AVROBIO Gene Therapy Education

AVROBIO Gene Therapy Reference

02 Understanding Cell Therapy

Section 2

Overview of Stem Cells

Learning Goal

To understand the different types of stem cells and how they are used in gene therapy.

Stem cells have been called the body’s “raw materials” for their ability to regenerate and make new types of cells in the body, including red blood cells, which are replaced in the body every 120 days.1-3 Stem cells can divide symmetrically or asymmetrically.4

  • Under symmetric cell division, a stem cell can undergo a process called self-renewal to form two daughter cells, which are copies of itself, or differentiate into specialized cells (also known as differentiated cells) with a more specific function (e.g., blood cells, bone cells, skin cells).1,2,4
  • By contrast, asymmetric cell division is a process by which a stem cell generates one daughter cell and one specialized cell.4

Both types of division – and both types of cells — are important to the body, as daughter cells are essential for repopulating the bone marrow, and specialized cells play key roles in specific body functions.5

Among all cells in the body, stem cells have three unique capabilities2:

  • They can divide and renew themselves over a long period of time
  • They are unspecialized, meaning their use is not limited to performing specific functions in the body
  • They have the potential to differentiate into one or more specialized cell types

There are various types of stem cells that come from different sources:

  • Human embryonic stem cells, which come from embryos, produce all 200 cell types throughout the body. Ethical concerns limit the research and use of embryonic stem cells, and researchers who study them must adhere to strict guidelines.1
  • Adult stem cells’ primary function is to replenish tissue in their associated anatomical locations such as the skin, blood, and the lining of the gut.6,7
    • Hematopoietic stem cells (HSCs) are a type of adult stem cell. These are multipotent, blood-forming stem cells that give rise to all types of blood cells, including red blood cells, white blood cells, and platelets.8
      • HSCs are mostly found in the bone marrow,8 though they also can be harvested from cord blood, the fetal blood that remains in the umbilical cord and placenta post-delivery.9
      • Cord blood banking (also known as stem cell banking) is the process of collecting the cord blood and extracting and freezing HSCs.9

Additional Interesting Fact

Researchers are studying stem cells for a number of potential uses, including1:

  • Increasing understanding of how diseases develop
  • Generating healthy cells to replace diseased cells
  • Testing new drugs for safety and effectiveness
  • Facilitating gene therapy

Key Learnings

Stem cells, known for their ability to develop into many different types of cells in the body, can divide symmetrically or asymmetrically.

  • Symmetric cell division can either result in two daughter cells or two specialized cells (also known as differentiated cells) with a more specific function.
  • Asymmetric cell division results in generation of one daughter cell and one specialized cell.

Human embryonic stem cells differentiate into all 200 different cell types in the body.

Adult stem cells’ primarily function is to replenish tissue in their associated anatomical locations, including skin, blood, and the lining of the gut.

  • Hematopoietic stem and progenitor cells (HSPCs) are multipotent, blood-forming adult stem cells that give rise to all types of blood cells. HSPCs can be harvested from the bone marrow and umbilical cord blood and reserved for potential future medical use.

Continue learning about cell therapy in the next section

Section 3

Overview of Hematopoietic Stem Cells (HSCs)

To understand the function of hematopoietic stem cells

Next Section ››

References

  1. Stem cells: what they are and what they do. Mayo Clinic Website; 2019. https://www.mayoclinic.org/tests-procedures/bone-marrow-transplant/in-depth/stem-cells/art-20048117. Accessed December 22, 2021.
  2. Stem cells. MedlinePlus. U.S. Department of Health and Human Services, National Institutes of Health, U.S. National Library of Medicine; 2021. https://medlineplus.gov/stemcells.html#:~:text=Stem%20cells%20are%20cells%20with,cells%20and%20adult%20stem%20cells. Accessed December 22, 2021.
  3. Arias CF, Arias CF. How do red blood cells know when to die? R Soc Open Sci. 2017;4(4):160850.
  4. Morrison SJ, Kimble J. Asymmetric and symmetric stem-cell divisions in development and cancer. Nature. 2006;441:1068-1074. [PubMed]
  5. Yang J, Plikus MV, Komarova NL. The role of symmetric stem cell divisions in tissue homeostasis. PLoS Comput Biol. 2015;11(12):e1004629. [PubMed]
  6. Stem cell basics. NIH Stem Cell Information Home Page: Stem cell information. U.S. Department of Health and Human Services, National Institutes of Health; 2016. https://stemcells.nih.gov/info/basics/stc-basics/#stc-I. Accessed December 22, 2021.
  7. Types of stem cells. International Society for Stem Cell Research; 2021. https://www.closerlookatstemcells.org/learn-about-stem-cells/types-of-stem-cells/#tissue-specific. Accessed December 22, 2021.
  8. Hematopoietic stem cell. NCI Dictionary of Cancer Terms. U.S. Department of Health and Human Services, National Institutes of Health, National Cancer Institute; 2021. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/hematopoietic-stem-cell. Accessed December 22, 2021.
  9. Cord blood banking: frequently asked questions. American College of Obstetricians and Gynecologists (ACOG); 2021. https://www.acog.org/womens-health/faqs/cord-blood-banking. Accessed December 22, 2021.