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The USA guidelines for cord blood selection recommend a minimum 4/6 (HLA-A, -B antigen, -DRB1 allele/ARD) match as asuitable option for some patients. Some of the WMDA member organisations have implemented to run a routine HLA-A, -B antigen, -DRB1 allele/ARD cord search with up to two mismatches as a default. Therefore, WMDA is implementing this option as well in Search & Match Service.

A, B Antigen, DRB1 ARD level CBU searches are now available in the sandbox environment (https://sandbox-search.wmda.info/). 

It was built to function in the same way as was implemented in legacy Search & Match. This means that: 

  • Allele matching is used to calculate overall and locus-specific match probabilities. 
  • Match class (e.g. 5/6, 4/6) is based on Antigen level matching at the A* and B* locus whereas regular matching at antigen recognition domain (ARD) level is used for DRB1.  

An antigen match is done according to method SI3 of this paper

World Marrow Donor Association framework for the implementation of HLA matching programs in hematopoietic stem cell donor registries and cord blood banks | Bone Marrow Transplantation (nature.com)

Examples of antigen matches and mismatches can be found in this table: 


After confirming it works correctly we will make it available in the production environment (https://searchmatch.wmda.info/)

Please help us in testing this feature. Please contact us at support@wmda.info if you have any questions. 

Match probabilities

Match probabilities for A, B Antigen, DRB1 ARD level CBU searches are calculated in the same way as "regular" searches. This means that the indicated overall and locus-specific match probabilities are based on ARD match, also for HLA-A and HLA-B. 

HLA match grade categorisation

Whether a potential CBU is a 6/6, 5/6 or 4/6 considering the special rules for A, B Antigen, DRB1 ARD level CBU searches is determined by whether it is an antigen match at HLA-A and HLA-B and whether it is an ARD level match at DRB1. Allele mismatches are therefore not considered regarding the categorisation. 

Sorting

Sorting is performed in the regular way based on the match probabilities as explained below. 

  1. HLA match grade (e.g. first 6/6 then 5/6, 4/6) 
  2. ARD level match probability in 10% intervals (descending)
  3. Number of total nucleated cells (TNC, descending) or, if chosen, CD34 count, descending

Known behaviour

As mentioned, CBUs are assigned the right match class (6/6 vs 5/6 vs 4/6) in A, B Antigen, DRB1 ARD level CBU searches. We are aware of a small issue. In some cases we may not indicate that a locus has a mismatch where there is one. This is only the case in A, B Antigen, DRB1 ARD level CBU searches and not in regular searches. We are working on a fix for this. 

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