What are progenitor cells?
Every cell in the human body, and that of other mammals, originates from stem cell precursors. Progenitor cells are descendants of stem cells that then further differentiate to create specialized cell types.
There are many types of progenitor cells throughout the human body. Each progenitor cell is only capable of differentiating into cells that belong to the same tissue or organ. Some progenitor cells have one final target cell that they differentiate to, while others have the potential to terminate in more than one cell type.
Progenitor cells vs. stem cells
Stem cells share two qualifying characteristics. Firstly, all stem cells have the potential to differentiate into multiple types of cells. Secondly, stem cells are capable of unlimited self-replication via asymmetric cell division, a process known as self-renewal.
There are two broad categories of stem cells found in all mammals. The first are embryonic stem cells. These cells arise from the inner cell mass of the blastocyst in an early-stage embryo. Embryonic stem cells are the blueprint used to create every cell in the body. Because they can be used to create any type of cell, they are known as pluripotent.
The second type of stem cells found in mammals are adult stem cells (or somatic stem cells). Unlike pluripotent embryonic stem cells, adult stem cells are more limited in relation to the type of cells that they become. Unlike embryonic stem cells that could be used to create any cell, adult stem cells are limited to generating cell types within a specific lineage, such as blood cells or cells of the central nervous system. This level of differentiation potential is termed multipotent.
Stem cells create two types of progeny: more stem cells or progenitor cells. All progenitor cells are descendants of stem cells. When it comes to cell differentiation, they fall on the spectrum between stem cells and fully differentiated (mature) cells.
Whilst stem cells have indefinite replication (left) progenitor cells can at most differentiate into multiple types of specialized cell (right).
Properties of progenitor cells
Cellular repair or maintenance
Multipotent, oligopotent, or unipotent
Further differentiated cells (either progenitor cells of mature/fully differentiated cells)
Types of progenitor cells
Progenitor cells are an intermediary step involved in the creation of mature cells in human tissues and organs, the blood, and the central nervous system.
Neural progenitor cells
The human central nervous system (CNS) contains three types of fully differentiated cells: neurons, astrocytes and oligodendrocytes. The latter two are collectively known as glial cells.
Every neuron, oligodendrocyte and astrocyte in the CNS evolves from the differentiation of neural progenitor cells (NPCs). NPCs themselves are produced by multipotent neural stem cells (NSCs). Both NPCs and NSCs are termed neural precursor cells.
Before the 1990s, it was believed that neurogenesis terminated early in life. More recent studies demonstrate that the brain contains stem cells that are capable of regenerating neurons and glial cells throughout the human lifecycle. These stem cells have only been found in certain brain regions, including the striatum and lateral ventricle.
Hematopoietic progenitor cells
Hematopoietic progenitor cells (HPCs) are an intermediate cell type in blood cell development. HPCs are immature cells that develop from hematopoietic stem cells, cells that can both self-renew and differentiate into hematopoietic progenitor cells. HPCs eventually differentiate into one of more than ten different types of mature blood cells.
Hematopoietic progenitor cells are categorized based upon their cell potency, or their differentiation potential. As blood cells develop, their potency decreases.
First, hematopoietic stem cells differentiate into multipotent progenitor cells. Multipotent progenitor cells are those with the potential to differentiate into a subset of cell types. These cells then differentiate into either the common myeloid progenitor (CMP) or common lymphoid progenitor (CLP). Both CMPs and CLPs are types of oligopotent progenitor cells (progenitor cells that differentiate into only a few cell types).
CMPs and CLPs continue to differentiate along cell lines into lineage-restricted progenitor cells that become final, mature blood cells.
Myeloid progenitor cells are precursors to the following types of blood cells:
- Red blood cells/erythrocytes
- Mast cells
- Dendritic cells
Lymphoid progenitor cells (also known as lymphoblasts) are precursors to other mature blood cell types, including:
- NK-cells/Natural killer cells
- Dendritic cells
Function of progenitor cells
The primary role of progenitor cells is to replace dead or damaged cells. In this way, progenitor cells are necessary for repair after injury and as part of ongoing tissue maintenance. Progenitor cells also replenish blood cells and play a role in embryonic development.
Uses of progenitor cells in medicine
Neural progenitor cells (NPCs) are being explored alongside neural stem cells for their potential to treat diseases of or injury to the central nervous system. A deeper understanding of how these cells function on a cellular and molecular basis is needed to progress from early experimental research to therapeutic use.
NPCs are currently utilized in research conducted on CNS disorders, development, cell regeneration and degeneration, neuronal excitability, and therapy screening. When compared to induced pluripotent stem cells, which are cells reprogrammed into a pluripotent state, NPCs can cut down on time in some experiments.
Hematopoietic progenitor cells and stem cells are being researched for their capacity to treat blood cell disorders. They are also currently used to help treat patients with a variety of malignant and non-malignant diseases via bone marrow transplants that deliver bone marrow and peripheral blood progenitor cells to patients. These procedures can assist patients in recovering from the damage caused by chemotherapy.
Additionally, researchers are examining the potential of using progenitor cells to create a variety of tissues, such as blood vessels, heart valves, and electrically conductive tissue for the cardiovascular system.