Stem cell line

A stem cell line is a group of stem cells that is cultured in vitro and can be propagated indefinitely. Stem cell lines are derived from either animal or human tissues and come from one of three sources: embryonic stem cells, adult stem cells, or induced stem cells. They are commonly used in research and regenerative medicine.

Properties

Main article: Stem cell

By definition, stem cells possess two properties: (1) they can self-renew, which means that they can divide indefinitely while remaining in an undifferentiated state; and (2) they are pluripotent or multipotent, which means that they can differentiate to form specialized cell types. Due to the self-renewal capacity of stem cells, a stem cell line can be cultured in vitro indefinitely.

A stem cell line is distinctly different from an immortalized cell line, such as the HeLa line. While stem cells can propagate indefinitely in culture due to their inherent properties, immortalized cells would not normally divide indefinitely but have gained this ability due to mutation. Immortalized cell lines can be generated from cells isolated from tumors, or mutations can be introduced to make the cells immortal.[1]

A stem cell line is also distinct from primary cells. Primary cells are cells that have been isolated and then used immediately. Primary cells cannot divide indefinitely and thus cannot be cultured for long periods of time in vitro.

Types and methods of derivation

Embryonic stem cell line

Main article: Embryonic stem cell

An embryonic stem cell line is created from cells derived from the inner cell mass of a blastocyst, an early stage, pre-implantation embryo.[2] In humans, the blastocyst stage occurs 4–5 days post fertilization. To create an embryonic stem cell line, the inner cell mass is removed from the blastocyst, separated from the trophoectoderm, and cultured on a layer of supportive cells in vitro. In the derivation of human embryonic stem cell lines, embryos leftover from in vitro fertilization (IVF) procedures are used. The fact that the embryo is destroyed during the process has raised controversy and ethical concerns.

Embryonic stem cells are pluripotent, meaning they can differentiate to form all cell types in the body. In vitro, embryonic stem cells can be cultured under defined conditions to keep them in their pluripotent state, or they can be stimulated with biochemical and physical cues to differentiate them to different cell types.

Adult stem cell line

Main article: Adult stem cell

Adult stem cells are found in juvenile or adult tissues. Adult stem cells are multipotent: they can generate a limited number of differentiated cell types (unlike pluripotent embryonic stem cells). Types of adult stem cells include hematopoietic stem cells and mesenchymal stem cells. Hematopoetic stem cells are found in the bone marrow and generate all cells of the immune system all blood cell types. Mesenchymal stem cells are found in umbilical cord blood, amniotic fluid, and adipose tissue and can generate a number of cell types, including osteoblasts, chondrocytes, and adipocytes. In medicine, adult stem cells are mostly commonly used in bone marrow transplants to treat many bone and blood cancers as well as some autoimmune diseases.[3] (See Hematopoietic stem cell transplantation)

Of the types of adult stem cells have successfully been isolated and identified, only mesenchymal stem cells can successfully be grown in culture for long periods of time. Other adult stem cell types, such as hematopoietic stem cells, are difficult to grow and propagate in vitro.[4] Identifying methods for maintaining hematopoietic stem cells in vitro is an active area of research. Thus, while mesenchymal stem cell lines exist, other types of adult stem cells that are grown in vitro can better be classified as primary cells.

Induced pluripotent stem cell (iPSC) line

Main articles: Induced pluripotent stem cells and Induced stem cells

Induced pluripotent stem cell (iPSC) lines are pluripotent stem cells that have been generated from adult/somatic cells. The method of generating iPSCs was developed by Shinya Yamanaka's lab in 2006; his group demonstrated that the introduction of four specific genes could induce somatic cells to revert to a pluripotent stem cell state.[5]

Compared to embryonic stem cell lines, iPSC lines are also pluripotent in nature but can be derived without the use of human embryos—a process that has raised ethical concerns. Furthermore, patient-specific iPSC cell lines can be generated—that is, cell lines that are genetically matched to an individual. Patient-specific iPSC lines have been generated for the purposes of studying diseases[6] and for developing patient-specific medical therapies.

Methods of Culture

Main article: Cell culture

Stem cell lines are grown and maintained at specific temperature and atmospheric conditions (37 degrees Celsius and 5% CO2) in incubators. Culture conditions such as the cell growth medium and surface on which cells are grown vary widely depending on the specific stem cell line. Different biochemical factors can be added to the medium to control the cell phenotype—for example to keep stem cells in a pluripotent state or to differentiate them to a specific cell type.

Uses

Stem cell lines are used in research and regenerative medicine. They can be used to study stem cell biology and early human development. In the field of regenerative medicine, it has been proposed that stem cells be used in cell-based therapies to replace injured or diseased cells and tissues. Examples of conditions that researchers are working to develop stem cell based treatments for include neurodegenerative diseases, diabetes, and spinal cord injuries.

Ethical issues

Main article: Stem cell controversy

There is controversy associated with the derivation and use of human embryonic stem cell lines. This controversy stems from the fact that derivation of human embryonic stem cells requires the destruction of a blastocyst-stage, pre-implantation human embryo. There is a wide range of viewpoints regarding the moral consideration that blastocyst-stage human embryos should be given.[7][8]

Access to human embryonic stem cell lines

United States

In the United States, Executive Order 13505 established that federal money can be used for research in which approved human embryonic stem cell (hESC) lines are used, but it cannot be used to derive new lines.[9] The National Institutes of Health (NIH) Guidelines on Human Stem Cell Research, effective July 7, 2009, implemented the Executive Order 13505 by establishing criteria which hESC lines must meet to be approved for funding.[10] The NIH Human Embryonic Stem Cell Registry can be accessed online and has updated information on cell lines eligible for NIH funding.[11] There are 279 approved lines as of April 2014.

Studies have found that approved hESC lines are not uniformly used in the U.S. Data from cell banks and surveys of researchers indicate that only a handful of the available hESC lines are routinely used in research. Access and utility are cited as the two primary factors influencing what hESC lines scientists choose to work with.[12]

A 2011 survey of stem cell scientists in the U.S. who use hESC lines in their research found that 54% of respondents used two or fewer lines and 75% used three or fewer lines.[13]

Another study tracked cell line requests fulfilled from the largest US repositories, the National Stem Cell Bank (NSCB) and the Harvard Stem Cell Institute (HSCI; Cambridge, MA, USA), for the periods March 1999 – December 2008 (for NSCB) and April 2004 – December 2008 (for HSCI).[14] For NSCB, out of twenty-one approved cell lines, 77% of requests were for two of the lines (H1 and H9). For HSCI, out of the 17 lines requested more than once, 24.7% of requests were for the two most commonly requested lines.

See also

References

  1. ↑ Irfan Magsood, M; M. M.; Bahrami, A. R.; Ghasroldasht, M. M. (2013). "Immortality of cell lines: Challenges and advantages of establishment". Cell Biology International 37 (10): 1038–1045. doi:10.1002/cbin.10137. PMID 23723166.
  2. ↑ Thomson, JA; Itskovitz-Eldor J; Shapiro SS; Waknitz MA; Swiergiel JJ; Marshall VS; Jones JM (November 6, 1998). "Embryonic stem cell lines derived from human blastocysts". Science. 282 6 (5391): 1145–1147. doi:10.1126/science.282.5391.1145. PMID 9804556.
  3. ↑ http://stemcells.nih.gov/info/basics/pages/basics4.aspx. Missing or empty |title= (help)
  4. ↑ Walasek, MA; van Os R; de Haan G (August 2012). "Hematopoietic stem cell expansion: challenges and opportunities". Ann N Y Acad Sci (1266): 138–150.
  5. ↑ Takahashi, Katzutoshi; Shinya Yamanaka (August 25, 2006). "Induction of Pluripotent Stem Cells from Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors". Cell 126 (4): 663–676pmid=16904174. doi:10.1016/j.cell.2006.07.024. PMID 16904174.
  6. ↑ Park, IH; Arora, N; Huo, H; Maherali, N; Ahfeldt, T; Shimamura, A; Lensch, MW; Cowan, C; Hochedlinger, K; Daley, GQ (September 5, 2008). "Disease-specific induced pluripotent stem cells". Cell 134 (5): 877–886. doi:10.1016/j.cell.2008.07.041. PMC 2633781. PMID 18691744.
  7. ↑ George, Robert P; Alfonso Gomez-Lobo (2005). "The Moral Status of the Human Embryo". Perspectives in Biology and Medicine 48 (2): 201–210. doi:10.1353/pbm.2005.0052.
  8. ↑ Cohen, Cynthia B (June 25, 2007). Renewing the Stuff of Life: Stem Cells, Ethics, and Public Policy. Oxford University Press. ISBN 9780195305241.
  9. ↑ "Executive Order: Removing barriers to responsible scientific research involving human stem cells". The White House.
  10. ↑ "National Institutes of Health Guidelines on Human Stem Cell Research". Retrieved 24 April 2014.
  11. ↑ "NIH Human Embryonic Stem Cell Registry". Retrieved 24 April 2014.
  12. ↑ Levine, Aaron D (December 2011). "Access to human embryonic stem cell lines". Nature Biotechnology 29 (12): 1079–1081. doi:10.1038/nbt.2029.
  13. ↑ Levine, Aaron D (December 2011). "Access to human embryonic stem cell lines". Nature Biotechnology 29 (12): 1079–1081. doi:10.1038/nbt.2029.
  14. ↑ Christopher, Thomas Scott; Jennifer B. McCormick; Jason Owen-Smith (August 2009). "And then there were two: use of hESC lines". Nature Biotechnology 27 (8): 696–697. doi:10.1038/nbt0809-696.