Review of injection techniques for spermatogonial stem cell transplantation

BACKGROUND

Although the prognosis of childhood cancer survivors has increased dramatically during recent years, chemotherapy and radiation treatments for cancer and other conditions may lead to permanent infertility in prepubertal boys. Recent developments have shown that spermatogonial stem cell (SSC) transplantation may be a hope for restoring fertility in adult survivors of childhood cancers. For this reason, several centres around the world are collecting and cryopreserving testicular tissue or cells anticipating that, in the near future, some patients will return for SSC transplantation. This review summarizes the current knowledge and utility of SSC transplantation techniques.

OBJECTIVE AND RATIONALE

The aim of this narrative review is to provide an overview of the currently used experimental injection techniques for SSC transplantation in animal and human testes. This is crucial in understanding and determining the role of the different techniques necessary for successful transplantation.

SEARCH METHODS

A comprehensive review of peer-reviewed publications on this topic was performed using the PubMed and Google Scholar databases. The search was limited to English language work and studies between 1994 (from the first study on SSC transplantation) and April 2019. Key search terms included mouse, rat, boar, ram, dog, sheep, goat, cattle, monkey, human, cadaver, testes, SSC transplantation, injection and technique.

OUTCOMES

This review provides an extensive clinical overview of the current research in the field of human SSC transplantation. Rete testis injection with ultrasonography guidance currently seems the most promising injection technique thus far; however, the ability to draw clear conclusions is limited due to long ischemia time of cadaver testis, the relatively decreased volume of the testis, the diminishing size of seminiferous tubules, a lack of intratesticular pressure and leakage into the interstitium during the injection on human cadaver testis. Current evidence does not support improved outcomes from multiple infusions through the rete testes. Overall, further optimization is required to increase the efficiency and safety of the infusion method.

WIDER IMPLICATIONS

Identifying a favourable injection method for SSC transplantation will provide insight into the mechanisms of successful assisted human reproduction. Future research could focus on reducing leakage and establishing the optimal infusion cell concentrations and pressure.

Three-dimensional structure of seminiferous tubules in the adult mouse

Seminiferous tubules develop from sex cords, which are embryonic structures with simple C-shaped arches. Histologically, the epithelium of adult mouse seminiferous tubules has been divided into 12 stages based on the associations of spermatogenic cells in four cycles of spermatogenesis. However, the gross characteristics of the seminiferous tubules themselves, including their number, length, run, and mutual relationships remain largely unknown. In the present study, we analyzed all seminiferous tubules in a single adult mouse testis with high resolution using serial paraffin sections and high-perfomance three-dimensional reconstruction software. There were 11 seminiferous tubules with an average length of 140 mm. Each tubule ran along circular paths within the testis while making convolutions with cranial and caudal hairpin turns. The cranial turns of all tubules were in contact with the tunica albuginea, whereas the caudal turns were not, resulting in funnel-shaped networks of these tubules with tapered caudal portions. The caudally located networks surrounded the preceding cranially located networks from the bottom and outside, similar to stacked paper cups. Five out of the 11 seminiferous tubules were continuous from one end to the other both connected with the rete testis (10 connection points). Nine branching points, one blind end, and 18 more connection points with the rete testis were detected in the remaining six seminiferous tubules, making the paths of these tubules complicated to various degrees. The present study revealed that the 3D structures of seminiferous tubules were highly regular as a whole in the adult mouse testis.