Study finds long-term dynamics of transplanted stem cells

For the first time, scientists have tracked what happens to stem cells decades after a transplant, lifting the lid on the procedure that has been a medical mystery for over 50 years. Insights could pave the way for new strategies in donor selection and transplant success, potentially leading to safer, more effective transplants. Researchers were able to map the behaviour of stem cells in recipients’ bodies up to three decades post-transplant, providing the first-ever glimpse into the long-term dynamics of these cells.

The study, published in Nature reveals that transplants from older donors, which are often less successful, have ten times fewer vital stem cells surviving the transplant process. Some of the surviving cells also lose the ability to produce the range of blood cells essential for a robust immune system. Despite being performed for over 50 years, many fundamental questions about how transplants work have remained unanswered. Donor age has been known to impact success rates, but what happens at the cellular level following a transplant has been a ‘black box’, until now.

In this new study, researchers used advanced genome sequencing techniques to analyse blood samples from ten donor-recipient sibling pairs up to 31 years post-transplant. By analysing the mutations that occur throughout life in the donor and recipient’s stem cells, they could track how many stem cells had survived the transplant process and continued to produce new blood cells in the patient’s body — an approach previously impossible.

The team discovered that in transplants from younger donors about 30,000 stem cells survive long-term, compared to only 1-3,000 in older donors. This drop could lead to reduced immunity and higher relapse risk. They also found that the transplant process ages the blood system in recipients by about 10-15 years compared to the matched donors, primarily due to lower stem cell diversity.