Since the first cord blood transplant successfully performed in a child with Fanconi anemia with his HLA-identical sibling, the number of allogeneic unrelated and related transplants performed for various hematological disorders is increasing steadily. To perform these transplants, cord blood banks are dedicated for collecting, cryopreserving, and performing searches for international exchanges.
More than 8000 unrelated cord blood transplants have been performed worldwide; the transplants have been provided by cord blood banks that have collected more than 200,000 cord blood units. Cord blood cells have proliferative advantage and decreased immune reactivity when they are compared to adult bone marrow cells. These properties give a clear advantage for engraftment and diminution of graftversus-host disease. In consequence, several studies have shown that cell dose and HLA are important factors for survival after transplant. The best units should contain more than 2 × 107 nucleated cells per kilogram and more than 2 × 105 CD34+ cells per kilogram, the number of HLA mismatches should not be superior to 2. The advantages of cord blood compared to bone marrow transplants are the absence of risk to the donor, the direct availability of the cells, and the absence of infectious disease at birth. Further research are currently undertaken to improve the results of allogeneic hematopoietic stem cell transplants: they include the use of double cord blood transplants, the preparative regimen with non-myeloablative drugs, and the in vitro expansion of progenitor cells.
In addition to the presence of hematopoietic progenitors, it is now known when cord blood contains stem cells that have retained embryonic properties, they can be isolated, and, when cultured in appropriate conditions, give rise to cell lines that can be used for tissue engineering and regeneration of non-hematopoietic organs or tissues. Already, various cell lines have been generated from cord blood, including mesenchymal cells, endothelial cells, hepatocytes, muscle, cardiac myoblasts, pancreatic islets, keratinocytes, and neuronal cells. These results are very promising, but more research is needed before large-scale production for clinical use. Comparison with adult and embryonic stem cells will determine the best source for each indication. Considering the availability of cord blood and the absence of ethical problems, cord blood will probably become the best source for cell therapy.
