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In pursuit of a donor for all — expanding access with HLA mismatched unrelated donors

Finding a stem cell donor for every patient in need is a lofty goal. Even with more than 39 million volunteer donors listed worldwide, a fully HLA matched (8/8 at HLA-A, B, C and DRB1) donor is not available for all patients. People of color are much less likely than non-Hispanic white people to have a fully matched donor available. Donor recruitment alone is unlikely to fully close this gap. 

That’s why findings from a recent study by the Center for International Blood and Marrow Transplant Research Center (CIBMTR), a research collaboration between the National Marrow Donor Program/Be The Match (NMDP/BTM) and the Medical College of Wisconsin, bring such good news — that no patient, regardless of racial/ethnic background, must go without a donor.

Ideal world vs. reality

In the ideal world, every patient would have either a fully matched related or unrelated donor. The reality is that African American patients have only a 29% likelihood of finding an 8/8 unrelated donor on the NMDP/BTM registry. That’s where mismatched unrelated donors (MMUD) come in.

Enter MMUD

Recent clinical trials and studies have shown that use of MMUD is safe and effective for 7/8–4/8 match levels using post-transplant cyclophosphamide (PTCy) or 7/8 using abatacept-based graft vs host disease (GVHD) prevention strategies. These approaches expand donor choice and, importantly, expand access to people from underrepresented groups. 

99%+ donor availability for all

The study team used registry modeling approaches to evaluate the likelihood of finding a suitable donor in the NMDP/BTM donor registry for people in 21 racial/ethnic groups. When allowing for match levels down to 5/8, researchers found that the availability of a donor was more than 99% for all racial/ethnic groups. The availability rate remained greater than 99% even when considering additional donor characteristics, such as younger donor age (under the age of 35). That’s a substantial improvement over the 29% likelihood African American patients face when looking for an 8/8 unrelated donor. 

The importance and promise of the potential for safe and effective use of MMUD cannot be overstated in terms of meeting the donor needs of every patient in need of a stem cell transplant. 

Learn more by reviewing a comprehensive analysis and description of the study.

View Infographic


Abu Chowdhury
Martin Maiers
Stephen Spellman
Yung-Tsi Bolon
Steven Devine