Recently, a good news story was shared from Australia where a man suffering from heart failure survived 100 days with a mechanical heart before receiving a successful donor heart.

In comparison, the first two people who received a pig’s heart survived for about two months.

This got us at Replacing Animal Research thinking about xenotransplant research to solve the issue of donor organ shortages, and specifically why we believe there are more effective ways to address this.

Different Biology

Whilst pigs and humans share a high percentage of our genes, we have significant biological differences and whilst our hearts can be a similar size, there are anatomical differences and differences in the chemicals present on the outside of our cells, which increase the likelihood that a patient’s immune system will reject their organs.

Transplant patients must take immunosuppressant medication to stop their immune system from attacking and rejecting the new and unfamiliar cells. When transplanting an organ between species, the differences are more extreme and, therefore, rejection is far more likely. To address this, scientists are altering pig genes to make their cells more like ours by stopping the cells from ‘expressing’ the chemicals which our immune cells attack.

Concern around Genetic modification

The use of pigs as ‘donors’ of organs does not just involve taking a pig from a farm or another environment and taking their organs. These pigs are lab animals living in sterile conditions (completely unnatural), and they have to be bred from genetically modified lines. They’ve had genes switched off, altered, or added to make their cells more ‘human’ and reduce the chance of rejection in the human body. The pig used to supply the kidney to a man earlier this year had seven humanised genes in their genome, and the pigs used in the heart transplants had ten alternations to their genes.

Whilst gene altering technology has improved, there are still concerns around the precision which can result in unplanned biological changes. This means some animals may not be fit for the purpose they were bred for, and others may suffer as a result of off-target genetic modifications.  Also, the number of animals used in the creation of a new genetically altered line is a concern. Whilst one pig is sacrificed for their heart or kidney, many pigs were used to create them, and the numbers are not always shared or easy to find.

Trials on animals

The other aspect of xenotransplant research that is not often discussed is the transplant of pig organs to other animals prior to humans, normally non-human primates due to their biological similarity to humans. If you consider early trials were less successful  (in 2016 a monkey survives for 51 days as a ‘new record’) and that ‘data from hundreds of baboons’ was used to gain approval for pig to human transplants, you can see that a significant number of pigs and monkeys have been used to get to his point, and may still be used in future to further progress this technology.

Increase Organ donation

45% of the UK population have recorded their decision on whether they wish to donate their organs or not on the UK Organ Donor Register. The Uk has an ‘opt-out’ system whereby those who do not register a decision are presumed to agree to organ donation. However, organ donation only goes ahead with the support of the donors family or loved ones. Registering a decision is an important step in communicating what an individual wants to do.

Organ donation is successful, the NHS report that 85% of patients are alive one year after a heart transplant, and 72% are alive after 5 years.

Putting time, energy and funding into education, communication about organ donation and improving organ donation processes will all help to increase the donor pool.

Modern tissue engineering and 3D bioprinting technologies are allowing more human-relevant, alternative options to be explored as future solutions to organ donation and perhaps mechanical hearts will provide a successful bridging solution for those awaiting a heart transplant.

Although xenotransplantation has been touted as a solution to the organ donation shortage, perhaps we should remember the words of Dr Ian Malcom (Or rather Geoff Goldblum in Jurassic Park):

‘your scientists were so preoccupied with whether or not they could, they never stopped to think if they should’

Further reading:

Why we need to focus on human-relevant science, not try again

The history and ethics of xenotransplants