New results from the Phase II ACCESS trial represent a significant milestone in solving one of transplant medicine’s biggest challenges: finding a donor for every patient in need of a blood stem cell transplant

One-year overall survival exceeds 80% among trial participants receiving 4/8-7/8 mismatched unrelated donor transplant

Ninety-nine percent of patients with common blood cancers can find a suitable donor and safely and effectively access transplant

New research from NMDP, a global nonprofit leader in cell therapy, and conducted by CIBMTR® (Center for International Blood and Marrow Transplant Research®) at the 67^th American Society of Hematology (ASH) Annual Meeting and Exposition in Orlando, Fla., demonstrates that patients receiving allogeneic transplantation using more deeply mismatched unrelated donors (MMUD), followed by post-transplant chemotherapy, can achieve outcomes comparable to those receiving transplants from more closely, but still not fully, matched donors. The data also show that virtually every patient searching international registries now has a greater than 99% likelihood of identifying a suitable blood stem cell donor. Notably, ASH selected this abstract for presentation at its 2026 Highlights of ASH® program in January.

While exact donor-patient genetic matching was historically considered essential for preventing life-threatening complications after transplant, results from the NMDP-sponsored ACCESS study [#936] showed strong, consistent outcomes among adults receiving donor grafts across all mismatch levels (4/8–7/8). At one-year post-transplant, overall survival (OS) exceeded 80% across all match levels, achieving a significant 86% for <7/8 mismatches and 79% for 7/8 mismatches.

“We are fundamentally changing what’s possible in transplant medicine and creating a new standard of care for curing common blood cancers,” said Steven M. Devine, M.D., chief medical officer, NMDP, and executive lead, CIBMTR. “For the first time, we have clear evidence that patients can safely receive a range of mismatched unrelated donor grafts and achieve survival outcomes on par with those from fully matched donors—this is a giant leap forward for transplant science and medicine.”

The most important factor that determines donor-recipient compatibility in unrelated donor transplantation is matching at human leukocyte antigens (HLA), the proteins that help the immune system distinguish its cells from another’s. When HLA mismatch occurs, the donor’s immune system can recognize the patient’s tissues as foreign, triggering graft-versus-host disease (GVHD), a potentially life-threatening complication.

Historically, achieving an 8/8 HLA match resulted in the best transplant outcomes, while using donors with fewer matching alleles (<7/8) was associated with poor survival and higher rates of GVHD. However, NMDP research published in the Journal of Clinical Oncology in June demonstrated that patients receiving <7/8 matched graft achieved outcomes comparable to, or even exceeding, historical 8/8 benchmarks of 75% survival—supporting broader donor eligibility.

Finding a fully or closely matched donor remains a major barrier for many patients, as HLA markers are inherited. If there are no suitable matches within the family, physicians must search international registries, now totaling more than 42 million potential donors and more than 760,000 cord blood units. Unfortunately, patients of non-European ancestry have historically had much lower chances of finding a suitable donor.¹

ACCESS trial demonstrates safe and effective use of MMUDs

Presenting author Antonio Jimenez-Jimenez, M.D. will deliver the oral presentation on Monday, Dec. 8, at 4 p.m. EST sharing detailed results from ACCESS (NCT04904588). This prospective, multicenter trial evaluated 268 adult patients with common blood cancers who received 4/8 to 7/8 HLA-MMUD peripheral blood stem cell (PBSC) grafts with post-transplant cyclophosphamide (PTCy). While prior studies explored PTCy for GVHD prevention in related individuals with HLA mismatches, the ACCESS trial is the first to evaluate this approach in patients receiving PBSC transplants from unrelated donors with as few as 4/8 HLA matches. Notably, 61% of participants in the <7/8 cohort self-identified as other than non-Hispanic White.

“These results challenge long-held assumptions about the risks of HLA mismatching and demonstrate that PTCy-based regimens can safely extend donor eligibility to nearly all patients in need of transplant, including those from varied backgrounds who are most in need of a suitably matched donor,” said Dr. Jimenez-Jimenez, associate professor of medicine in the division of Transplantation & Cellular Therapy at Sylvester Comprehensive Cancer Center, at the University of Miami Miller School of Medicine.

Non-relapse mortality (7/8=13.7%; <7/8=8.4%), relapse (7/8=17.1%; <7/8=22.8%), and moderate-to-severe chronic GVHD (7/8=11.3%; <7/8=7.7%) rates were similarly favorable between cohorts, regardless of conditioning regimen.

An additional CIBMTR analysis included in the presentation depicted the ACCESS results within the context of current donor availability on international registries. For patients highly unlikely to find an 8/8 match, allowing a <7/8 match offers a significantly higher pool of potential donors available, even if these patients had ethnically diverse backgrounds. Sixty-two percent of patients included in this five year analysis were ethnically diverse, and the median number of available donors increased from two at the 7/8 level to 83 at the 6/8 level, illustrating the profound impact of broadening acceptable match levels.

Donor for All: Research advances outcomes and access for all patients

NMDP’s Donor for All initiative unites clinical research, data science and operational innovation to close long-standing gaps in access for patients, especially for those of diverse ancestry. The ACCESS, OPTIMIZE (NCT06001385) and ACCELERATE (NCT06859424) trials are key Phase II trials at the core of the Donor for All initiative; additional ACCESS findings and in-progress updates from ACCELERATE will be presented at ASH, including:

• Results from the reduced-intensity conditioning (RIC) cohort [#4232] of the ACCESS study in a poster presentation. Findings demonstrated one-year OS at 79.6% and relatively low rates of non-relapse mortality (12.5%), chronic GVHD (15.6%) and severe GVHD (3.7%) across HLA match levels. Results confirmed that PTCy-based MMUD transplantation delivers consistent and reproducible outcomes across conditioning intensities and centers, further supporting its use as a safe and scalable approach to expand donor access.
• A poster presentation of the ACCESS PRO (“Living the Recovery”) [#6042] will also show findings that complemented these positive clinical outcomes. The study examined patient-reported outcomes to better understand survivorship and quality of life one year after transplant. Among 268 patients, self-reported quality-of-life scores, physical function and fatigue returned to or exceeded baseline levels, with overall results comparable to population norms. Financial well-being also remained stable from baseline to one year. Patients who experienced moderate or severe chronic GVHD reported greater symptom burden and reduced physical function, underscoring the importance of continued efforts to reduce GVHD incidence and strengthen supportive care strategies.
• Another poster presentation will show the latest from the in-progress ACCELERATE trial, [#6035] which represents the next step in optimizing transplant. This multicenter platform protocol will evaluate multiple PTCy-based GVHD prevention regimens—testing reduced-dose PTCy with novel agents such as abatacept and ruxolitinib—across up to 60 U.S. centers. The goal: to refine efficacy, minimize toxicity and further improve long-term outcomes for patients receiving mismatched donor transplants. ACCELERATE is still enrolling at sites across the U.S.

“These collective studies move us closer to a future where donor match limitations no longer determine who receives a cure,” said Dr. Devine. “With donor matching no longer as restrictive, clinicians can now prioritize other factors, such as donor age and cell quality, to optimize outcomes and further individualize transplant care. Through our Donor for All initiative, NMDP is combining rigorous science with a commitment to equity so that every searching patient, regardless of ancestry, can find their cure.”

Additional studies presented at ASH 2025

Other research presented by NMDP and CIBMTR at ASH further support the organizations’ aim to make safe and effective cell therapy available to every patient in need.

In an oral presentation to be presented Sunday, Dec. 7 at 10:30 a.m., Kai Yu, Ph.D., Fralin Biomedical Research Institute, Virginia Tech FBRI Cancer Research Center, will share results from the MEASURE Genome Atlas study [#455], which sought to advance understanding of the genomic landscape of acute myeloid leukemia (AML). Using whole genome sequencing (WGS) from 255 adult patients across 18 U.S. cancer centers, the study demonstrated that WGS can function as a single, comprehensive diagnostic platform for AML—reproducing 93% of standard prognostic markers while identifying additional alterations, including KMT2A partial tandem duplications and cryptic gene fusions missed by traditional testing. This comprehensive atlas of adult AML genomics provides novel insights into disease biology, creates an evidentiary basis to support clinical testing improvements, and is a resource for both diagnostic and drug development. NMDP supported this study, with CIBMTR facilitating the research.

Other notable presentations include:

• Longer telomeres in donors aged ≤35 years reduce graft failure and non-relapse mortality after allogeneic HCT (oral)—Found that longer telomeres in younger donors correlated with reduced graft failure and non-relapse mortality.
• Impact of HLA alloimmunization on availability of HLA well-matched and mismatched unrelated allogeneic hematopoietic cell donors for transplantation (DSA match) (poster)—Examined how donor-specific antibodies affect donor match feasibility and clinical outcomes.
• Vδ2 unconventional T cells in the donor graft are associated with improved overall survival after unrelated donor allo-HCT for AML and MDS: An analysis from the DKMS and NMDP Graft Composition Study (oral)—Demonstrated that higher frequencies of Vδ2 T cells in donor grafts are associated with improved survival after unrelated donor transplantation.

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 630,000 people who have received hematopoietic cell transplantation and other cellular therapies. Learn more at cibmtr.org.

About NMDP^SM

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.

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