Cell Sources

Many factors can enter into the clinical decision of selecting the hematopoietic cell source that is best for each patient. Several recent studies have shown that comparable allogeneic transplant outcomes are achieved regardless of hematopoietic cell graft used. [1,2,3,4] View outcomes by cell sources in related and unrelated donor transplantation, also showing comparable transplant outcomes, regardless of graft source.

Marrow

Bone marrow has been a standard source of hematopoietic cells for more than 40 years. Transplant physicians may select marrow because:

• Chronic graft-versus-host disease (GVHD) is lower and less severe than in PBSC transplants [2]
• For pediatric patients undergoing allogeneic transplant, survival rates are higher for marrow than PBSC [5]

PBSC

For allogeneic transplants, PBSC is used more often than marrow for adult patients. Physicians may select PBSC based on:

• Faster neutrophil and platelet recovery [2]
• Faster immune reconstitution [2]

Autologous transplants in both pediatric and adult patients rely almost exclusively on PBSC rather than bone marrow. Reasons include:

• Easier collection of cells
• More rapid hematopoietic recovery
• Easier graft manipulation (e.g., CD34+ cell selection, tumor cell purging) [6]

Umbilical Cord Blood

Physicians may consider umbilical cord blood for patients who need an unrelated donor and have an uncommon HLA type (making it difficult to identify a full match), or are in urgent need of a transplant. Transplant physicians may select cord blood because:

• HLA mismatch is better tolerated [7]
• Cord blood is available more quickly than marrow or PBSC unrelated donors [7]
• Reduced incidence and severity of acute GVHD [7,8]

Umbilical cord blood transplants are used more often for pediatric patients, but cord blood use has grown in both adult and pediatric populations. [9]

The Blood and Marrow Transplant Clinical Trials Network (BMT CTN) conducted a large, phase III clinical trial to determine whether there were differences in patient outcomes and/or donor experiences between PBSC and marrow in unrelated donor transplants and incidence of GVHD. [2]

The study found that PBSC and bone marrow transplant recipients had comparable two-year survival: 51% vs. 46%, respectively (p=0.29). However, the incidence of chronic GVHD at two years was higher in patients who received PBSC compared with those who received marrow: 53% vs. 41%, respectively (p=0.01). Chronic GVHD was also more severe in recipients of PBSC grafts. The overall incidence of graft failure in the PBSC group was significantly lower compared to the incidence in the bone marrow group: 3% vs. 9%, respectively (p=0.002).

Use of Cord Blood in Pediatric Transplantation

In 2022, cord blood units were used in approximately 26% of pediatric transplants facilitated by NMDP/Be The Match. In comparison, approximately 4% of adult transplant recipients received umbilical cord blood in 2022.

Figure 2. Transplants by Cell Source, Pediatric Patients, 1990-2016

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Use of Cord Blood for People of Color

Because HLA mismatch is better tolerated in cord blood transplantation, the use of this stem cell source has been particularly beneficial for people of color who have traditionally had more difficulty finding a suitably matched marrow or PBSC donor on volunteer donor registries.

Figure 3. Role of Cord Blood in Transplants by Ethnic Background

Use of Cord Blood in Adult Patients

Transplant physicians are developing ways to overcome the limited cell dose of an umbilical cord blood unit to permit more cord blood transplants in larger adults. Using two or more umbilical cord blood units to increase the cell volume is an option for some adult patients. [7] In 2022, 21% of cord blood transplants facilitated by the NMDP/Be The Match used more than one umbilical cord unit.

Other methods being developed include the co-infusion of mesenchymal cells or PBSC, and ex vivo expansion of cord blood cells prior to infusion. [8]