Stem cells play an integral role in the development and function of biological systems. They are cells that can replicate and differentiate into multiple cell types with numerous functions. Depending on their differentiation potential, stem cells are divided into five categories: totipotent, pluripotent, multipotent, oligopotent and unipotent (Figure 1). Totipotent stem cells are cells that can differentiate into any cell type within the body. The human zygote is a good example of a totipotent stem cell as it has the ability to differentiate into all cell types that make up the human adult and the placenta 1. Pluripotent stem cells are cells that can differentiate into all three germ layers: ectoderm, mesoderm, and endoderm. Examples include induced pluripotent stem cells and embryonic stem cells1,2. Multipotent stem cells, on the other hand, can only differentiate into limited cell types. Mesenchymal stem cells which can differentiate into cells of mesenchymal stromal origin (osteocytes, chondrocytes, and adipocytes) or hematopoietic stem cells which can differentiate into cells of myeloid and lymphoid lineages are examples of multipotent stem cells1,3. Oligopotent stem cells can differentiate into only a few cell types. Examples of oligopotent stem cells include myeloid progenitor cells, lymphoid progenitor cells, and intestinal stem cells3. Unipotent stem cells, such as epidermal cells, magakaryocytes, or Type II pneumocytes in the lung, are cells that can replicate and replace senescent cells but can only differentiate into a single cell type1,3.