A peripheral blood stem cell (PBSC) transplant is a medical procedure that replaces damaged or destroyed blood-forming stem cells. This treatment is used when conditions like leukemia, lymphoma, multiple myeloma, or high-dose cancer therapies such as chemotherapy or radiation have compromised a patient’s ability to produce healthy blood cells. The transplant introduces healthy stem cells to restore this vital function.
Understanding Peripheral Blood Stem Cell Transplants
Peripheral blood stem cells are immature blood-forming cells found mainly in the bone marrow, but also circulating in the bloodstream. These cells generate all blood cell types, including white blood cells for infection fighting, red blood cells for oxygen transport, and platelets for clotting.
PBSC transplants are categorized by the stem cell source. An autologous PBSC transplant uses the patient’s own stem cells, collected and stored before high-dose chemotherapy or radiation. This method is used for certain cancers that respond well to chemotherapy, such as multiple myeloma or lymphoma, to reduce relapse risk and extend survival.
An allogeneic PBSC transplant uses stem cells from a donor, who may be a matched family member or an unrelated individual from a registry. These transplants are for cancers less responsive to chemotherapy or for non-cancerous blood diseases like aplastic anemia. A benefit of allogeneic transplants is the “graft-versus-tumor” effect, where donor immune cells can help eliminate remaining cancer cells.
The PBSC Transplant Process
The PBSC transplant process begins with stem cell collection. For both autologous and allogeneic transplants, stem cells are mobilized from the bone marrow into the bloodstream using medications, such as granulocyte colony-stimulating factor (G-CSF), to increase the number of stem cells circulating in the peripheral blood.
Once enough stem cells are circulating, they are collected through apheresis. This outpatient procedure draws blood from one arm, separates and collects the stem cells using a machine, and returns the remaining blood components to the other arm. Apheresis sessions typically last four to six hours and may be repeated over one to three days.
After collection, the recipient undergoes a “conditioning” regimen of high-dose chemotherapy, sometimes with radiation therapy, over several days. This phase eliminates diseased cells, especially cancer cells, and suppresses the recipient’s immune system to prevent rejection of the transplanted cells. The conditioning regimen is tailored to the patient’s disease and health.
The transplant occurs after conditioning. The collected stem cells are infused into the recipient’s bloodstream through a central venous catheter, similar to a blood transfusion. These healthy stem cells then migrate to the bone marrow, a process called “homing,” where they engraft. Engraftment means they settle, multiply, and begin producing new, healthy blood cells.
Recovery and Post-Transplant Considerations
Following a PBSC infusion, recovery focuses on the engraftment of new stem cells, which typically occurs within the first 30 days. During this time, the transplant team closely monitors blood counts, including white blood cells, neutrophils, red blood cells, and platelets, to confirm new cell production. Neutrophil engraftment can occur as early as 12 days post-infusion.
Patients face increased infection susceptibility during initial recovery due to a weakened immune system from conditioning therapy. Low white blood cell counts, especially neutrophils, leave patients vulnerable to bacterial, viral, and fungal infections until engraftment is complete. Monitoring and preventative measures are crucial to manage these risks.
Complications can arise short-term and long-term. In allogeneic transplants, graft-versus-host disease (GVHD) is a concern, occurring when donor immune cells attack recipient cells. Acute GVHD typically develops within three months, with symptoms like skin rash, liver dysfunction, or gastrointestinal issues. Chronic GVHD can develop later, affecting various organs. While serious, a mild form of GVHD may indicate a beneficial anti-cancer effect.
Other complications include conditioning regimen side effects like nausea, vomiting, mouth sores, or fatigue. Long-term follow-up care involves regular monitoring, adherence to medications like immunosuppressants, and lifestyle adjustments such as dietary precautions and avoiding infection exposure.
PBSC vs. Bone Marrow Transplants
Peripheral blood stem cell transplants and traditional bone marrow transplants both replace damaged blood-forming cells, but they differ in collection method and patient outcomes. PBSC collection is a non-surgical apheresis process, while bone marrow collection involves a surgical procedure to harvest stem cells directly from the bone marrow, typically from the hip bone.
Donor recovery time is generally faster for PBSC donation, about one week, compared to approximately 2.3 weeks for bone marrow donors, who may experience skeletal pain or fatigue. For recipients, PBSC transplants lead to faster engraftment of both neutrophils and platelets compared to bone marrow transplants.
While PBSC transplants offer quicker engraftment, they may have a higher incidence of chronic graft-versus-host disease (GVHD) compared to bone marrow transplants. However, for certain advanced hematologic malignancies, PBSC transplants can offer a survival advantage by reducing relapse rates. The choice between PBSC and bone marrow transplantation depends on factors like the patient’s disease, overall health, and donor availability, with doctors weighing faster engraftment against GVHD risk.