Biomedical Engineering Reference
In-Depth Information
Several strategies for protection of spermatogonial cells could be developed for
application in a clinical setting [for review see Jahnukainen et al. (
2006b
) and Schlatt
et al
.
(
2009
)]. While cryopreservation of sperm offers a standardized and routine
option for fertility preservation in adult patients, prepubertal children cannot donate
sperm for cryostorage. Moreover, cryopreservation of sperm represents a finite
source of gametes. Several alternatives have been discussed based on the high regen-
erative potential of the seminiferous epithelium that is supported by spermatogonial
stem cells. Although the somatic environment can also be affected by irradiation and
toxic exposures, this appears to be more resistant than germ cells (Bar-Shira
Maymon et al. 2004; Zhang et al.
2008
). Autologous transplantation of spermatogo-
nial stem cells, presented in Chap. 11 of this topic, represents an option for fertility
preservation in young patients. Other alternatives are the xenografting of testicular
tissue and cells into immunodeficient mice. Especially prior to puberty, when the
testis consists of cords and the only germ cells are spermatogonia, the developing
testis appears to be tolerant to hypoxia and temporary insufficient blood supply
rendering it liable to manipulation of cells and tissue that maintain their full devel-
opmental potential. This creates a very promising scenario for ectopic or orthotopic
testicular (auto or xeno)-grafting of immature testis tissue fragments and cells.
Besides preservation of fertility, xenotransplantation of testicular tissue and cells
open new avenues for experimental investigation in a way that was not possible
before or logistically very difficult; a small number of donors is needed to perform
valid comparative studies. Instead of exposing groups of males to different gonado-
toxic strategies, groups of mice carrying xenografts from few juvenile donors are
exposed to such treatments. Grafts can be collected then at different points for
subsequent analysis. This chapter focuses on testicular grafting and summarizes
primarily the advances achieved in non-human primates and humans with respect to
the application of testicular grafting for research and fertility protection.
10.2
Testicular Tissue Grafting: A Comparative Overview
Grafting of any tissue can be considered a specialized form of organ “culture.” The
host serves as a living bioincubator. Not only is the environment well controlled
but also the blood supply to the grafted tissue is restored. At first glance, the testis
does not appear to be a suitable tissue for grafting because of the complexity of
the seminiferous epithelium and the architecture of its vascular and duct systems.
However, several reports on testicular transplantation of the organ as a whole or of
testicular tissue were published in the 1920s and have been reviewed by Gosden
and Aubard (
1996a, b
). These studies were performed in a variety of species but
most of these experiments were performed in sheep, rats, and guinea pigs. They
have provided important insights into testicular function, especially on Leydig
cells and effects of temperature on spermatogenesis. An important breakthrough for
grafting came through the availability of immunodeficient recipient mice. They
allow xenotransplantation of testicular and other tissues (Paris et al.
2004
) without
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