Sperm stem cells from mice were successful in colonizing the animals’ testicles even after being frozen for 23 years, according to research published this Tuesday (10) in the scientific journal Plos Biology.
In the future, the discovery could be useful, the scientists project, for children and adolescents who need to undergo cancer treatment and, sometimes, have their reproductive capacity compromised in adulthood.
Stem cells have, as a definition, the possibility of developing into other cell types, being interesting for tissue regeneration studies, for example.
“There are experiments where you take a stem cell [no inÃcio da formação do organismo] and, when placing it in muscles, it also becomes muscle”, explains Stênio de Cássio Zequi, leader of the Reference Center for Urological Tumors at the ACCamargo Cancer Center, who was not involved in the study.
In the case of this research, the scientists used stem cells specific to the formation of a sperm – they are called spermatogonial stem cells (SSC).
These cells are essential for the initiation of spermatogenesis, the process in the testes that leads to the production of sperm.
When a person needs to undergo cancer treatment, such as chemotherapy, however, this stage of development can be impaired. This occurs, says Zequi, because the therapeutic mechanism acts on all cells that are constantly renewed, as is the case with malignant tumor cells and also reproductive cells. Thus, chemotherapy causes infertility in patients.
For adult men, it is possible to opt for semen freezing, since some can remain sterile even after the end of therapy – according to Zequi, about 50% to 80% manage to regain their reproductive capacity.
But this is not the case for children, as they do not yet have a mature reproductive system. “The reproductive system is mature at puberty, it is not fully developed in the child. It also does not ejaculate, so there is no way to collect semen,” she says.
As a result, some young people who are diagnosed with cancer and undergo aggressive treatment may lose fertility altogether.
The idea of ​​the study was to find a solution to this problem. As the scientists focused on SSCs, this pathway could be used in these children because the cells could be harvested before chemotherapy, frozen and then transplanted into the patient in order to regain the ability to reproduce.
Renato Fraietta, professor of human reproduction at Unifesp (Federal University of São Paulo), explains that this type of research “is the most promising”. Normally, there are two possibilities: the first involves thawing the stem cell and maturing it before transplanting it into an organism, and the second involves directly grafting it into a living being to see if colonization occurs in the testes.
The newly published research followed this second alternative and made use of mice. In addition, the researchers used three groups of SSCs: the first had the cells frozen for more than 23 years, the second for 1 to 4 months, and the last had the cells removed on the day of the analysis itself.
After that, each of these cell groups were transplanted into recipient mice. It was observed that all groups were able to colonize the testicles of the animals, representing the beginning of the sperm formation process.
According to the authors, cells taken on the day of analysis showed a similar ability to form colonies as cells frozen 23 years ago.
“It is a great first step that shows the ability of the stem cell to return to activity when placed in the recipient tissue”, completes Zequi.
However, the discovery does not indicate that the frozen cells necessarily resulted in sperm capable of fertilizing an egg, since production involves 13 stages — the stem cells are in the first stage.
In the article, it is explained that the long-term frozen cell group performed less well in producing healthy sperm compared to the other two groups. For that reason, the authors themselves point out the need for more studies to prove that the discovery can really have an important meaning in reproductive capacity.
This point is also reiterated by Fraietta. He points out that, at the moment, all this research is still experimental, but “a few years from now, when this boy [que passou por tratamento de câncer na atualidade] is an adult and wants to have children, we hope that this technology is already more advanced”.
The professor points out that other studies have already shown some success. One, also mentioned in the newly published research, involved an experiment in mice in which fertility was restored after stem cell transplantation. “But we don’t have that in humans”, concludes Fraietta.
