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The match list presents all possible options. In order to help search coordinators to select the best potential stem cell source, WMDA will be implementing additional features to assist search coordinators, you can read the details of these features, below.
How to perform a three and/or four mismatch search for cord blood?
Three and four mismatch searches have been implemented for cord blood searches in Search & Match Service. This is a resource intensive service , therefore you first need to perform a two mismatch cord blood search before you are able start a three mismatch cord blood search:
- Step 1: run a two mismatch cord blood search, before you can start a three mismatch search
- Step 2: run a three mismatch cord blood search before you can start a four mismatch cord blood search
What is important to know about three and/or four mismatch searches?
In the legacy version of Search & Match Service, no overall match probabilities calculations (P0, P1, P2) for cord blood results were available. The sorting was performed within the match class (i.e. 5/8. 4/8) based on the Total Nucleated Cell (TNC) or CD34+ cell counts (depending on what a search coordinator prefers). This has been implemented in the same way in the updated version of Search & Match Service using the Hap-E Search matching algorithm.
In the updated Search & Match Service the number of search results can be bigger, as the Hap-E matching algorithm returns more potential matched cord blood units and the service no longer limits a coordinator to only 2 000 search results. If you experience a high number of potential cord blood search results you can, for example, filter on the minimum TNC, minimum CD34+ or by selecting certain registries or mismatch locations.
How is sorting done of three and/or four mismatch searches?
Three and/or four mismatch cord blood search results do not have any match probabilities calculated, the results are currently sorted within their match class (e.g. 5/8, 4/8) only by TNC or CD34+. The Hap-E Search matching algorithm returns more potential cord blood units than the legacy Search & Match Service. Many of these “extra” cord blood units tend to be low probability options to be selected for a patient in need of a transplant, because these cord blood units have low HLA resolution typing or missing allele typing.
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In an effort to improve the search coordinator's experience when performing three and/or four mismatch cord blood searches, WMDA is currently developing has developed several features that should improve the efficiency of finding suitable cord blood units. These are:
- A filter for returning only donors/cord blood with typing at HLA-C (and/or DQB1). Scheduled for delivery Q4 2023.
- A filter on match class - a search coordinator can go directly to the 5/8 or 4/8 potential matches.Has been delivered
- A "score" based sorting method for three and/or four mismatch cord blood results (find details below). Delivered for Hap-E, currently under development for ATLAS.
- Match probability calculation for three and/or four mismatches (find details below). Currently under development, scheduled for delivery 2024 (ATLAS), not planned for Hap-E.
"Score" based sorting for three and/or four mismatch cord blood results (see option 3 in above paragraph) - interim solution
It is generally true that the better HLA-typed a stem cell source (donor/cord blood) is, the higher the probability of a potential match it is. As WMDA is currently not able to provide match probabilities on 3 and 4 mismatched cord blood searches, WMDA will be implementing an interim score based approach. Find below the explanation:
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Below you can find some examples.
Match probability calculation for three and/or four mismatches (see in paragraph above option 4) - long-term solution
WMDA aims to implement calculation of actual match probabilities, because this would provide a better way of ranking search results than by using the above mentioned "scored" ranking. It will however, require a lot of work to develop this feature, as it will impact core elements of the Hap-E Search matching algorithmalgorithms. This therefore needs to be done with great care and will be thoroughly tested in order to make sure no part of the Hap-E Search algorithm algorithms is accidentally broken as a result of the added functionality.
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