XenotransplantationApplications

Year 13 –Biotechnology

Learning IntentionsToday we will:Describe Xenotransplantation and examplesDiscuss the human need and demand for this

applicationComplete a jigsaw reading activity and

report back to class.Examine risks, ethical considerations and

alternatives.

What is it?Xenotransplantation is the transplantation of organs, tissues or cells from ONE SPECIES to ANOTHER.

Human to Human transplants are called allotransplantation

Examples Replace diseased organs

(inert heart valves)Spinal cord injuriesFetal pig cells for

Parkinson’s disease, stroke, epilepsy, Huntington’s disease

Pancreatic cells for Diabetics

Tissue for human bones and skin is being grown and developed from pigs.

Human demandAbout 400 New Zealanders are on the

waiting list for an organ transplant at any one time.... Many die waiting for a suitable donor.

the American Heart Association reports only 2,300 of the 40,000 Americans who needed a new heart in 1997 got one.

The estimate is that demand for organs is growing at 15% per year. Why? - many of today’s health problems are generated by our lifestyles, but we are also living longer.

With ANY organ transplant there is a risk of immune rejection.

Why animal tissues?Xenotransplantation is considered for organ replacement as there is a shortage of willing organ donors

Why pigs and not primates?Pigs are domesticated, breed well in

captivity and have organs of a similar size.

They are DISTINCT enough from humans to reduce the risk of cross species infection by viruses.

3 categoriesAET’s(Animal External therapies)Occurs outside recipients body, i.e blood

passed through machine containing porcine hepatocytes (pig liver cells) to remove toxic substances and then returned to body.

Or human skin grown over layer animal cells and used as graft to treat burns.

ACT’s (Animal Cell therapies)Transplantation of skin, bone marrow or

specialist cells (brain for Parkinsons, pancreatic for Diabetics)

AOT’s (Animal Organ transplants)Transplantation of entire organs (hearts,

lungs, kidneys)

Jigsaw Activity – Article.2min

• Anticipatory guide – tick 1-7 (agree/disagree)• In pairs you will be assigned to an expert group 1 to

5

10min

• As a pair you will read your allocated section and note key information.

2min

• You will have a few more minutes to discuss your notes and ideas

10min

• One person from each pair will report back to the class and the class will complete record sheet to have full overview

2min

• Anticipatory guide – revise and add notes.

Preventing organ rejectionThe immune system is highly specialised

to recognise and attack foreign cells.The risk of rejection is reduced if

transplant tissues match host tissues as closely as possible.

The DONOR and RECIPIENT must share most of the same characteristics such as blood type and Rhesus factor.

Immunosuppressive drugs – reduce the ability of the immune system to attack transplanted cells.BUT these drugs also reduce immune systems ability to fight off other infections

A PERVy ProblemA risk from Xenotransplantation (XT) are pathogens from

donor species.Many pigs carry PERV (Porcine Endogenous

Retrovirus)Trials with mice showed PERV infection....however there

were no infections in human recipients of pig Xenotranplants.

IF virus crossed the species barrier, it could mutate and become more contagious. Cross species infections are known as ZOONOSISExamples – AIDS, BSE, Ebola, Flu epidemics

Increasing donation rates.Australia and NZ have low donation rates (i.e

10.2 per million pop) compared with Spain (33.2) attributed to national transplant organisation set up in 1989)

France, Belgium, Norway and Austria have adopted a ‘presumed consent’ system of organ donation. This means that they will be used for organ donation unless they ‘opt out’. This can considered an unethical approach.

Bioethics council NZIn Feb 2005, the council called for public submission

over cultural, spiritual and ethical concerns.Restrictions on XT’s in NZ were imposed in 2002

with a 3 year ‘sunset clause’ so that NZers were not denied access to XT if it was shown to be safe and offered improved health outcomes.

The law expired in June 2005 and NZ Bioethics council recommended that XT be allowed to develop in NZ

World Health Organisation

Stronger measures needed by countries to stop illegal performance of xenotransplantation

Updated guidelines and reccommendations

Improving methods for collection and dissemination of information practices, successes and risks

Raising greater awareness and promoting high ethical standards.

(more info at: www.who.int/transplantation/xeno)

Recognised need for tougher controls of XT research and following international panel of experts issued plan:

Ethical considerationsThe welfare implications for animalsWhether we have the right to use pigs in this way. Undesirable crossing of the human-animal

boundary. Pigs are considered unclean in some cultures (inc

Judaism/Islam)Perhaps people would accept a xenotransplant but

later feel awful about the thought of a pig heart (or whatever) inside them.

Perhaps it would be better if we put the effort into public health campaigns.

Ethical considerations – Animal rights

The ‘Diaries of Despair’ is a report written by UK group ‘Uncaged’ about Xeno research in 2000.

This example is of observations of a baboon who was the recipient of a hererotopic pigs heart.

‘’One of the most unfortunate animals had a piglet heart transplanted into his neck. It was a particularly disturbing example, I think, because for several days he was holding the heart. It was swollen. It was seeping blood. He suffered from body tremors, vomiting, diarrhoea. And the animal just sat there.I think living hell is really the only sort of real way you can get close to describing what it must be like to have been that animal in that situation’’ (Dan Lyons, director of UNCAGED Campaigns UK)

Are there alternatives?Mechanical artificial body parts for some

disorders.Tissue engineering, Gene therapy and stem cell

research are being combined to develop semi-synthetic living organs.

No risk of zoonosis and less likely to be rejected (less need for immunosuppressants)

We will discuss these in further detail in future lessons..

If anyone is interested in finding out more, please visit websites on ‘Debating society’ resource (handout) or refer to further reading on jigsaw activity