Number 6, 2016 Ó Mary Ann Liebert, Inc. DOI: 10.1089/scd.2015.0182 492