The research aims to develop treatments to preserve the fertility of boys who are too young to produce sperm for freezing prior to treatments that can cause infertility, such as chemotherapy, radiotherapy or stem cell transplants.
'This advance is an important step toward offering young cancer patients around the world a chance at having a family in the future,' said study senior author Professor Kyle Orwig, from the University of Pittsburgh School of Medicine.
Professor Orwig's team removed the testes of five pre-pubertal monkeys, making them infertile. They then cut the testicular tissue into smaller pieces and some of the tissue samples were kept fresh, while the remaining tissue was cryopreserved.
The scientists then grafted the fresh and cryopreserved testicular tissue under the skin of the monkeys' scrotum or under the skin on their backs. Eight to 12 months following transplantation, the tissue grafts were recovered and the researchers found that sperm was being produced by the grafted testicular tissue.
'We grafted tissue that had zero sperm at the beginning of the experiment, and when we collected the grafts, they were producing millions and millions of sperm,' Professor Orwig told Scientific American.
Sperm produced by the testicular tissue grafts was used to fertilise 138 eggs using the via ICSI. Sixteen embryos were produced, of which 11 were implanted into six female monkeys one of which resulted in the birth of Grady.
The technique that the researchers used, published in the journal Science, to produce baby Grady could potentially be translated into the clinic to preserve the fertility of pre-pubertal boys. However, before moving into humans, the experiments would need to be repeated using non-castrated animals as this would be more representative of patients in the clinic.
This approach may not be suitable for all childhood cancer survivors as cancerous cells may be present in the testicular tissue before treatment, and could risk re-introducing cancerous cells into their body when the graft is replaced.
'This is a really excellent study, which is a great step forward, but it is important to remember that before we could attempt to use it in humans, further research would be needed to show that it is safe and that it works in the same kind of way,' Professor Allan Pacey, professor of andrology at the University of Sheffield, who was not involved in the study, told the BBC. 'This, I think, is still a number of years away.'