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3.4.2Topic 3 · Voice of the Genome

Stem Cells in Medicine — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

5 min read 9 parts Lesson 21 of 26 1 quiz

📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision
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3.4.2 Stem Cells in Medicine — Edexcel A Level Biology A (SNAB) 9BI0 notes: Evaluate the use of stem cells in treating disease and in research, including the ethical, social and scientific issues.Many diseases result from the loss or malfunction of particular cells which the body…

  • Bone marrow (haematopoietic stem cell) transplants
  • Skin and cornea repair
  • Experimental treatments
  • Exam-style question 1
  • Exam-style question 2
  • Exam-style question 3

Part 1 of 7Why stem cells are medically useful

Many diseases result from the loss or malfunction of particular cells which the body cannot replace.

Why stem cells are medically useful
If stem cells can be directed to differentiate into the missing cell type and be introduced into the patient, they might restore function.
Research applications include testing new drugs on human tissue grown in culture,
  • and studying how a disease develops using cells from patients,
  • and the processes of normal development.

Part 2 of 7Current and proposed treatments

Current and proposed treatments
Bone marrow (haematopoietic stem cell) transplants
Bone marrow (haematopoietic stem cell) transplants used to treat leukaemia and some inherited blood disorders.
  • The patient's diseased marrow is destroyed by chemotherapy or radiation and replaced with healthy stem cells from a matched donor,
  • which then produce healthy blood cells.
Skin and cornea repair
Skin and cornea repair stem cells grown in the laboratory provide sheets of epithelial cells for burns, and limbal stem cells repair damaged corneas.
Experimental treatments
Experimental treatments research is exploring replacing damaged heart muscle after a heart attack, insulin-producing beta cells in type 1 diabetes, dopamine-producing neurones in Parkinson's disease, retinal cells in macular degeneration,
  • and nerve cells after spinal injury.

A key idea is that tissue matching matters: cells from another person may be recognised as foreign by the immune system, because of different antigens (human leucocyte antigens, HLA) on their surface, and rejected. Patients then need immunosuppressant drugs. Using iPS cells made from the patient's own tissues avoids this.

Part 3 of 7Benefits and risks

BenefitsRisks and limitations
Potential to cure conditions that currently have limited treatmentCells may divide uncontrollably and form tumours (teratomas)
Donor shortages for organs could be reducedRisk of immune rejection with donor cells and of infection by viruses in transplanted cells
Drug testing on human cells reduces the need for animal testingHard to control differentiation reliably and to obtain pure populations
Insight into early human development and the cause of genetic diseaseExpensive, and many treatments remain unproven or untested in humans

Part 4 of 7Ethical and social issues

Using embryonic stem cells involves destroying a blastocyst.

1
People who believe that life begins at fertilisation consider this unacceptable,
  • while others argue that an early embryo of a few hundred cells has no nervous system and no sentience,
    • and that the benefits to many patients outweigh this, especially when the embryos are surplus IVF embryos that would otherwise be discarded.
2
Other issues include informed consent from donors, the possibility of commercial exploitation, fair access to expensive treatments,
  • and the claims made by clinics that offer unregulated treatments.
3
In the UK the use of human embryos is regulated by law and licensed, with research limited to embryos up to 14 days old.
4
Scientists justify research by weighing risks against benefits, using evidence, peer review and public debate.

Part 5 of 7Therapeutic cloning and gene therapy

In therapeutic cloning, the nucleus of a patient's somatic cell is placed into an egg from which the nucleus has been removed, and the egg is stimulated to divide to form an embryo.

Therapeutic cloning and gene therapy
Stem cells from it would be genetically identical to the patient.
Because this involves creating embryos, it raises ethical concerns, and iPS cells are a growing alternative.
Stem cells could also be used with gene therapy: a faulty gene is corrected in the patient's stem cells in the laboratory,
  • and the corrected cells are returned.

Part 6 of 7Exam focus and evaluating claims

In extended-response questions about stem cell therapy, structure your answer with three headings: the scientific evidence, the risks and the ethical issues.

Exam focus and evaluating claims
For the science, say which cells are used and why they are suitable.
For example, haematopoietic stem cells are multipotent and naturally found in bone marrow, so they can regenerate the blood system.
Mention the need for a close HLA match to limit rejection and graft-versus-host disease,
  • where the donated immune cells attack the recipient's tissues.

When asked to evaluate a news report or clinical claim, look at the sample size, whether there was a control group, whether the results were published after peer review, who paid for the research and how long the patients were followed.

Exam focus and evaluating claims
A treatment tested on a few patients without a control group gives weak evidence.
This ability to judge the quality of evidence is as important as the factual content.

Part 7 of 7Exam-style questions

  1. Explain why a bone marrow transplant can be used to treat leukaemia. [3]3 marks

  2. Discuss the ethical arguments for and against the use of human embryonic stem cells in research. [4]4 marks

  3. A patient's own skin cells are reprogrammed to give iPS cells that are then transplanted. Explain why immunosuppressant drugs are unlikely to be needed. [2]2 marks

Key terms

TermMeaning
Haematopoietic stem cellA multipotent cell in bone marrow that gives rise to all blood cell types.
ImmunosuppressantA drug that reduces the activity of the immune system.
TeratomaA tumour that can form from pluripotent cells, containing several tissue types.
Therapeutic cloningCreating an embryo with a patient's DNA to obtain matching stem cells.
HLAHuman leucocyte antigens: surface proteins used by the immune system to identify self.
Informed consentAgreement given with full knowledge of the risks and purposes.

Avoid these mistakes

1
Giving a one-sided answer to 'discuss' questions. Include benefits, risks and at least one ethical viewpoint on each side.
2
Saying that stem cell therapies are already routine for all diseases; only a few, such as blood and skin, are well established.
3
Describing rejection as caused by bacteria. It is the immune response to foreign antigens on the transplanted cells.
4
Stating that embryonic stem cells are 'cloned' in all cases. Most come from surplus IVF embryos.

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