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Mobilization Mechanics: The Complex World of Stem Cell Mobilization

Jul 24, 2019 10:11:00 AM / by Nancy Andon, MSc

Brad_donation4-brighter (002)-1Stem cells are the foundation from which all other cells with specialized functions are generated. Stem cells are primarily found in the bone marrow, where they are produced, but can be induced to migrate into the peripheral blood circulation through a process known as mobilization.

Mobilization involves the recruitment of stem and progenitor cells from the bone marrow into the bloodstream, through the administration of various cytokines and growth factors. The discovery that mobilized peripheral blood could successfully be used as a stem cell source in the clinic eventually led to the preferential use of mobilized blood products for research and process development. The availability and ease of collection of stem cells from the peripheral blood of donors is a major advantage as developing therapies progress through the development continuum.

While mobilization of stem cells is easier and relatively painless compared to collection of stem cells from the bone marrow, it is nevertheless an intricate procedure. The whole process must be managed with expertise by industry professionals such as clinical recruitment specialists, qualified apheresis nurses, and medical directors.

Donor Recruitment and Selection Process

Donors are at the heart of the mobilization process. During the course of donor screening and selection, many factors have to be considered. Age, weight, gender, ethnicity, HLA-typing, medical history, and other demographic criteria should all be matched as closely as possible to the client’s study design and their intended use for the isolated stem cells. It is recommended that back-up donors are also recruited and screened for each client, in case the primary donor defers or must withdraw from the process due to medical reasons.

In addition to the initial identification and recruitment efforts, selected donors who present to the apheresis collection center answer a health questionnaire and undergo a vitals check. Donors are rigorously screened in order to avoid infectious disease transmission and to ensure that their current health is robust enough to complete the donation procedure. Moreover, urinalysis and blood screening samples are collected and a physical exam is completed. Once an optimal matching donor is found, cell collection centers must ensure that the donor is fully informed about what the process involves and what risk they may be exposed to before giving their consent to donate.

Recruitment is a time-consuming process, not every apheresis donor is willing or even physically able to participate in the mobilization program. Since potential donors do fail screening or decide to drop out of the process, successful mobilized blood collection relies on access to a large, diverse donor network.


Once a donor agrees to participate in the mobilized donor program, they will once again undergo a medical exam, including a blood draw for a complete blood count (CBC) and metabolic panel. Donors are assigned to the project for which they are best suited, based on client requirements. These requirements are developed in accordance with research or process development parameters, as well as prior experimental findings.  

Mobilization agents that are used to stimulate the movement of stem cells into the peripheral blood circulation can vary according to need. The most commonly used agents are:

  • Neupogen® (G-CSF) – an extremely well-characterized growth factor that stimulates the bone marrow to produce stem cells and release them into the blood
  • Mozobil® – a mobilizing agent, often used in combination with G-CSF to try to optimize stem cell release

The exact combination of mobilizing agents used to produce a particular mobilized blood product is selected by the customer based on their study criteria. Mobilizing agents can sometimes cause mild side effects, and therefore donors must be monitored closely throughout the dosing schedule to ensure their safety and comfort with the procedure.

Cell Collection

Cell collection is carried out via apheresis, a process by which blood is collected from the donor and separated into its various components using a specialized instrument. The stem-cell containing fraction of blood is diverted into a collection bag, while the other blood components are returned to the donor. The whole process takes several hours; on occasion, customers may request two successive collection sessions following mobilization if they judge that this will be needed to meet project requirements.

HemaCare’s third-party institutional review board (IRB), approved a lifetime maximum of two mobilized stem cell donations from the same donor to ensure the safety and wellbeing of our donors. Mobilized blood products may be freshly isolated and processed within 48 hours, or frozen and stored for future use.

Planning for the Future

Mobilized blood products are keenly needed in order for the research industry to meet increased demand for regenerative therapies. Mobilized peripheral blood collection via apheresis provides for improved availability of stem cells and is now the main source of stem cells collected from healthy donors. It reliably produces high stem cell yields, is simpler to perform, and is associated with fewer donation-related side effects. However, while stem cell mobilization is considered easier than bone marrow donation on the donor, it’s important to realize that producing mobilized stem cells is a complicated process that must be managed continuously to achieve the best results.

At HemaCare, donor safety and consistently high-quality products are our top priorities.

To view our infographic on what goes into producing our selection of mobilized blood products, click here.

Topics: Apheresis, Stem Cells

Nancy Andon, MSc

Written by Nancy Andon, MSc

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