Surrogate testes: Allogeneic spermatogonial stem cell transplantation within an encapsulation device may restore male fertility.

Toxic insult to the gonads by chemotherapy or radiotherapy can lead to permanent infertility. It's an important health concern because each year more than 4000 male patients are at risk of azoospermia in the United States due to gonadotoxicity of the regimens used. There are also several benign/genetic diseases whose natural course can result in infertility without gonadotoxic therapy. Considering the fact that most of these people are cured and survive with the advent of modern medicine, infertility is related to serious psychological and relationship implications and parenthood is a significant issue for those patients. Semen cryopreservation option is available for postpubertal adolescent and adult men, while children do not have this storing option since they do not have mature spermatozoa. However, their testes contain spermatogonial stem cells (SSCs), which are initiators of spermatogenesis. Promising findings in animal studies and human cell lines have encouraged scientists that SSCs may be hope for restoring fertility option of patients who cannot produce functional sperm and who have no other choice to preserve their future fertility. For this reason, several centers around the world already began to collect and cryopreserve testicular tissue or cells with anticipation that SSC-based therapies will be available in the near future; however, an optimal transplantation design in humans is yet to be developed. Here we propose an allogeneic testicular stem cell transplantation with an encapsulation device to restore fertility in patients with infertility. We endeavor to discuss the reliability of this method with the current literature and bring the evidence on its feasibility.