Cord blood is the blood that remains in the umbilical cord and placenta following birth, and it is a rich source of hematopoietic stem cells. Leukemia is a form of cancer affecting blood-forming tissues. The stem cells within cord blood have become a significant resource in the treatment of certain leukemias. Since the early 1990s, these cells have been used to cure both children and adults.
How Cord Blood Treats Leukemia
The therapeutic potential of cord blood lies in its high concentration of hematopoietic stem cells (HSCs). For individuals with leukemia, treatment often involves aggressive chemotherapy and radiation to eradicate cancerous cells. This approach also destroys the patient’s healthy bone marrow, leaving them unable to generate their own supply of red blood cells, white blood cells, and platelets.
Following treatment, the cord blood stem cells are infused into the patient. These HSCs migrate to the bone marrow, where they begin a process called engraftment. During engraftment, the donor stem cells establish themselves and start to produce new, healthy blood cells, rebuilding the patient’s blood and immune systems. This repopulation is known as hematopoietic reconstitution.
This newly formed immune system offers a secondary benefit. The new immune cells can recognize and eliminate any leukemia cells that may have survived the initial chemotherapy or radiation. This phenomenon, where the transplanted cells help to fight the cancer, is referred to as the graft-versus-leukemia effect, which can reduce the likelihood of the cancer returning.
The Cord Blood Transplant Process
The transplant process begins with a conditioning regimen. Before receiving the new stem cells, the patient undergoes high-dose chemotherapy and, in some cases, radiation therapy. This intensive treatment has a dual purpose: to eliminate the existing leukemia and to suppress the patient’s immune system to prevent rejection of the transplanted cells.
Once conditioning is complete, the cord blood is infused. The cryopreserved cord blood unit is carefully thawed. The infusion process resembles a standard blood transfusion, with the cells delivered into the patient’s bloodstream through an intravenous (IV) line. The entire procedure is closely monitored.
The period following the infusion is centered on engraftment. During this time, which can span several weeks, the patient is under constant medical supervision. Patients are particularly vulnerable to infections during this phase because their immune system has yet to recover, necessitating a protected environment and careful management.
Sources of Cord Blood for Transplant
Cord blood for transplantation is acquired from two types of banks. Public cord blood banks function similarly to general blood banks, relying on altruistic donations. Parents can choose to donate the cord blood after birth. The collected cord blood is then tested, processed, and cryogenically frozen, with its tissue type listed on a registry for any matching patient who needs it.
In contrast, private cord blood banks offer a fee-based service for families. Parents can pay to have their newborn’s cord blood collected and stored exclusively for their own family’s potential future use. This type of transplant is known as an autologous (using one’s own cells) or a related-donor transplant.
A significant consideration arises when treating childhood leukemia. It is rare for a child’s own stored cord blood to be used for their own treatment. The genetic mutations that cause childhood leukemia are often present at birth. Consequently, these same mutations would exist within the child’s own cord blood, making it unsuitable for transplant as it would reintroduce the cancerous cells. This is an important factor for parents deciding between public donation and private banking.
Comparing Cord Blood to Other Stem Cell Sources
When considering a stem cell transplant, cord blood is one of several options, alongside bone marrow and peripheral blood stem cells (PBSC). One advantage of cord blood is its immediate availability. Since cord blood units are collected at birth and stored in banks, they can be accessed quickly. This contrasts with bone marrow donation, which involves finding a suitable donor and coordinating a surgical collection procedure.
Cord blood also offers more flexibility in tissue matching. The standard for matching is based on human leukocyte antigens (HLA), which are proteins on the surface of cells. Cord blood transplants do not require a perfect HLA match to be successful, unlike bone marrow transplants. This expands the pool of potential donors, which is helpful for patients from diverse ethnic backgrounds who often have difficulty finding a matched adult donor.
A notable limitation of cord blood is the relatively low number of stem cells in a single unit. This “cell dose” may not be sufficient to ensure successful engraftment in larger adolescents or adults. To overcome this, a common strategy is to use two separate cord blood units for a single transplant. This approach, known as a double cord blood transplant, increases the total number of infused stem cells.
The immunological properties of cord blood also present a distinct advantage. The immune cells in cord blood are considered more naive or immature compared to those from an adult donor. This immaturity means they are less likely to cause severe graft-versus-host disease (GVHD), an attack against the recipient’s body tissues. As a result, patients receiving cord blood transplants generally experience a lower risk and reduced severity of GVHD.