Chemotherapy and radiotherapy can kill tumours and the cells which make sperm. A study, published in the journal Cell Stem Cell, extracted sperm-producing stem cells before cancer treatment and later placed them back into the monkey. Sperm which could fertilise an egg were produced.

Most men who have cancer treatment which could affect their fertility can choose to freeze sperm before their treatment starts. This is not an option for patients who have not yet gone through puberty.

However, they do have the spermatogonial stem cells which would start to produce sperm in their teenage years. The researchers at the University of Pittsburgh and the Magee-Womens Research Institute took samples of the stem cells from macaques and stored them in a freezer. The monkeys were then given a chemotherapy drug. Their own stem cells were implanted back where they came from after the course of chemotherapy had ended. Nine out of 12 adult monkeys and three out of five prepubescent monkeys were later able to produce sperm again. Separate experiments showed eggs could be fertilised with sperm produced after the procedure. 

"But also we need to make sure that the genetics of sperm produced from transplanted spermatogonial stem cells is correct and leads to the birth of healthy offspring which themselves give rise to healthy grandchildren and great grandchildren" - sais Dr Allan Pacey.

More information - BBC News.