For both children and adults suffering from leukemia, cord blood stem cells offer the potential for a life-saving transplant. Recent research also suggests that cord blood stem cells offer better survival outcomes for certain leukemia patients than those from bone marrow or peripheral blood sources [*]. Here’s what to know:
What Is Leukemia?
Leukemia is a cancer of the blood marked by an abnormal profusion of immature white blood cells in your bone marrow, the spongy tissue where the body’s blood cells are made.
The word leukemia comes from the Greek leukos (white) and haima (blood). Leukemia cells crowd out healthy blood cells, which ordinarily include red blood cells that carry oxygen throughout your body, white blood cells that fight infection, and platelets that help your blood clot.
Mature blood cells are generated by hematopoietic stem cells (HSCs), which are capable of differentiating into myeloid or lymphoid blood cells — the building blocks of the body’s blood and immune systems. Myeloid cells become red blood cells, platelets, and certain white blood cells (basophils, eosinophils, and neutrophils), while lymphoid cells develop into certain white blood cells called lymphocytes and natural killer (NK) cells that fight infection.
Many blood cells are short-lived and need to be replenished constantly. The average person needs around 100 billion new blood cells each day, and HSCs are the only source of all these cells [*].
Types of leukemia include acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), and chronic myeloid leukemia (CML) [*]. Some forms of leukemia develop more often in adults; white males aged 65-74 are most at risk. Leukemia accounts for 3.2% of all new cancer cases in the U.S. and is the 10th most common cancer [*].
What Is Cord Blood?
Cord blood is harvested from the blood and tissue of the umbilical cord right after the birth of a baby. Once discarded as medical waste, cord blood was found in the 1980s to be a rich source of hematopoietic stem cells (HSCs) used in life-saving stem cell transplants.
There are more than 80 FDA-approved cord blood stem cell treatments for a wide range of blood disorders, cancers, immune disorders, and metabolic diseases. More than 85,000 cord blood stem cell transplants have been performed worldwide for a variety of malignant and non-malignant disorders [*].
Can Cord Blood Cure Leukemia?
Yes, cord blood transplants can treat leukemia in both children and adults and in many cases keep it from recurring.
A 4-year-old boy with T-cell leukemia received the first cord blood stem cell transplant using an unrelated donor’s cord blood in 1993. In the next 2 years, 25 more transplants were performed, and the success of these seminal transplants led to the establishment of the first public cord blood bank [*]. Today, roughly 5 million cord blood units are banked worldwide, with about 800,000 in public banks and the remaining in private or family banks [*].
Cord blood transplants may be a suitable treatment for blood cancers that are not likely to be cured by chemotherapy alone. They’re used for a number of conditions in which the patient cannot make their own healthy blood cells, including aplastic anemia and genetic disorders affecting blood, bone marrow, and immune system disorders [*].
Types of Cord Blood Transplants for Leukemia
The types of cord blood transplants are identified by the donor source and the level of HLA matching required.
Autologous transplant: Uses the patient’s own stem cells.
Allogeneic transplant: Uses stem cells from a donor that meet the matching requirements.
Syngeneic transplant: Uses stem cells from an identical twin.
Haploidentical transplant: Uses stem cells that match only half the HLAs — typically, from an immediate family member (parent or sibling).
How Are Stem Cells Used to Treat Leukemia?
Stem cell transplant is typically an arduous process for patients with a long recovery, but for many, it is the only option for survival. Here are the key steps:
1. Locate matching stem cells
For leukemia, stem cells must be located that provide as close a match as possible to the patient’s HLA (human leukocyte antigen) type.
HLAs are proteins present in almost every cell and are programmed by our DNA to recognize compatible proteins and attack foreign ones. They’re what cause your immune system to attack viruses and bacteria.
There are some transplants that can use the patient’s own stem cells but if the disease has a genetic component, doctors will need to use a donor source. For leukemia, the gold standard is a perfectly matched sibling.
Two siblings have a 25% chance of being a perfect match, a 75% chance of being a suitable match and a 25% chance of not matching at all. The likelihood of a perfect match goes up to 44% for patients with two siblings, 58% for those with three, 68% for those with four, and up to 90% for patients with eight siblings [*].
One of the key benefits of cord blood stem cell transplants is that the HLAs do not need to be as closely matched as with bone marrow, which needs to be an exact match. Doctors will search public banks if a private source is not available, but it is much harder to find a suitable match in public banks for people of mixed race or ethnicity [*].
2. Conditioning Therapy
Once the appropriate stem cells have been located, the patient will receive high-dose chemotherapy and/or radiation to kill as many cancer cells as possible. They may also get total body irradiation (TBI) to suppress their immune system so it can better tolerate the donor stem cells if there isn’t a perfect HLA match between patient and donor. This process is referred to as conditioning therapy.
3. Transplant Procedure
The transplant will take place 1-3 days after the conditioning therapy has ended. The cord blood units are thawed, tested to ensure they are viable, and infused intravenously into the patient’s blood supply. Because the amount of cord blood stem cells is relative to the patient’s body weight, adult patients may receive stem cells that have been expanded in a lab, or require a second cord blood unit from another cord [*].
The patient is in a delicate position after transplant, with no immune system to take on infection. That's why it’s so important to get the engrafted cells to start doing their job quickly.
Drugs are used to encourage the stem cells to engraft and multiply when they migrate to the bone marrow and begin generating new, healthy blood cells. Different cancer treatment centers have different regimens; Some of the most promising research in stem cell therapy focuses on how to get the stem cells to multiply and engraft more quickly. The FDA recently approved Omidubicel for this purpose [*].
The engrafted cells will begin to form a new immune system that may attack any remaining cancer cells. During this time, patients need to be kept in a sterile room and may also need infusions of red blood cells or platelets while the engraftment progresses.
Doctors typically quantify recovery by the time and number of neutrophils (white blood cells that fight infection) the patient is producing following the transplant. It can take as long as 4-6 weeks to get to a point where the neutrophils can reach a level where they can begin to protect the patient, and 6 months to a year to get to a normal state and activity level [*].
5. Mini-Transplant or Reduced-Intensity Allogeneic Transplant
For older patients and others that cannot tolerate a high dose of chemotherapy, doctors may perform a non-myeloablative transplant (aka mini-transplant). In this novel therapy, patients get lower doses of conditioning therapy that don’t completely destroy their own bone marrow cells before they receive stem cells from an allogeneic donor. The donor’s cells establish a new immune system that sees the leukemia cells as foreign and attacks them, dubbed the graft-vs-leukemia-effect. This effect is not possible in autologous transplants.
Certain patients may be able to have a mini-transplant as an outpatient but it is still considered an experimental procedure at this time for acute myeloid leukemia [*].
Complications of Stem Cell Transplants
The main complications of stem cell transplants, regardless of the source of the stem cells, are infections and graft-vs-host disease (GVHD), when the engrafted cells attack the patient’s healthy cells as invaders. This disease has several levels of severity; It can be chronic and life-threatening.
Symptoms of GVHD can include itching, severe rashes, mouth sores, nausea, severe diarrhea and damage to the liver and lungs, along with fatigue and muscle aches.
Children who have cord blood transplants from a matched sibling have a less than 10% chance of developing GVHD, which is far less than when using bone marrow from the same donor [*].
Cord Blood vs. Bone Marrow: Which Is Better?
Cord blood stem cells offer certain advantages in transplants versus stem cells from bone marrow and peripheral blood sources:
Cord blood stem cells are immunologically naive, meaning they haven’t been exposed to the myriad of infections that cells from adult sources like bone marrow and peripheral blood have been exposed to. This makes these cells less likely to cause graft-vs-host disease (GVHD) [*].
Cord blood stem cells do not need to be as closely HLA-matched as bone marrow and peripheral blood stem cells so it may be easier to find a suitable match.
Outcomes are better for patients that have minimal residual disease (MRD) — where the conditioning therapy performed before the transplant did not destroy all the cancer cells. In patients with MRD who had bone marrow or peripheral blood cells for transplant, only about 33% are still alive 3 years after the transplant, compared to 75% who did not have MRD [*]. Patients with MRD who had cord blood stem cell transplants have much better survival rates [*].
Cord blood stem cells can help prevent the patient’s cancer from returning after treatment [*]. A recent study found that the probability of relapse after cord blood transplant to be lower compared to stem cell transplants from both HLA-matched and HLA-mismatched unrelated donors (both derived from bone marrow or peripheral blood) [*].
Regenerative properties are greater in cord blood. Even though cord blood has fewer stem cells available than bone marrow, the stem cells in cord blood can grow more blood cells than those collected from bone marrow [*].
Cord blood stem cells are available more quickly, and the timing of the transplant can be a critical determinant in its success [*].
Novel Therapies for Leukemia That May Use Cord Blood
Stem cell transplant therapies to treat blood cancers have come a long way since the 1950s and continue to move forward. Here are a few of the most promising clinical trials:
One of the key drawbacks to cord blood stem cells is the low number of cells available in a unit. Omidubicel (marketed by Gamida Cell Ltd. as Omisirge®) is a cord blood expansion therapy that expands the number of cells in the cord blood unit while speeding time to neutrophil engraftment from 22 days down to 12 days [*]. Trials have demonstrated reduced infections and less time in hospital compared to cord blood transplant alone. Omidubicel is the first and only modified allogeneic cord blood-based stem cell transplant to receive “Breakthrough Therapy” designation from the FDA [*].
A clinical trial from Fred Hutch Cancer Center has shown success in using cord blood stem cell transplant to cure HIV in patients with both leukemia and HIV [*].
A clinical trial from CRISPR and Vertex began in 2019 that uses the patient’s own genetically modified stem cells to cure them of the blood disorders sickle cell anemia and beta thalassemia [*]. Snipping a piece of DNA in the bone marrow stem cells frees a blocked gene to make a form of hemoglobin ordinarily only produced by a fetus, which then produces healthy hemoglobin. All 31 patients who had severe sickle cell anemia were cured, and 42 of the 44 patients with beta thalassemia were able to discontinue their drug regimens for the disease. The treatment, known as exa-cel, is likely to be approved for clinical use by the FDA in early December 2023.
While these trials used bone marrow stem cells, what’s important to note is that these genetic blood disorders (like leukemia [*]) would not ordinarily be treatable with the patient’s own stem cells. CRISPR gene editing technology could dramatically change the statistics on autologous vs. allogeneic stem cell transplants in the future and potentially eliminate GVHD as a result.
On the Cutting Edge
MiracleCord offers families the latest technologies in cord blood banking, coupled with affordable pricing and white glove service. That’s why Global Health and Pharma rated us the Best U.S. Cord Blood Bank.
The Bottom Line
The life-saving applications for cord blood and cord tissue continue to grow.
Saving cord blood for all your children could offer them a second chance down the road should they face one of the 80 diseases currently treated with cord blood stem cell transplant therapy, not to mention treatments to come.
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