Stem cells are among the most fascinating cells in the human body. They can renew themselves over and over again, and can differentiate into specialized cells. Given their unique regenerative abilities, they offer great potential for treating a wide range of diseases. Cell culture studies play a crucial role in enabling scientist to better understand stem cells’ properties, their behavior after transplantation, as well as their interactions with the microenvironment.
Many different types of stem cell come from various areas of the body, or are formed at different times in our lives. Embryonic stem cells exist only at the earliest stages of development, whereas various types of adult stem cells are found in almost all tissues and organs, and play a crucial role in homeostasis and repairing processes.
Among adult stem cells, hematopoietic stem cells (HSC) hold great potential for further applications in regenerative medicine. They are primarily found in the bone marrow of adults, where they can give rise to all types of blood cells. HSCs have been used for more than 40 years in the therapy of hematological malignancies (Sieburg et al., 2005; Thomas et al., 1957). Although not considered a classical adult stem cell, monocytes can acquire stem cell-like properties, as they can differentiate into diverse cell types, including dendritic cells, macrophages, and osteoclasts (Ungefroren et al., 2016).
Pericytes are multipotent mesenchymal-like cells embedded in the basement membrane of capillaries and venules. They are central to angiogenesis, and are important for structural integrity of the microvasculature, as well as for blood flow regulation (Ribatti et al., 2011). It is now also possible to reprogram tissue-specific cells so they become embryonic stem cells. These induced pluripotent stem cells (iPSCs) help scientists learn more about physiological and pathological processes. Such iPSCs are also useful for generating patient-specific disease models and for testing new drugs and therapies (Yu et al., 2007; Kumar et al., 2017).
Cell therapy represents a very promising approach in many clinical fields, and numerous clinical trials with stem cells are currently in progress. Among the stem cells, mesenchymal stem cells (MSC) provide powerful therapeutic tools, as they can modulate immune responses, and promote wound healing and tissue regeneration. In addition, they are free of ethical concerns, can be harvested from various sites and show low immunogenicity (Ballini et al., 2017; Wei et al., 2013).
MSCs can be used for treating several immune-mediated diseases such as the graft-versus-host disease (GvHD) following bone marrow transplantation (Amorin et al., 2014), systemic lupus erythematosus (Cras et al., 2015), Chron’s disease and multiple sclerosis (Miguel et al., 2012). Potential applications in regenerative medicine include regenerating bone (Arthur et al., 2009), developing insulin-producing cells for type 1 diabetes (Wu et al., 2014), repairing damaged heart muscle following a heart attack (Gersh et al., 2009), and improving the liver function in patients with cirrhosis (Kharaziha et al., 2009).
Scientists can also use stem cells, or tissues grown from them, to develop new drugs, and to test how novel compounds might affect various organs, or how effective such compounds are on different individuals (Liu et al., 2013). Stem cell research is essential for delivering insights that allow scientists to characterize the factors regulating stem cell proliferation and self-renewal, as well as the biological processes and molecular mechanism of stem cell differentiation. Studies of human embryonic stem cells are focusing on identifying how undifferentiated stem cells become the differentiated cells that form tissues and organs.
Some of the most serious medical conditions, such as cancer and birth defects, arise from abnormal cell division and differentiation, so a better understanding of the inner working of living organisms could lead to earlier detection, better diagnosis and more effective treatments for diseases.
Further studies on adult stem cells are needed to answer many important questions about their development and ability to home in to sites of injury. Scientists are also exploring how to use stem cells to generate tissue that could replace tissue that has been damaged by disease, aging or injury (Nelson et al., 2009). This is particularly relevant considering the lack of organs available for transplantation compared to the growing needs for an ageing population. Whole-organ engineering of livers, kidneys, hearts, or lungs is particularly challenging because of the structural complexity and heterogeneity of the cells that make up these organs (Stoltz et al., 2015).