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The following question is worthy of discussion. Submit comments to the cordbloodforum: medical.network@cordbloodforum.org
A transplant physician inquires:
How does one choose the optimal cord blood unit? A 4/ 6 or better HLA match seems important, but what degree of resolution of the HLA matching should be considered acceptable?
A director of an HLA laboratory at a major transplant center who is involved in selecting of the most appropriate stem cell products for transplantation at that center offers the following comment about selecting a cord blood unit:
"We usually use HLA-A,B, and DRB1 loci for consideration of matching. HLA-A and B are at low resolution (serological equivalent) and DRB1 is considered at high resolution (allele level). Usually we have not considered the DQB1 and HLA-C matching. We will look at the HLA-C if all else is matched. The major consideration in selection of a CB unit is cell dose, and then the match. We will not generally consider less than a 4/6 match."
A member of the Cord Blood Forum Editorial Board also replies:
There is no precise protocol for selection of the optimal cord blood unit for hematopoietic cell transplantation.
For most transplant centers, cell dose seems the first priority. A TNC of 1.5 x 107/kg has been a standard used frequently but more recently a dose of 2.0 or 2.5 x 107 TNC/kg or even higher has been requested by some transplant centers. Some transplant centers prefer to use CD34+ cells/kg or CFU results to select a unit, although such tests are not well standardized among cord blood banks so that the transplant centers that rely on CD34+ or CFU are using data obtained in their own laboratories. Many transplant centers do not have experience in performing these tests.
If a unit of acceptable cell dose is available, then the HLA match becomes the next consideration. Balancing cell dose with degree of HLA match in selecting among acceptable units seems to be more of an art form than a science. The article below provides one such example and points out that there is no definitive conclusion. After all, the first unrelated cord blood transplant was not done until 1993 which is only 11 years ago. Cord blood transplantation is still a young, evolving field.
The following article is pertinent and is reviewed in more detail on the Annotated Bibliography, IX. HLA, citation #10. A brief extract is provided below.
Factors associated with outcomes of unrelated cord blood transplant: guidelines for donor choice. Gluckman E, et al. Exp Hematol. 2004;32:397-407.
The authors conclude that their results show that two major factors, cell dose and HLA, can be used to choose a cord blood unit. A higher the number of cells and a lower the number of HLA disparities will increase the probability of engraftment; a higher the number of HLA disparities will increase the incidence of acute GVHD grade III-IV and decrease the risk of relapse.
There is difficulty in establishing, from the available data, consensual guidelines for donor choice based on HLA incompatibilities.
Would a cord blood unit with 4 x 107/kg nucleated cells (NCs) but no HLA disparities be preferable to a cord blood unit with 6 x 107 NCs but one HLA disparity? The authors state that no accurate answer to this point can be determined from their data.