Cord Blood Transplants: Can Two Be Better Than One for Leukemia?
"New research sheds light on how double cord blood transplants can significantly improve survival rates in children and young adults battling leukemia, especially when minimal residual disease is present."
Umbilical cord blood (UCB) transplantation has emerged as a viable alternative to traditional stem cell sources for patients with acute leukemia (AL) lacking an HLA-identical donor. The premise was simple: more hematopoietic stem cells translate to better outcomes. This led to the exploration of double-unit UCB transplants. However, initial results from prospective randomized studies painted a mixed picture, with double-unit transplants not always improving overall outcomes compared to single-unit transplants when an adequate cell dose was present.
A crucial factor in predicting the success of HSCT is the presence of minimal residual disease (MRD) before transplantation. MRD refers to the small number of cancer cells that remain in the body after treatment. Recent research suggested that in patients with positive pre-transplantation MRD, UCBT may offer a survival advantage compared to HLA-matched or HLA-mismatched unrelated donor transplantation. The question remained: Could these promising results be replicated in larger, prospective studies, and how does MRD status influence the effectiveness of single versus double-unit UCBT?
A recent study, published in Biology of Blood and Marrow Transplantation, delves into this question. Researchers analyzed data from a French prospective randomized study comparing single-unit and double-unit UCBT in children and young adults with acute leukemia. The primary goal was to determine how pre-transplantation MRD status affects leukemia relapse and survival rates in both single and double-unit UCBT settings.
Cord Blood Transplants Are Becoming More Valuable Than Ever
Cord blood transplants work much like bone marrow transplants: a person with leukemia, for instance, might have his or her own cancerous blood cells wiped out with chemotherapy and radiation before receiving a new supply of stem cells. At the same time, registry data show growth in the numbers of marrow donors and cord blood units, and the genetic variability of the registry is improving all patients' chances of finding the match they need. Umbilical cord blood is being increasingly used for hematopoietic stem cell transplantation and has been associated with a reduced incidence of severe graft-versus-host disease.
How Cord Blood Is Collected, Stored, and Used
An umbilical cord blood transplant is a type of allogeneic transplant that uses blood taken from the placenta and umbilical cord after a baby is born, and this small volume of cord blood contains a high number of stem cells. When a donated cord blood unit meets the standards for transplant, it is tissue typed, frozen and stored in a liquid nitrogen freezer at a public cord blood bank, after which it is listed on the registry so it can be found by searching patients. Standardized protocols for collection, processing, and storage allow healthcare providers to confidently utilize cord blood for transplantation.
From 1988 to Today: The Milestones That Started It All
The first successful cord blood transplant between a related donor and recipient was performed in Paris, France, in 1988 on a young boy with the blood disorder Fanconi's Anemia, whose newborn sister served as the donor (sources differ slightly on the boy's exact age). During the late 1980s, despite a growing number of volunteer bone marrow donors, the number of people able to find a suitable donor remained small compared to the need, which helped push cord blood into view as a new source of cells for transplant. Later research reported that using two cord blood units for one transplant resulted in improved rates of engraftment and survival in adults, planting the seed for the double-unit approaches explored today.
Decoding the Cord Blood Transplant Study
The study included 137 children and young adults undergoing UCBT, focusing on 115 patients with available data on MRD assessment performed just before the start of their pre-transplantation conditioning regimen. MRD positivity was defined as a level of ≥10-4, which was the case for 43 of the 115 patients. The research team then meticulously tracked survival rates, relapse risks, and disease-free survival over a three-year period.
- Double-unit UCBT may reduce relapse risk in MRD-positive patients.
- The benefits of double-unit UCBT are most pronounced in patients not treated with ATG.
- MRD status does not significantly impact survival rates overall.
- UCBT continues to be a promising option, even when MRD is present.
Making More From Less: Expansion Techniques and New Match Advantages
A large body of clinical and scientific data has been generated since the first cord blood transplantation was performed in 1989, according to a comprehensive review of adult cord blood transplantation. Cord blood transplantation can help patients with blood cancers or other blood diseases who need a stem cell transplant but who lack a close donor match, especially multiethnic patients, because stem cells in cord blood do not have to be as stringently matched to be safe. Researchers have also reported that expanding cord blood in the lab before transplant speeds establishment of a new blood supply in patients, reducing the high-risk time to recovery, with platelets and white blood cells engrafting more quickly than in a standard double-cord transplant.
The Pushback: Slow Engraftment, Rival Graft Sources, and Open Questions
One reason cord blood use has declined is that haploidentical transplantation has increased at the same time, yet there are not many studies directly comparing both hematopoietic stem cell sources in terms of clinical efficacy. Analyses of cord blood versus haploidentical transplantation have also noted unfavorable results driven by high morbidity and mortality in patients, with one commentary arguing that cord blood/patient pair transplants hardly improves long-term clinical outcome. On the other side of the ledger, a lab technique that multiplies the stem cells in a single cord blood unit before it is transplanted has moved from a research concept to an FDA-approved therapy with expanding uses, giving cord blood a real, approved answer to its biggest limitation.
Cord Blood Versus Bone Marrow: Trade-Offs in Recovery, GVHD, and Cost
Umbilical cord blood is an alternative graft source for patients without matched related donors, but allogeneic hematopoietic cell transplantation is a complex and costly procedure, and the costs of cord blood HCT have not been described in detail. Compared with bone marrow, cord blood transplants show slower initial recovery, with neutrophil recovery taking 19-27 days, and a higher risk of early infections, yet a lower risk of chronic graft-versus-host disease (33% versus up to 71% for bone marrow). Cord blood is ready for immediate use and tolerates genetic mismatches better than bone marrow, which helps explain its ongoing role as an alternative graft source.
The Future of Cord Blood Transplants
This study underscores the potential of UCBT as a curative strategy for children and young adults battling acute leukemia, even when MRD is present before transplantation. The findings suggest that a double-unit approach may enhance the graft-versus-leukemia effect, leading to improved survival rates, especially in MRD-positive patients who do not receive ATG as part of their conditioning regimen. As research continues to refine transplant strategies and identify optimal patient selection criteria, UCBT holds promise for transforming the landscape of leukemia treatment and improving outcomes for younger patients.
What the Data Say About Double-Unit Transplants
Umbilical cord blood transplantation is an important alternative stem cell source for both children and adults with haematologic malignancies, in part because cord blood units are rapidly available and have less stringent human leucocyte antigen matching requirements. Cord blood transplantation is largely used to treat children affected by haematological malignant disorders, and one prospective phase 2 multicenter trial studied outcomes of unrelated donor cord blood transplantation in 191 children with hematologic malignancies (median age 7.7 years) enrolled between 1999 and 2003, with a median follow-up of 27.4 months. These experiences sit at the heart of the question of whether two units can outperform one for patients with leukemia.
Expanding Uses and a Growing Banking Market
Cord blood contains stem cells that can be used to treat hematological, metabolic, immune and genetic disorders, and cord blood transplantation offers another method of definitive therapy for infants, children, and adults with certain hematologic malignancies, hemoglobinopathies, severe forms of T-lymphocyte and other immunodeficiencies, and metabolic diseases. In parallel, the cord blood banking services market has continued to expand, with players such as Cord Blood Registry (CBR), FamiCord AG, Shandong Cord Blood Bank, and ViaCord holding the largest market share, driven by increased investments and strategic initiatives including new service launches, collaborations, and partnerships.
Lifesaving for Patients Who Lack a Close Match
Umbilical cord blood and bone marrow transplants are curing or slowing the progression of many cancers originating in the bone marrow, such as leukemia and myeloma, as well as cancers of the lymphatic system such as lymphoma. Because cord blood is rich in immature cells, called stem cells, that generate developing and mature blood cells, it can substitute for marrow in a transplant, and the tissue-type match between donor and recipient does not need to be as close as in bone marrow transplants, a benefit especially important for patients who lack a close donor match, including multiethnic patients. Researchers are also investigating early predictors of success, such as whether hematopoietic chimerism measured 14 days after transplantation can predict engraftment following a cord blood transplant.
A Life-Saving Treatment That Is Normally Thrown Away
The modern story of cord blood transplantation is rooted in individual patients, such as Matthew, whose case presented the perfect circumstance to test whether cord blood could be used as a donor for transplantation. Duke opened its transplant program in 1990 and, in 1993, performed the first unrelated cord blood transplant in the world for a 4-year-old boy with leukemia. Because this life-saving treatment is normally thrown away, advocates continue to spotlight its potential for treating leukaemia patients, while researchers keep comparing real-world outcomes of umbilical cord blood versus HLA-haploidentical transplantation against what randomized trials predict.