When a patient with a blood-related cancer needs a bone marrow transplant, there are four common donor sources: A matched related donor (a family member), a matched unrelated donor (from a donor database), a half-matched donor, or umbilical cord blood. The reason for this is that most patients with blood-related cancers were born with the genetic defect that triggered the cancer, they cannot use their own stem cells as a source for transplant. As with any approach, each has its pros and cons, but consensus has generally placed a matched sibling first, followed by a matched unrelated donor, with cord blood and half-matched donors reserved for patients without access to either of the first two options.

According to statistics only about one-quarter of the people who need an allogeneic (unrelated donor) transplant have a sibling who is a genetic match and able to donate stem cells. The other three-quarters need to find another donor for their transplant.

The test that’s used to identify appropriate donors is called HLA matching (human leukocyte antigen). HLAs are proteins that are present on most cells in your body. Your immune system uses HLAs to recognize which cells belong in your body. When using an adult donor, it’s important that the donor and the person undergoing the transplant have HLAs that match so the donor immune system doesn’t attack the patient’s normal tissues, a complication called graft-versus-host disease.

A person’s HLA type is inherited from their parents, which is why siblings offer the best chance of finding a match. People’s HLA type can be determined with a simple blood test or cheek swab. People of southern European, Asian, African, Hispanic, and Middle Eastern backgrounds tend to have more diverse HLA types. These types are less commonly found in adult volunteer donor registries. It can also be difficult for someone with a mixed background — for example, part Asian and part Hispanic — to find a donor who is a match. For them, cord blood transplants offer a good opportunity for a cure.

In the past 3 decades there have been more than 40,000 cord blood transplants performed internationally. These were mainly for leukemias, lymphomas and other blood-related disorders. Cord blood transplants offers a cure for blood related cancers in both children and adults.

Stem cell transplants with cord blood have been used to cure both children and adults with leukemia since the early 1990’s.

Why Cord blood for stem cell transplant may outperform a matched sibling donor:

A major benefit of cord blood is that the immune system of a newborn baby is not yet entirely developed. This means that the match that’s required between the cord blood stem cells and the person receiving them is less strict. Since umbilical cord stem cells are more “basic” than adult blood cells, they therefore need a lower level of matching than blood cells from an adult donor. Nevertheless, even though the cord blood immune system is very flexible, it can still develop into a healthy immune system. Cord blood cells are very good at combating cancer, this effect is called the graft-versus-leukemia and it can help prevent a person’s cancer from returning after their transplant.

The University of Colorado Cancer Center did an assessment of 190 patients getting cord-blood transplants versus 123 patients receiving transplants from the “gold standard” of matched sibling donors bone-marrow. Although the survival outcomes were the same between the two methods, considerably fewer complications were found in chronic graft-versus-host disease in patients receiving transplants from cord blood. The cord blood group also showed a slightly lower rate of relapse.

One challenge with cord blood cells is obtaining enough of these cells to perform a successful transplant, especially in adults.

To overcome this hurdle, double unit cord transplants from two different sources are transplanted.  The other alternative is to expand small samples of banked cord blood to the amount of stem cells needed for transplant.

All these above factors indicate that cord blood may even out-compete the gold standard of matched sibling donors.

Therefore, for people who don’t have a matched bone marrow or stem cell donor, a cord blood transplant may offer the best chance for being cured of blood cancer.

References:

• Gale KB et al. 1997; Backtracking leukemia to birth: Proc Natl Acad Sci USA. 94(25):13950-4.
• Janet D. Rowley 1998; Backtracking leukemia to birth: Nature Medicine 4:150-1.
• Ballen KK, Verter F, Kurtzberg J 2015; Bone Marrow Transplantation 50(10):1271-8.
• Filippo Milano, et al. 2016; Cord Blood Transplants Show Promise in Leukemia Treatment. NEJM 375:944-953.