The two criteria that any given stem cell has to fulfil are:

• The ability of self-renewal to maintain its own population in undifferentiated state
• Potency, the capacity to give rise to differentiated, specialized progeny cells. While self-renewal is pretty much undisputed, the potency of a stem cell can vary greatly which is why this trait is used to classify stem cells.

Pluripotent and multipotent stem cells are the stem cells in the spotlight of research and clinical applications. Totipotent cells are often extremely difficult to obtain and limited in numbers. Additionally, controlling their vast potency poses its own challenges. Oligopotent and unipotent cells, on the other hand, are generally too limited in their applicability due to their restricted potency.

Pluripotent stem cells are undifferentiated, and yet they can give rise to all of the differentiated cells in the body, such as heart muscle cells, blood cells, and nerve cells.  Pluripotent stem cells have the ability to differentiate into all of the cells of the adult body. For example, pluripotent stem cells can differentiate into cardiac cells, neuronal cells or epithelial cells, depending on the cell induction and signalling.

Adult stem cells are found in a tissue or organ and can differentiate to yield the specialized cell types of that tissue or organ. For example, a haemopoietic stem cell derived from bone marrow can differentiate into any of the blood cell lineage. Adult stem cells serve as an internal repair system that generates replacements for cells that are lost through normal wear and tear, injury, or disease throughout the life of the organism. Adult stem cells have been identified in many organs and tissues and are generally associated with specific anatomical locations. These stem cells may remain quiescent (non-dividing) for long periods of time until they are activated by a normal need for more cells to maintain and repair tissues.

In 2006, researchers identified conditions that would allow some mature human adult cells to be reprogrammed into an embryonic stem cell-like state. Those reprogramed stem cells are called induced pluripotent stem cells (iPSCs).

Stem cells have unique abilities to self-renew and to recreate functional tissues.

Stem cells may replicate many times, unlike muscle cells, blood cells, or nerve cells, which do not normally replicate. Different types of stems cells have varying degrees of potency; that is, the number of different cell types that they can form. While differentiating, the cell usually goes through several stages, becoming more specialized at each step. Scientists are beginning to understand the signals that trigger each step of the differentiation process. Signals for cell differentiation include factors secreted by other cells, physical contact with neighbouring cells, and certain molecules in the microenvironment.

Growing cells in the laboratory is known as “cell culture.” Stem cells can proliferate in laboratory environments in a culture dish that contains a nutrient broth known as culture medium (which is optimized for growing different types of stem cells). Most stem cells attach, divide, and spread over the surface of the dish.

The culture dish becomes crowded as the cells divide, so they need to be re-plated in the process of subculturing, which is repeated periodically many times over many months. Each cycle of subculturing is referred to as a “passage.” The original cells can yield millions of stem cells. At any stage in the process, batches of cells can be frozen and shipped to other laboratories for further culture and experimentation.

Differentiated cells, such as skin cells, can be reprogrammed back into a pluripotent state. Reprogramming is achieved over several weeks by forced expression of genes that are known to be master regulators of pluripotency. At the end of this process, these master regulators will remodel the expression of an entire network of genes. Features of differentiated cells will be replaced by those associated with the pluripotent state, essentially reversing the developmental process.

As long as the pluripotent stem cells are grown in culture under appropriate conditions, they can remain undifferentiated. To generate cultures of specific types of differentiated cells, scientists may change the chemical composition of the culture medium, alter the surface of the culture dish, or modify the cells by forcing the expression of specific genes. Through years of experimentation, scientists have established some basic protocols, or “recipes,” for the differentiation of pluripotent stem cells into some specific cell types.

An important potential application is the generation of cells and tissues for cell-based therapies, also called tissue engineering. The current need for transplantable tissues and organs far outweighs the available supply. Stem cells offer the possibility of a renewable source. There is typically a very small number of adult stem cells in each tissue, and once removed from the body, their capacity to divide is limited, making generation of large quantities of adult stem cells for therapies difficult. In contrast, pluripotent stem cells are less limited by starting material and renewal potential.

To realize the promise of stem cell therapies in diseases, scientists must be able to manipulate stem cells so that they possess the necessary characteristics for successful differentiation, transplantation, and engraftment. Scientists must also develop procedures for the administration of stem cell populations, along with the induction of vascularization (supplying blood vessels), for the regeneration and repair of three-dimensional solid tissues.

To be useful for transplant purposes, stem cells must be reproducibly made to:

• Proliferate extensively and generate sufficient quantities of cells for replacing lost or damaged tissues.
• Differentiate into the desired cell type(s).
• Survive in the recipient after transplant.
• Integrate into the surrounding tissue after transplant.
• Avoid rejection by the recipient’s immune system.

Function appropriately for the duration of the recipient’s life.

Stem cells are wonders of the formation and regeneration of life and form the building blocks of multicellular life on Earth. Stem cells have the remarkable potential to renew themselves. They can develop into many different cell types in the body during early life and growth.

Stem cell therapy is a newer treatment that is still being researched. Stem Cell therapy can be categorized into:

• Regenerative Medicine

  • Anti-Aging & Wellness

• Neurodegenerative conditions:

  • Parkinson’s disease

  • Alzheimer’s disease

  • Multiple sclerosis(MS)

  • Amyotrophic lateral sclerosis(ALS)

  • Motor neurone disease (MND)

• Rehabilitative Medicine

  • Post stroke recovery

  • Spinal cord injury

  • Post myocardial infarct

• Cancer

  • Leukaemia

  • Lymphoma

  • Neuroblastoma

  • Multiple myeloma