Is it possible to become immortal with the help of organ transplants? That was the unexpected topic of discussion this week between Chinese President Xi Jinping and Russian President Vladimir Putin when they met at a military parade in Beijing.
A translator, speaking in Mandarin on behalf of Putin, told Xi how human organs can be repeatedly transplanted so that one can get younger and younger in spite of age, and might even be able to stave off old age indefinitely.
It's predicted that in this century it might become possible to live to 150, he added.
Their smiles and laughter suggest it was a bit of banter, but might they be onto something?
Organ transplants certainly save lives - in the UK, over 100,000 people have been saved in the last 30 years, says NHS Blood and Transplant.
And continued advancements in medicine and technology mean transplanted organs last longer once in people.
Some patients have had a kidney transplant that has kept working for more than 50 years.
The lifespan of an organ depends on how healthy the donor and recipient is - plus how well they look after it. For example, if you were to have a new kidney from a living donor, you might expect it to last 20 to 25 years. If you get it from a deceased donor, that drops to 15 to 20 years.
The type of organ matters too.
A liver might last around 20 years, a heart 15 years and lungs nearly 10 years, according to research.
Putin and Xi may be talking about having multiple organs transplanted and perhaps repeatedly. Having surgery is a big undertaking, though, with significant risks. Each time you go under the knife, you are rolling the dice.
Currently, people who get a new organ also have to take strong anti-rejection drugs called immunosuppressants for life. These can have side-effects, such as high blood pressure, and increase the risk of infections.
Rejection - when your immune system starts to attack the transplanted organ because it recognises it as coming from a different person - can sometimes still happen even if you are taking your medication.
Scientists are working on making rejection-free organs, using genetically-altered pigs as the donors.
They use a gene editing tool known as crispr to remove some of the pig genes and add certain human genes to make the organ more compatible.
Breeding special pigs for this is ideal since their organs are roughly the right size for humans.
The science is still extremely experimental, but a heart and a kidney operation have gone ahead. The two men who agreed to having the procedures were pioneers of this new field of transplantation medicine, having both since died but helped advance xenotransplantation - the transplanting of living cells, tissues or organs from one species to another.
Yet, the advances are for treating ill health rather than keeping people alive to 150 years.
Tech entrepreneur Bryan Johnson is spending millions a year trying to reduce his biological age. He's infused himself with his 17-year-old son's plasma but has since stopped that after seeing no benefits and increased scrutiny from organizations such as the Food and Drug Administration.
Experts express skepticism about whether such experimental strategies will substantially impact lifespan. Prof Neil Mabbott postulates that living to 125 years old might be the upper limit, highlighting that the oldest verified person lived to be 122.
While new organ technology may save lives, focusing on extending lifespan raises concerns regarding the quality of life and health challenges associated with aging, rather than simply adding years to a life burdened with health complications. Living longer but suffering from multiple health issues does not appear an attractive option.
