When people hear about stem cells, they tend to think of them as a magical type of cell that can change into any other kind of cell in the human body. Although this is partly true, stem cells are much more specific than that. There are several different types of stem cells, each with its own unique properties and applications in medical research and practice.

Stem cells are so named because they can either divide to produce more copies of themselves or differentiate into more specialized types of cells. Stem cell division produces new stem cells, while differentiation produces new cells with a specialty—for example, bone-making osteoblasts or blood-making red blood cell erythrocytes. Each type of stem cell has properties that distinguish it from other similar styles in the same category. Here are some of the most common types:

Different Types of Stem Cells 

1. Hematopoietic stem cells (HSCs) 
2. Mesenchymal Stem Cells (MSCs)
3. Neural Stem Cells (NSCs)
4. Human Embryonic Stem Cells (hESCs)
5. Induced Pluripotent Stem Cells (iPSCs)

Hematopoietic stem cells (HSCs) 

Hematopoietic stem cells (HSCs) are a type of precursor cell found in the bone marrow that can develop into different kinds of blood cells, such as red blood cells, white blood cells, and platelets. HSCs can self-renew, meaning they can divide and produce copies of themselves.

There are several intermediate progenitor cells between HSCs and mature cells. These cells' multipotent and lineage-committed attributes are usually displayed together or separately before complete maturation. Blood is a highly regenerative tissue thanks to its short lifespan, and BM supports diverse cells' dynamic movement to ensure blood cells' homeostasis.

‍

What are Hematopoietic stem cells used for?

Many non-malignant (e.g., sickle cell disease) and malignant (e.g., leukemia, lymphoma) diseases are treated with HPCs, which replace or rebuild patients' hematopoietic systems. Bone marrow or stem cell transplants can treat patients with non-malignant and malignant diseases. Clinical trials using HPCs for treating autoimmune disorders, genetic diseases, and other problems have been conducted under the supervision of the U.S. FDA. Here are some conditions for which stem cell transplants are an option:

Blood cancers 

Blood cancers cause uncontrolled growth of unhealthy cells in the bone marrow, the factory that makes blood cells. They can broadly be categorized as leukemias, lymphomas, and myelomas.

• Acute lymphoblastic leukemia (ALL)
• Acute myeloid leukemia (AML)
• Chronic lymphocytic leukemia (CLL)
• Chronic myelogenous leukemia (CML)
• Hodgkin lymphoma
• Multiple myeloma
• Myelodysplastic syndromes (MDS)
• Non-Hodgkin lymphoma (NHL)

Non-blood cancers

Blood disorders, immune system disorders, and inherited metabolic disorders.

• Adrenoleukodystrophy (ALD)
• Hurler syndrome
• Krabbe disease (Globoid-Cell Leukodystrophy)
• Metachromatic Leukodystrophy (MLD)
• Severe aplastic anemia
• Severe Combined Immunodeficiency (SCID)
• Sickle cell disease (SCD) 
• Wiskott-Aldrich syndrome (WAS)
  

Mesenchymal Stem Cells (MSCs)

Mesenchymal stem cells (MSCs) are a type of adult stem cell that can differentiate into a wide range of cell types. They are found in many different tissues and can be isolated from almost any source, including bone marrow, fat, umbilical cord, and placenta. MSCs have many possible applications in the medical field, from regenerative medicine to cancer therapy. MSCs can also create biological components such as skin, cartilage, and bone, which can be used to treat patients with severe injuries or diseases. In addition, MSCs are being studied for their potential to treat autoimmune diseases such as Multiple Sclerosis and Crohn's Disease. With all these potential applications, it's no wonder the study of MSCs has become one of the most exciting fields in modern medicine.

For years, researchers believed that mesenchymal stem cells only existed within the bone marrow. However, research has found various sources for MSCs, including umbilical cord tissue, body fat, molar teeth, and amniotic fluid. 

The cells derived from cord tissue, more specifically Wharton's Jelly, are the youngest and most primitive MSCs available. With most umbilical cords discarded after childbirth, this source is non-harmful and readily available. View the source article.

The young nature of these cells allows the enormous potential for them to transform into whatever type of cell is necessary within the body. Youthful cells also tend to replicate faster, and MSCs cannot only differentiate into other cell types but multiply to increase their healing effect on the body. 

What conditions have Mesenchymal Stem Cells been used to treat?

Human mesenchymal stem cells (MSCs) have been used in many clinical studies for the treatment of immune and inflammation-related diseases, including the following:

• Cardiovascular conditions: Various types of drug-induced ischemic cardiomyopathy, chronic heart failure, myocardial infarction, and atherosclerotic plaque.
• Neurological conditions: Hypoxic-ischemic brain lesions, Parkinson's Disease, Stroke, ALS, Multiple Sclerosis, and Alzheimer's disease.
  
• Orthopedic conditions: Osteochondral defects, Arthritis and Osteoarthritis.
• Rheumatologic conditions: Rheumatoid arthritis, ankylosing spondylitis, lupus erythematosus, systemic sclerosis,  polymyositis and dermatomyositis, and Sjögren's syndrome.
  
• Endocrine diseases: Type 1 diabetes mellitus.
  
• Autoimmune / Inflammatory conditions: Crohn's Disease, Post Treatment Lyme Disease Syndrome, Long COVID, Fibromyalgia, COPD, and other inflammatory lung conditions.
  

It is foreseen that mesenchymal stem cells will provide significant therapeutic benefits to many patients based on the results of the published studies and ongoing trials available.

Neural Stem Cells (NSCs)

Specialized stem cells are responsible for repairing nerve-insulating myelin in the brain. These can be derived from other types of stem cells, such as mesenchymal cells.

In adults, only a tiny number of NSCs remain and are primarily inactive; however, there is substantial supporting evidence for their crucial roles in the nervous system's plasticity, aging, disease, and regeneration. NSCs are controlled by intrinsic genetic and epigenetic programs and extrinsic environmental stimuli transmitted by the stem cell niche. 

A genetic defect or environmental factor might cause disease. Due to their importance, considerable research has been conducted to determine how NSCs are controlled. Since they were first discovered, NSCs have been a focal point for cell-based therapy in the brain and spinal cord. Despite recent advancements in mesenchymal, embryonic, and induced pluripotent stem cells, several challenges remain. The restricted number of surviving NSCs has limited their clinical applications. (2)

Human Embryonic Stem Cells (hESCs)

Stem cells are derived from donated embryos. They can naturally produce every type of cell in the body. One concern about their potential therapeutic use is that they have been found to cause tumors.

Human embryonic stem cells, commonly called hESCs, can self-renew and produce new adult tissues of various differentiation potentials. These properties make hESCs extremely promising for regenerative medicine applications. However, their use in human clinical trials is limited by their ethical origins and the need for effective methods to generate sufficient quantities of pure and stable hESCs.

Human embryonic stem cells are derived from the inner cell mass of a developing blastocyst. Research involving hESC lines has been greatly limited by the ethical debate over using human embryos for research purposes. Most hESC lines available today were obtained before the 2001 revisions to the Common Rule that governs clinical research with humans (also known as "human subjects" research). These changes have led researchers to shy away from continuing work on hESCs due to concerns about the possible negative impact on their careers or reputation. However, others have found ways around this contentious ethical dilemma through alternate sources of hESC lines and novel techniques for culturing them outside human embryos.

‍

Induced Pluripotent Stem Cells (iPSCs)

Induced pluripotent stem cells (iPSCs) are adult cells reprogrammed to a state similar to an embryonic stem cell. This process is referred to as "induced" because it requires the introduction of specific proteins and factors to coax the adult cells into becoming pluripotent.

iPSCs were first described by Shinya Yamanaka and his colleagues at Kyoto University in 2006. They were jointly awarded the 2012 Nobel Prize in Physiology or Medicine for their work. These reprogrammed adult cells offer many advantages over embryonic stem cells, including reduced risk of immune rejection, simplified ethical concerns, and less stringent cryogenic requirements. Moreover, iPSCs can be derived from individuals with a pre-existing threat of developing diseases caused by mutations in their germline DNA (e.g., certain genetic disorders). One concern about their potential therapeutic use is that they have been found to cause tumors.

Conclusion

Stem cell therapies are one promising front in the ongoing war against diseases and diseases of aging. As this article discusses, stem cells can potentially treat various conditions, including diabetes, heart disease, dementia, and transplant rejection. While these are exciting potential applications, a few key factors need to be considered before implementing stem cell therapies into practice.

Many different types of stem cells can differentiate into other cell types and offer the possibility of cell replacement therapies, tissue repair, and the development of new organs. 

HSCs have the longest track record of use in humans; they have been used in various clinical trials for over 40 years, but they have yet to be ready to be used on an approved basis.

Mesenchymal stem cells (MSCs) are the most studied type of stem cell. They come from many tissue types across the body and display the most comprehensive range of differentiation potential. Like HSCs, MSCs are responsible for producing new cells in the body. They have been used in several clinical trials to treat Heart Disease, Stroke, Multiple Sclerosis, Parkinson's Disease, and Diabetes.

References: 

(1) Baykal, B. (n.d.). Mesenchymal stem cells for the treatment of various diseases. Open Access Text. Retrieved November 29, 2022, from https://www.oatext.com/Mesenchymal-stem-cells-for-the-treatment-of-various-diseases.php

(2) Zhao, X., & Moore, D. L. (2018, January). Neural stem cells: Developmental mechanisms and disease modeling. Cell and tissue research. Retrieved November 29, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5963504/#:~:text=Neural%20stem%20cells%20(NSCs)%20are,to%20the%20entire%20nervous%20system.