**2. Stem cells**

The term stem cell stands for the population of immature precursor cells, which are able to renew themselves and be the source of de novo replacement for many body tissues. Stem cells are classified into two main groups: embryonic stem cells (ESCs) and adult stem cells. ESCs can be obtained from the inner cell mass of the embryonal blastocyst. Although they are easily achieved, some disadvantages restrict their application. Adult stem cells such as mesenchymal and haematopoietic stem cells (HSCs) are obtained from mature tissues. Due to their plasticity, adult stem cells produce cell lineage different from their original organ. Thus, adult stem cells seem to be an appropriate candidate for organ regeneration in different kinds of diseases or lost/damaged organs. **Table 1** represents the main stem cell and their advantages and disadvantages.


**Table 1.** Main stem cell and their advantages and disadvantages.
