How Stem Cells Are Harvested for Bone Marrow Transplants: A Comprehensive Guide

When it comes to treating life-threatening blood disorders and certain cancers, bone marrow transplantation—more accurately referred to as hematopoietic stem cell transplantation (HSCT)—plays a crucial role. Despite the name, most modern procedures do not involve extracting stem cells directly from the bone marrow. Instead, the majority of transplants today rely on peripheral blood stem cells, with only specific cases requiring traditional bone marrow harvests.

Understanding Hematopoietic Stem Cell Sources

There are two primary sources for harvesting stem cells used in transplantation: peripheral blood stem cells (PBSC) and bone marrow-derived stem cells. Both methods aim to collect healthy, functioning stem cells that can regenerate a patient's blood and immune system after high-dose chemotherapy or radiation.

Peripheral Blood Stem Cell Collection (Most Common Method)

In recent years, peripheral blood has become the preferred source for stem cell donation in most countries, including China. This method involves collecting stem cells from the donor's bloodstream rather than the bone itself. Donors typically undergo a five-day regimen of growth factor injections (like G-CSF) to stimulate the release of stem cells from the bone marrow into the circulating blood.

The actual collection process is similar to donating platelets. Blood is drawn from one arm, passed through an apheresis machine that separates out the stem cells, and then returned to the body through the other arm. The procedure is outpatient, generally takes 4–6 hours, and is minimally invasive with mild side effects such as bone aches or fatigue.

Bone Marrow Harvesting (Used in Specific Cases)

While less common today, direct bone marrow extraction is still necessary for certain conditions such as severe aplastic anemia or pediatric cases where bone marrow grafts offer better engraftment outcomes. In these instances, stem cells are collected from the posterior iliac crest—the back of the pelvic bone—using a special needle under general or regional anesthesia.

This surgical procedure involves multiple punctures to aspirate red bone marrow rich in stem cells. Although more invasive, it poses minimal long-term risks, and donors usually recover within a few days to a week. The harvested marrow is then processed and infused into the recipient to rebuild their blood-forming system.

Why the Shift Toward Peripheral Blood?

Medical advancements have made peripheral blood stem cell transplantation faster, more efficient, and easier for donors. It allows for quicker recovery times and higher stem cell yields. However, doctors carefully evaluate each case to determine whether PBSC or traditional marrow harvest offers the best outcome for the patient.

Ultimately, both methods save lives. Whether through blood or bone, the generosity of donors enables patients battling leukemia, lymphoma, and other hematologic diseases to receive a second chance at life.