The Use of Stem Cells (AQA A Level Biology): Revision Note

Evaluating the use of stem cells

Embryonic stem cells

• Due to their ability to differentiate into multiple cell types, stem cells have huge potential in the treatment of disease and in producing transplant tissues and organs

• The embryos used for research are specifically donated for this purpose by couples who have undergone IVF

• Many countries impose strict regulations on the use of embryonic stem cells

Uses of embryonic stem cells

• Parkinson’s disease: Replace lost dopamine-producing neurons

• Type 1 diabetes: Generate insulin-producing beta cells

• Macular degeneration: Replace damaged retinal cells

• Spinal cord injury: Rebuild nerve connections

Advantages

• They are very versatile as they can become any tissue type

• They offer long-term potential for curative treatments

Disadvantages

• Ethical concerns: Involves the destruction of embryos

• Immune rejection risk: Cells are not genetically matched

• Can form tumours if cell division is not controlled properly

Multipotent adult stem cells

• Adult stem cells can divide (by mitosis) an unlimited number of times, but they are only able to produce a limited range of cell types

• A small number of adult stem cells are found in certain tissues within the body, such as:

  • bone marrow - used to produce different types of blood cells

  • brain - used to produce different types of neural and glial cells

Uses of adult stem cells

• Leukaemia: Bone marrow transplants are used to restore blood cells after chemotherapy

• Burns/skin grafts: Skin stem cells are used for regenerating damaged tissue

• Cartilage/bone repair

Advantages

• No embryo destruction as they are harvested from consenting adults, so there are fewer ethical issues

• Lower risk of immune rejection if from the same patient

Disadvantages

• Many people donate bone marrow (to help treat leukaemia patients), and they need to be a close match in blood type and other body antigens

  • There is a chance that the cells used are rejected by the patient's immune system

• Limited differentiation potential

• They are harder to isolate and grow in large quantities

• They may have accumulated mutations over time

Induced pluripotent stem (iPS) cells

• iPS cells are reprogrammed from adult somatic cells (e.g., skin cells) using transcription factors

• As all somatic cells contain the same genetic material, scientists can use specific transcription factors to target the genes that control pluripotency

  • Scientists 'switch on' these genes that are usually silenced in differentiated cells, which allows them to revert to pluripotent cells

• The resultant pluripotent cells can then be used to produce any cell type required for the repair or treatment of the body

  • iPS cells could therefore be used instead of embryonic cells

• iPS cells are actively used in research, with some early clinical applications already underway

Uses of iPS cells

• Similar to embryonic stem cells:

  • Parkinson’s, diabetes, spinal cord injuries, etc.

• Disease modelling: Create patient-specific cells for studying diseases like Alzheimer’s

• Drug testing: Reducing the need for animal models

Advantages

• No embryo destruction, so there are fewer ethical issues

• iPS cells can be made from the patient’s own cells, so there is no risk of immune rejection

• They are tailored to the individual (personalised medicine)

Disadvantages

• Low efficiency and high cost: Converting adult somatic cells (e.g. skin cells) into iPS cells is very inefficient as only a small fraction of treated cells become pluripotent; there are high costs involved due to specialised transcription factors and careful cell culture conditions

Summary of the evaluation of the use of stem cells