Umbilical cord blood, collected from the umbilical cord and placenta after birth, is a rich source of blood-forming stem cells. Leukemia is a cancer that affects the body’s blood-forming tissues, including the bone marrow. For individuals with specific types of leukemia, cord blood is a valuable treatment resource. Its use in transplants offers a therapeutic path for patients, as the stem cells can restore the body’s ability to produce healthy blood cells following aggressive cancer treatments.
The Role of Stem Cells in Leukemia Treatment
Primary treatments for leukemia, like high-dose chemotherapy and radiation, are designed to eliminate cancerous cells. A consequence of these therapies is the destruction of the patient’s healthy bone marrow, including the hematopoietic stem cells responsible for generating new blood cells. Without these stem cells, the body cannot produce the red blood cells, white blood cells, and platelets needed for survival.
A cord blood transplant introduces new, healthy hematopoietic stem cells from a donor into the patient’s body. These infused cells are not a direct attack on the cancer but a “rescue” for the blood-producing system. The donor stem cells migrate to the empty bone marrow to begin producing new, cancer-free blood cells.
The process of new stem cells establishing themselves in the bone marrow to create blood cells is known as engraftment. This is the foundational step in rebuilding the patient’s blood and immune system. The transplant’s success hinges on these new cells taking hold and multiplying to restore normal blood function.
The Cord Blood Transplant Procedure
The initial stage of a transplant is the conditioning regimen, which prepares the body to receive the new stem cells. During this period, the patient undergoes high-dose chemotherapy and sometimes radiation to eradicate remaining leukemia cells. This also suppresses the immune system to prevent rejection of the transplant and can be physically demanding.
Following conditioning, the cord blood infusion takes place. The cryopreserved cord blood unit is thawed and infused into the patient’s bloodstream through a central venous catheter, a process similar to a blood transfusion. For some adult patients, the cell count in a single unit may be insufficient, necessitating the infusion of two separate units.
The post-transplant recovery period begins immediately after the infusion. The patient remains in the hospital under close observation as their body accepts the new stem cells. Medical teams monitor for the first signs of engraftment, when the donor cells start producing new blood cells. This phase has a heightened risk of infection, as the patient’s immune system is severely compromised.
Sourcing and Matching Cord Blood
Cord blood is sourced through two types of banking systems. The first is public cord blood banking, which operates on an altruistic model. Parents can donate their newborn’s umbilical cord blood at no cost, and these donations are stored and listed on international registries, making the unit available to any matching patient worldwide.
The alternative is private cord blood banking, where parents pay a fee to store their baby’s cord blood for their own family’s potential use. For treating leukemia, a transplant from a donor (an allogeneic transplant) is preferred over using the patient’s own cells (autologous). This is because a child’s own cord blood may contain the same genetic mutations that led to the leukemia.
The matching process is centered on Human Leukocyte Antigen (HLA) typing. HLAs are proteins on the surface of cells that the immune system uses to recognize which cells belong in the body. A close HLA match between the donor and recipient reduces the risk of complications. A key advantage of cord blood is that it does not require a perfect HLA match, unlike bone marrow, which expands the potential donor pool for patients of diverse ethnic backgrounds.
Outcomes and Key Considerations
The clinical results of a cord blood transplant are influenced by several factors, and one is the cell dose. The number of stem cells in a single cord blood unit is fixed and relatively small, which can be a limitation for adult patients. To overcome this, a double cord blood transplant, using two different units, is sometimes performed to ensure enough cells are infused.
Another consideration is the speed of engraftment. The process of new blood cell production is slower with cord blood compared to stem cells from bone marrow. This delay can extend the period during which the patient has a weakened immune system, increasing their vulnerability to infections. Close monitoring and supportive care are required during this time.
A potential complication of any allogeneic transplant is Graft-versus-Host Disease (GVHD), a condition where the donor’s immune cells attack the recipient’s tissues. While GVHD can occur with cord blood transplants, the risk of severe chronic GVHD is lower compared to other stem cell sources. This is attributed to the immaturity of the newborn’s immune cells in the cord blood.