Hematopoietic stem and progenitor cells (HSPCs) are special cells that serve as the origin for all types of blood cells within the body. These cells continuously produce billions of new blood cells daily, ensuring a healthy blood supply. Their ability to generate diverse specialized cells makes them a foundation for various medical treatments.
What are Hematopoietic Stem and Progenitor Cells?
HSPCs possess unique biological characteristics that enable their role in blood cell production. One property is self-renewal, meaning they can divide to create more HSPCs, maintaining a consistent pool of these foundational cells throughout a person’s life. This ensures a continuous supply of cells needed for blood formation.
Beyond self-renewal, HSPCs are multipotent, meaning they can differentiate into various specialized blood cell types. This allows a single HSPC to give rise to all the different components of blood, from oxygen carriers to immune defenders. Hematopoietic stem cells are more primitive, possessing an indefinite capacity for self-replication and the ability to differentiate into a wider range of cell types, including both myeloid and lymphoid progenitors. Progenitor cells, which develop from stem cells, are more committed to specific cell lineages and have a more restricted differentiation potential. While some progenitor cells may be multipotent, they have a lesser ability to self-renew compared to stem cells, making their self-replication limited.
Sources of Hematopoietic Stem and Progenitor Cells
HSPCs are found in several locations within the body, which also serve as sources for medical collection. The primary natural source in adults is the bone marrow, the spongy tissue found inside bones. Bone marrow cells are collected through a surgical procedure where hollow needles remove marrow from hip bones.
Another rich source of HSPCs is umbilical cord blood, collected at birth from the umbilical cord and placenta. This source has advantages, such as potentially requiring less precise tissue matching and a decreased incidence of graft-versus-host disease. HSPCs can also be obtained from peripheral blood, the blood circulating throughout the body. To increase the number of HSPCs in peripheral blood for collection, mobilizing agents like granulocyte colony-stimulating factor (G-CSF) are administered, which prompt the cells to move from the bone marrow into the bloodstream where they can be collected via apheresis.
The Process of Blood Cell Formation
The continuous and regulated process by which HSPCs give rise to all types of blood cells is known as hematopoiesis. This system ensures the body constantly produces new blood cells to replace old or damaged ones.
During hematopoiesis, HSPCs differentiate into major blood cell lineages, each with distinct functions.
Red Blood Cells
Red blood cells (erythrocytes) transport oxygen from the lungs to tissues and return carbon dioxide. These cells contain hemoglobin, an iron-rich protein that binds to oxygen.
White Blood Cells
White blood cells (leukocytes) are a diverse group of cells that form a core part of the body’s immune system, defending against infections and diseases. Major types include neutrophils, lymphocytes, and monocytes.
Platelets
Platelets (thrombocytes) are small cell fragments that are essential for blood clotting, helping to stop bleeding by forming a plug at injury sites.
The entire process of blood cell formation is tightly controlled by various growth factors and transcription factors to ensure appropriate cell counts and overall blood homeostasis.
Medical Applications of Hematopoietic Stem and Progenitor Cells
The unique properties of HSPCs have led to their widespread use in various medical applications. Hematopoietic Stem Cell Transplantation (HSCT), also known as bone marrow transplantation, is a well-established treatment for several conditions, particularly blood cancers such as leukemia, lymphoma, and multiple myeloma. In HSCT, damaged bone marrow is replaced with healthy HSPCs, which then regenerate the patient’s blood-forming system. This procedure is also used for other blood disorders like aplastic anemia and sickle cell disease, where it helps to replace dysfunctional cells with healthy ones.
Beyond transplantation, HSPCs are being explored in gene therapy, an emerging field where these cells are genetically modified to treat inherited disorders. For example, HSPCs can be collected from a patient, corrected genetically in a laboratory, and then reinfused to deliver therapeutic genes, potentially treating conditions like primary immunodeficiencies and beta-thalassemia. Researchers also utilize HSPCs in laboratory settings to deepen their understanding of disease mechanisms and to develop new therapeutic strategies.