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 on to 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 are lasting far 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,

© BBC