| Umbilical Cord Blood Transplantation: The Current Scientific Understanding Summary Objectives. To summarize the scientific literature on umbilical cord blood transplantation and present recommendations. Data Sources. Literature searches were conducted in the MEDLINE database for English-language articles published between 1989 to 2003 using the search term umbilical cord blood transplantation. The Lexis/Nexis news databases and the World Wide Web were searched using the "Google" search engine with the search term cord blood transplantation. Results. Challenges to the use of bone marrow-derived stem cells for hematopoietic stem cell transplantation include the time required to search for and evaluate a well-matched donor and peri-transplant toxicities, including graft-versus-host disease. Umbilical cord blood appears to be a viable alternative source for hematopoietic stem cells for transplantation. The primary factor limiting its success is the number of nucleated or CD34+ cells that are infused into the recipient during transplantation. Unlike bone marrow-derived stem cells, umbilical cord blood cells can engraft with up to 2 mismatches for the human leukocyte antigens. While time to engraftment appears to be delayed as compared to bone marrow transplants, for cord blood transplants using an acceptable cell dose (>3.0 x 107 cells/kg), the eventual rate of engraftment and patient survival are acceptable when compared to the rates reported with bone marrow transplants. Coupled with the short time frame needed to identify a suitable graft (14 days), umbilical cord blood transplantation may be especially useful for urgent transplants. The incidence of graft-versus-host disease in umbilical cord blood transplants also appears to be significantly lower and without a compromise to the graft-versus-leukemia effect, although more studies are needed to confirm this observation. Data on the speed and completeness of post-transplant immune recovery are limited for umbilical cord blood transplants. For young children, umbilical cord blood transplantation may be a very promising therapeutic option. Data in adults are more limited, but offer similar potential clinical benefits. The limitation of infused nucleated cell dose is currently the subject of intense research. Techniques have been identified to increase the efficiency of the yield of cells from the harvest procedure, and studies are beginning to explore the feasibility of mixing unrelated donor umbilical cord blood cells for infusion as a singe graft. Finally, research is being conducted into the ex vivo expansion of umbilical cord blood cells prior to transplantation with the goal of identifying techniques by which existing umbilical cord blood cells can be increased in number without a compromise to their engraftment and immune reconstitution functions. One clinical feasibility trial has been reported. Conclusions. The American Medical Association believes that the use of umbilical cord blood as an alternative source of hematopoietic stem cells for transplantation is appropriate. The decision to use bone marrow-derived cells or umbilical cord-derived cells should be considered for each individual case. Due to cord blood’s potential as a plentiful and safe source of stem cells, research into the methods that will improve the use of umbilical cord blood-derived hematopoietic stem cells for transplantation must continue. This includes research into the ex vivo expansion of umbilical cord blood-derived hematopoietic stem cells; the combination of multiple units of closely matched, unrelated umbilical cord blood cells for transplantation; and the improvement of umbilical cord blood cells collection techniques. RECOIMMENDATIONS The following statements, recommended by the Council on Scientific Affairs, were adopted by the AMA House of Delegates as AMA policy and directives at the 2003 AMA Annual Meeting:
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