A new study led by Antonio Jimenez Jimenez, M.D., associate professor at the Sylvester Comprehensive Cancer Center of the University of Miami Miller School of Medicine, has shown that stem cell transplants may soon become accessible to a broader range of patients. The research focuses on expanding donor compatibility for those with blood cancers, particularly benefiting individuals from diverse backgrounds who have historically faced challenges in finding suitable donors.
Jimenez Jimenez, a senior author and physician-scientist at Sylvester, presented early findings from this study at the 2024 European Hematology Association annual meeting. The latest results will be discussed at the 2025 American Society of Hematology (ASH) annual meeting in Orlando and highlighted in an ASH press briefing.
"We're rewriting the rules of what's possible for stem cell transplantation," said Jimenez Jimenez. "For patients who once faced impossible odds, this research opens the door to hope."
Traditionally, successful transplants required nearly perfect genetic matches between donor and recipient. This limited options for many patients, especially those of non-European ancestry; currently only about 29% of Black patients can find a fully matched donor compared to 89% among non-Hispanic white patients.
The ACCESS study, sponsored by the National Marrow Donor Program (NMDP), used post-transplant cyclophosphamide (PTCy) as part of a protective regimen that allows for safe transplants from unrelated donors mismatched at two or more HLA markers. This change could make suitable donors available to almost all patients needing transplants.
"By expanding the criteria for donor matching, we're making transplants accessible to nearly everyone, regardless of their ethnic background," said Jimenez Jimenez. "This could be a major step forward for cancer care."
The trial included 268 adults with blood cancers who received peripheral blood stem cell grafts from unrelated donors aged 35 or younger. Of these, 183 had seven out of eight HLA markers matched and 85 had four to six matches.
Outcomes showed similar one-year survival rates between groups with different levels of matching. Rates of acute grade II–IV graft-versus-host disease (GVHD) were also comparable—34% in the more mismatched group versus 39% in the less mismatched group after six months—and chronic moderate-to-severe GVHD rates were low: 8% and 11%, respectively, after one year. Notably, among recipients with greater mismatch, 61% identified as other than non-Hispanic white.
"We're seeing outcomes that rival those of fully matched donors, even in patients who previously had little chance of finding a match," said Jimenez Jimenez. "That's transformative for our field and for our patients."
Cyclophosphamide acts after transplant to reduce immune complications like GVHD by targeting cells most likely to cause problems. According to researchers, this approach makes it possible to consider donors previously seen as unsuitable due to lower genetic compatibility.
"Cyclophosphamide has changed the landscape of transplantation and donor utilization trends" said Jimenez Jimenez. "It allows us to safely use donors who would have been considered unsuitable just a few years ago."
While these findings are promising, further research is needed since the ACCESS trial was not randomized and optimal dosing strategies—especially for children—are still being investigated. Researchers estimate that almost all patients could now find suitable donors through international registries if these methods are adopted widely.
"We're committed to refining these strategies and ensuring that every patient-regardless of background-has a chance at a cure," said Jimenez Jimenez.
