Stem cells are often referred to as the body’s master cells because they possess the unique capacity to both renew themselves and specialize into many other cell types. This ability allows them to serve as a repair system, replenishing specialized cells throughout a person’s life. While these biological units are most commonly associated with bone marrow, functional stem cells can indeed be obtained from peripheral blood. Although the number of these cells naturally found in the bloodstream is low, modern medical techniques make it possible to collect them in therapeutic quantities for medical procedures.
The Specific Stem Cells Found in Blood
The specialized stem cells collected from the circulating blood are known as Hematopoietic Stem Cells (HSCs). These are the essential building blocks of the entire blood and immune system. The primary function of an HSC is to generate all mature blood cell types, a process called hematopoiesis. This includes producing red blood cells, platelets for clotting, and the various white blood cells that make up the immune defense system.
HSCs primarily reside within the bone marrow, the soft, spongy tissue inside certain bones. A small population naturally circulates in the peripheral blood, allowing for routine surveillance and movement to sites of injury or need.
The focus on HSCs distinguishes this therapeutic approach from others that utilize embryonic or induced pluripotent stem cells, which can become almost any cell type. The multipotent nature of HSCs makes them perfectly suited for restoring a damaged blood system.
Increasing Cell Count and Collection Methods
Because the concentration of hematopoietic stem cells in the peripheral blood is naturally low, a process called “mobilization” is required to increase their numbers before collection can occur. This involves administering a growth factor known as Granulocyte Colony-Stimulating Factor (G-CSF). G-CSF is a naturally occurring protein that stimulates the bone marrow to dramatically increase its production of white blood cells and release a large number of HSCs into the bloodstream.
This medication is typically given via a subcutaneous injection for four to five days, causing the stem cell count in the blood to rise significantly. The collection itself is performed through a non-surgical, outpatient procedure known as apheresis. The process involves drawing blood from a vein and passing it through a specialized machine called a cell separator.
The apheresis machine uses centrifugal force to spin the blood and separate it into its component parts based on density. The machine identifies and extracts the layer containing the stem cells, while the remaining components are returned to the donor’s body. A single apheresis session typically lasts between three and five hours, and multiple sessions may be needed to collect the required number of cells for transplantation.
Therapeutic Applications of Blood Stem Cells
Once collected, the hematopoietic stem cells are used in a blood stem cell transplant, which is a standard treatment for numerous diseases. This therapy is primarily used to treat certain cancers, such as leukemia, lymphoma, and multiple myeloma, as well as non-malignant blood disorders like aplastic anemia and sickle cell disease. The ultimate purpose of the transplant is to replace a patient’s unhealthy or destroyed blood-forming system with a new, healthy one.
The procedure is often necessary after a patient has undergone high-dose chemotherapy or radiation, which eliminates cancerous cells but also destroys the healthy stem cells in the bone marrow. The infused stem cells then travel to the bone marrow cavity and begin the process of engraftment, establishing a new, fully functional blood and immune system.
Transplants are categorized based on the cell source: autologous transplants use the patient’s own collected cells, while allogeneic transplants use cells from a healthy donor. Peripheral blood collection has largely become the preferred method over traditional bone marrow aspiration because it is a less invasive procedure for the donor, resulting in a faster and easier recovery. This accessibility has made the peripheral blood source a primary option for donors worldwide.