Horwitz et al."8 used allogeneic unmanipulated HLA identical or singleantigen mismatched sibling bone marrow transplants in three patients with osteogenesis imperfecta to markedly reduce their fracture rate and skeletal growth. Proof that new osteoblasts were derived from grafted bone marrow was made by identification of Y chromosome in female recipient patient 1 and DNA polymerism in patient 2. This is surprising as the stem cells do have HLA type 2 antigens, but these are the least antigenic type.
Cultured allogeneic embryonal chondrocytes were implanted into defects in an avian model and the results were good.99-100 As human embryonal tissue is difficult to obtain and ethical problems are raised, MSCs from bone marrow represent an alternative source of pluripotential stem cells. These cells have been cultured in vitro and induced to form cartilage prior to implantation into the chondral defects in rabbits.89101 Goat articular cartilage has also been resurfaced by chondrocytes derived from bone marrow.102 In this study, bone marrow was aspirated from the iliac crest of 12 adult white goats, and chondrogenesis of the MSCs was induced. Four goats were transplanted with allogeneic implants, four with autogeneic implants; as all the implants had been impregnated in a hyaluronic acid preparation, the four goats which served as controls had their defects treated with hyaluronic acid only. Macroscopic evaluation indicated that the defects treated with autogeneic implants all filled with a hyaline-like tissue, while the defects from the allogeneic group were only partially filled, and the control groups were not filled at all. This would suggest that allogeneic MSCs can induce tissue regeneration but not as successfully as autologous MSCs.
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