The Hutmacher laboratory recently demonstrated that it is possible to engineer a humanized HSC microenvironment in vivo. The group developed a highly reproducible method to engineer a humanized bone organ, which is able to recapitulate the morphological features and biological functions of the HSC niches. Transplantation of biodegradable tubular composite scaffolds seeded with differentiated human mesenchymal progenitor cells and loaded with rhBMP-7 resulted in the development of a chimeric bone organ including a large number of human mesenchymal cells that were shown to be metabolically active and capable of establishing a humanized microenvironment supportive for the lodgement and maintenance of functionally and physiologically defined host-derived HSCs. To our knowledge, we are the first group that could clearly show that human mesenchymal cells are not only incorporated in the newly formed bone organ but are indeed metabolically active and significantly contribute to the development of the HSC microenvironment. Finally, with this approach we are able to engineer a “blood producing” humanized organ bone.