Adult Stem Cells in the Human Testis

Ellen Goossens, PhD, MSc; Herman Tournaye, MD, PhD, MSc

Disclosures

Semin Reprod Med. 2013;31(1):39-48. 

In This Article

Cell Therapy

Regenerative Medicine

Methods for stem cell therapy based on ESC or induced pluripotent stem cells have important disadvantages because of their tumorigenesis or ethical controversies. Transdifferentiation from (autologous) adult stem cells could be a more feasible and easier method. Moreover, compared with ESC-based research, there are fewer ethical constraints. SSCs share many molecular characteristics with ESC, providing new and unique opportunities for the therapeutic use of SSCs for regenerative medicine. The banking and transplantation of human SSCs may become a clinical routine for the preservation of male fertility in the future, so there could be a clinical future for SSC-based therapies as well.

Studies in mice showed the potential of SSCs to generate tissues of all three germ layers (functional neurons, glia, cardiomyocytes, and other somatic cell types) without first converting into a less differentiated state.[126–129] Our research group was able to transdifferentiate SSCs into hematopoietic cells in vivo. The donor-derived cells presented phenotypical and functional characteristics of hematopoietic cells in vitro and in vivo.[130] However, the mechanism of transdifferentiation is still unclear. Some researchers believe in cell reprogramming.[131,132] Others suggest that SSCs first become pluripotent before differentiating into another cell type.[133] It is possible that a certain subpopulation of SSCs is pluripotent (Pou5f1+/C-kit+), whereas the Pou5f1+/C-kit SSCs are committed to the germ line. The pluripotent SSCs may transdifferentiate when exposed to a different microenvironment.[134]

Transgenerational Therapy

Spermatogonial stem cells are the only stem cells in humans that can transmit parental genetic information to the offspring, making them an attractive target cell population for transgenerational gene therapy. Mouse SSCs have been successfully transfected with the use of a retroviral vector. The co-injection of retroviral particles and germ cells into recipient testes also results in incorporation of the reporter gene. It is now possible to transfect both adult and immature stem cells by retroviral-mediated gene delivery in vitro[135] and in vivo by using a retrovirus vector.[136]

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