Data published in Blood Advances show young, <7/8 mismatched unrelated donor one-year patient outcomes are similar to fully matched donors

New clinical trial results published today in the peer-reviewed journal Blood Advances show strong one-year outcomes for adult patients with blood cancers who received transplants with peripheral blood stem cell (PBSC) grafts from young, more extensively mismatched unrelated donors (MMUDs), when combined with a post-transplant cyclophosphamide (PTCy) graft-versus-host disease (GVHD) prevention strategy. Trial participants’ one-year overall survival rates exceeded 80% across all match levels, on par with those from fully matched donors.

Historically, blood stem cell transplants required an exact donor-patient match of eight human leukocyte antigen (HLA) markers, which are immune system receptors on cell surfaces used to assess donor-recipient compatibility and prevent life-threatening GVHD. These new results highlight patient outcomes for those who received donor cells with fewer matching HLA markers (4/8–6/8), alongside those with more closely matched donors (7/8), suggesting that physicians can safely select donors from a substantially broader pool, increasing access for patients from non-European ancestries who historically may not have found a fully matched donor.

“For many patients, particularly those with ethnically diverse ancestries, not having a fully matched donor used to mean they were ineligible for transplant, limiting their options and potentially a second chance at life,” said Steven Devine, MD, chief medical officer, NMDP^SM, and senior scientific director, CIBMTR^® (Center for International Blood and Marrow Transplant Research^®). “These findings are promising signals regarding what a donor search can mean for patients, bringing us one step closer to a future where virtually every patient needing a transplant can find a suitable donor through international registries.”

Historically, patients from ethnically diverse ancestries had much lower chances of finding a fully matched unrelated donor—as low as 29% for Black or African American patients and 48% for Latino and Hispanic patients versus 79% for non-Hispanic White patients. Prior modeling studies included in the paper suggest that inclusion of 6/8 MMUDs could increase donor availability to near-universal levels for all patients regardless of ancestry.

A 'Donor for All': Research widens access to transplant for more patients

Investigators from 36 U.S. transplant centers evaluated 268 adults with high-risk blood cancers in the NMDP-sponsored, CIBMTR-led ACCESS (NCT04904588) Phase II trial. Trial participants received a transplant using PBSC grafts from mismatched (4/8-7/8 HLA) donors with PTCy. The trial limited donors to ages 18–35, as previous CIBMTR research shows that younger donors provide better outcomes. Additionally, while prior studies explored PTCy for GVHD prevention in haploidentical (related) donors with HLA mismatches, ACCESS is the first multicenter study to evaluate this approach in patients receiving PBSC transplants from unrelated donors with as few as 4/8 HLA matches.

Key study findings:

• Among trial participants, 183 received 7/8 matched grafts and 85 received grafts matched at <7/8 (4/8–6/8). Most patients in the <7/8 cohort (82.4%) received a 6/8 matched graft.
• One-year overall survival was 79% among patients who received 7/8 matched grafts and 86% among the <7/8 cohort.
• GVHD-free, relapse-free survival after one year was 51.1% in the 7/8 group and 54.6% in the <7/8 cohort.
• Nearly two-thirds (63.5%) of participants in the <7/8 cohort self-identified as ethnically diverse.

The analysis included from a previous modeling study showed that among patients with ethnically diverse backgrounds with few fully matched options, the median number of potentially available donors rose from one at the 7/8 level to 33 at the 6/8 level. For patients identifying as non-Hispanic White, it rose from five to 195.

“These results challenge long-held assumptions about the risks of HLA mismatching and show that modern GVHD prevention approaches can significantly expand the donor pool for patients with blood cancers, especially those from varied backgrounds most in need of access to transplant,” said Antonio Jimenez Jimenez, MD, associate professor of medicine in the Division of Transplantation and Cellular Therapy at Sylvester Comprehensive Cancer Center, part of the University of Miami Miller School of Medicine, and lead author of the study. “While continued study across HLA mismatching will help further define long-term safety and efficacy, this evidence suggests that physicians may consider a broader range of donor options, including multiple mismatched donors, when evaluating transplant candidates, which could help reduce barriers to transplantation and shorten time to treatment.”

ACCESS furthers NMDP’s mission to save lives through cell therapy through its clinical research, data science and operational innovations that address long-standing barriers to transplant. NMDP is also sponsoring two other trials currently underway, including OPTIMIZE (NCT06001385) and ACCELERATE (NCT06859424), which are evaluating reduced-dose PTCy and other PTCy-based GVHD prevention strategies to mitigate complications and improve outcomes following suitably matched transplants.

About NMDP

At NMDP^SM, we believe each of us holds the key to curing blood cancers and disorders. As a global nonprofit leader in cell therapy, NMDP creates essential connections between researchers and supporters to inspire action and accelerate innovation to find life-saving cures. With the help of blood stem cell donors from the world’s most diverse registry and our extensive network of transplant partners, physicians and caregivers, we’re expanding access to treatment so that every patient can receive their life-saving cell therapy. NMDP. Find cures. Save lives. Learn more at nmdp.org.

About CIBMTR

CIBMTR^® (Center for International Blood and Marrow Transplant Research^®) is a nonprofit research collaboration between NMDP^SM, in Minneapolis, and the Medical College of Wisconsin^®, in Milwaukee. CIBMTR collaborates with the global scientific community to increase survival and enrich quality of life for patients. CIBMTR facilitates critical observational and interventional research through scientific and statistical expertise, a large network of centers, and a unique database of long-term clinical data for more than 750,000 people who have received hematopoietic cell transplantation and other cellular therapies. Learn more at cibmtr.org.

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