A stem cell is characterized by two primary abilities: self-renewal and differentiation. Self-renewal means the cell can divide to produce more copies of itself. Differentiation is the process where a stem cell transforms into a specialized cell, such as a neuron or heart cell. Scientists use the term “potency” to describe the full range of specialized cells a stem cell can generate. The distinction between various levels of potency is significant in biology and medicine, especially when comparing pluripotent and multipotent cells. This article clarifies the differences in capability and application between these two categories.
Defining the Stem Cell Potency Spectrum
Potency represents a hierarchy of developmental potential. The most capable cells are considered totipotent, which can form every cell type in the body, including extraembryonic tissues like the placenta. At the opposite end are unipotent cells, which are the most restricted and can only differentiate into a single cell type, such as muscle stem cells.
Pluripotent and multipotent cells fall between these extremes. Understanding this hierarchy places the power of these cells into context regarding their developmental origins and therapeutic applications. The greater a cell’s potency, the greater its capacity to differentiate, but also the greater the complexity in controlling its final fate.
Pluripotent Cells and Their Capabilities
Pluripotent stem cells possess the ability to differentiate into cells derived from all three primary germ layers: the endoderm, mesoderm, and ectoderm. These three layers are formed during early embryonic development and collectively give rise to every tissue and organ in the adult body. Pluripotent cells can form all body cell types, but they cannot form the placenta or other extraembryonic structures, distinguishing them from totipotent cells.
Germ Layer Derivatives
The ectoderm forms outer structures like the skin epidermis, the nervous system, and sensory organs. The endoderm develops into the inner linings of the digestive and respiratory systems, along with organs like the liver and pancreas. The mesoderm gives rise to the musculoskeletal system, including bone and muscle, the circulatory system, and connective tissues.
The most well-known examples are Embryonic Stem Cells (ESCs), derived from the inner cell mass of the blastocyst. Scientists can also create Induced Pluripotent Stem Cells (iPSCs) by genetically reprogramming adult somatic cells, such as skin cells, back into an ESC-like state. Both ESCs and iPSCs share the characteristic of being able to differentiate into any cell derived from the three germ layers.
Multipotent Cells and Their Restricted Lineage
Multipotent stem cells have a restricted developmental potential. These cells differentiate into a number of cell types, but only within a specific, closely related family or lineage. They are often referred to as adult stem cells because they reside in specific tissues throughout the body, functioning to maintain and repair their tissue of origin.
A classic example is the Hematopoietic Stem Cell (HSC), found in the bone marrow. HSCs differentiate only into all types of blood cells, including red blood cells, white blood cells, and platelets. Similarly, Mesenchymal Stem Cells (MSCs), found in bone marrow and adipose tissue, can differentiate into bone cells (osteoblasts), cartilage cells (chondrocytes), and fat cells (adipocytes), all mesodermal derivatives.
The fundamental difference is their developmental ceiling: a multipotent cell is committed to a specific germ layer or sub-lineage, while a pluripotent cell retains the potential to enter any of the three germ layer pathways. This lineage restriction makes multipotent cells specialized for tissue-specific repair and regeneration.
Practical Applications of the Distinction
The difference in potency affects how these cells are sourced and used in medicine. Multipotent cells are sourced from adult tissues, like bone marrow or fat, making their collection less ethically complex than obtaining human ESCs. Since multipotent cells are restricted to a tissue lineage, they are used in therapies targeting specific, localized repair, such as bone marrow transplants utilizing HSCs to restore blood cell production.
Pluripotent cells, due to their ability to form any cell type, are the focus for large-scale cell replacement therapies and disease modeling. Researchers can direct iPSCs to become new pancreatic beta cells to treat diabetes or new neurons to study neurological disorders. Using iPSCs derived from a patient’s own cells helps avoid immune rejection during transplantation.
The higher potency of pluripotent cells introduces a challenge: uncontrolled differentiation can lead to tumors called teratomas if not properly managed. The restricted behavior of multipotent cells often makes them a safer and more direct option for therapies targeting their native tissues. Therefore, the choice of cell type depends on the therapeutic goal, balancing the broad potential of pluripotent cells against the specialized function of multipotent cells.