Topic 8—-A: Mutations and gene expression- 6. Stem cells in medicine

Question 1

Bone marrow transplants

Answer 1

• bone marrow contains stem cells that can become specialised to form any type of blood cell
• bone marrow transplants can be used to replace the faulty bone marrow in patients that produce abnormal blood cells
• The stem cells in the transplanted bone marrow divide and specialise to produce a healthy blood cells
• this technique has been used successfully to treat leukaemia ( a cancer of the blood or bone marrow ) and lymphoma ( a cancer of the lymphatic system )
• it has also been used to treat some genetic disorders such as sickle-cell anaemia and severe combined immunodeficiency (SCID)

Question 2

Example- SCID

Answer 2

• Severe combined immunodeficiency (SCID) is a genetic disorder that affects the immune system
• people with SCID have a poorly functioning immune system as their white blood cells (made in the bone marrow from stem cells) are defective
• this means they can’t defend the body against infections by identifying and destroying microorganisms
• so SCID sufferers are extremely susceptible to infections
• treatment with a bone marrow transplant replaces the faulty bone marrow with donor bone marrow that contains stem cells without the faulty genes that cause SCID
• These then can differentiate to produce functional white blood cells
• these cells can identify and destroy invading pathogens, so the immune system functions properly

Question 3

Scientists are researching the use of stem cells as treatment for lots on conditions including:

Answer 3

• spinal cord injuries: stem cells could be used to replace damaged nerve tissue
• heart disease and damage caused by heart attacks: stem cells could be used to replace damaged heart tissue
• bladder conditions: stem cells could be used to grow whole bladder, which are then implanted in patients to replace diseased ones
• respiratory diseases: donated windpipes can be stripped down to their simple collagen structure and then be covered with tissue generated by stem cells. This can then be transplanted into patients
• organ transplants: organs could be grown from stem cells to provide new organs for people on donor waiting lists

Question 4

What are the sources of human stem cells?

Answer 4

• adult stem cells
• embryonic stem cells
• induced pluripotent stem cells (iPS)

Question 5

Adult stem cells

Answer 5

• obtained from the body tissues of an adult
• e.g. adult stem cells are found in bone marrow
• they can be obtained in a relatively simple operation- with very little risk involved but quite a lot of discomfort
• adult stem cells aren’t as flexible as embryonic stem cells- they can only specialise into a limited range of cells, not all body cell types (they’re multipotent)
• although scientists are trying to find ways to make adult stem cells specialise into any cell type

Question 6

Embryonic stem cells

Answer 6

• obtained from the embryos at an early stage of development
• embryos are created in a laboratory using in vitro fertilisation (ivf)- egg cells are fertilised by sperm outside the womb
• once the embryos are approximately 4-5 days old stem cells are removed from them and the rest of the embryo is destroyed
• embryonic stem cells can divide an unlimited number of times and develop into all type of body cells (they’re pluripotent)

Question 7

Induced pluripotent stem cells (iPS cells)

Answer 7

• IPs cells are created by scientists in the lab
• the process involves reprogramming specialised adult body cells so that they become pluripotent
• the adult stem cells are made to express a series of transcription factors that are normally associated with pluripotent stem cells
• the transcription factors cause the adult body cells to express genes that are associated with pluripoteny
• one of the ways that these transcription factors can be introduced to the adult cells is by infecting them with a specially-modified virus
• the virus has the genes coding for the transcription factors within its DNA
• When the virus infects the adult cell, these genes are passed into the adult cells dna meaning that the cell is able to produce the transcription factors
• induced pluripotent stem cells could become really useful in research and medicine in the future
• at the moment, more research into how similar they actually are to true pluripotent embryonic stem cells is needed before they can be properly utilised

Question 8

Ethical considerations (stem cells)

Answer 8

• obtaining stem cells from embryos created by IVF raises ethical issues because the procedure results in the destruction of an embryo that could become a fetus if placed in a womb
• some people believe that at the moment of fertilisation an individual is formed that has the right to life- so they believe that its wrong to destroy embryos
• some people have fewer objections to stem cells being obtained from eggs cells that haven’t been fertilised by sperm, but have been artificially activated to start dividing - this is because the cells couldn’t survive past a few days and wouldn’t produce a fetus if placed in a womb
• some people think that scientists should only use adult stem cells because their production doesn’t destroy an embryo- but adult stem cells can’t develop into all the specialised cell types that embryonic stem cells can
• this is where induced pluripotent stem cells could prove really useful
• they have the potential to be as flexible as embryonic stem cells but as they’re obtained from adult tissue there aren’t the same ethical issues surrounding their use
• its also possible that IPs cells could be made from a patients ow cells
• these IPs cells which would be genetically identical to the patients cells , could then be used to grow some new tissue or an organ that the patients body wouldn’t reject (rejection of transplants occurs quite often and is caused by the patients immune system recognising the tissue as foreign and attacking git
• the decision makers in society have to take into account everyone’s views when making decisions about important scientific work like stem cell research and its use to treat human disorders

Question 9

Benefits of stem cell therapy

Answer 9

• they could save so many lives: e.g. many people waiting for organ transplants die before a donor organ becomes available. Stem cells could be used to grow organs for those people awaiting transplants
• it might even be possible to male stem cells genetically identical to a patients own cells. These could dthen be used to grow some new tissue or an organ that the patients body wouldn’t reject
• they could improve the quality of life for many people: e.g. they could be used to replace damaged cells in the eyes of people who are blind