Rare stem cells discovered that help to produce new sperm have the potential to cure infertility in cancer patients, scientists have said.

Researchers have found stem cells in testes that produce a biomarker protein called PAX7, which help produce new sperm cells in mice.

In the US, infertility affects about 4.7 million men and it is a major side effect of cancer treatments such as radiation and chemotherapy.

The team, from the University of Texas Southwestern Medical Centre, found that unlike similar cells that develop into sperm, the PAX7 stem cells were able to survive treatment with toxic drugs and radiation.

Even after exposure to chemotherapy and radiation treatment, the PAX7 cells continued to divide and therefore could contribute to restoring sperm development.

Published in the Journal of Clinical Investigation, researchers believe that if their findings are replicated in humans, it could lead to new ways to restore or protect men undergoing cancer treatment from infertility.

Diego H Castrillon, one of the study authors, said: "Unfortunately, many cancer treatments negatively impact fertility, and men who receive such treatments are at high risk of losing their fertility. This is of great concern among cancer patients. The PAX7 stem cells we identified proved highly resistant to cancer treatments, suggesting that they may be the cells responsible for the recovery of fertility following such treatments.

"We have long known that male fertility is driven by rare stem cells within the testes, but the precise identity of these stem cells has been disputed. Our findings suggest that these rare PAX7 cells are the key cells within the testes that are ultimately responsible for male fertility."

The study concluded: "Remarkably, murine PAX7 spermatogonia proved resistant to both radiotherapy and chemotherapy. They not only survived the immediate aftermath of these genotoxic insults, but also rapidly expanded, forming clusters of PAX7 spermatogonia never observed in normal, untreated mice.

"In closing, PAX7 spermatogonia represent a rare but functionally important stem cell population in the healthy adult testis, and also serve an important role in spermatogenic recovery following injury to the germline, such as occurs after chemotherapy or radiotherapy."