Biomedical Engineering Reference
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Busulfan doses that cause long-term infertility (e.g., 8-12 mg/kg) also cause
severe hematopoietic deficits in some animals, sometimes with life-threatening
and mortal consequences (Hermann et al.
2007
). While the data also indicate that
these negative side-effects are variable, prophylactic treatments (e.g., antibiotic
regimen, blood transfusions) concurrent with and following busulfan treatment,
along with peripheral blood mononuclear cell (PBMC) transplantation to restore
the hematopoietic system, help to maintain animal health (Hermann and Orwig,
unpublished).
11.3.6
Testicular Irradiation
Testicular irradiation is another approach that depletes the seminiferous epithelium
of primate testes and may generate a suitable environment for SSC transplantation.
In rhesus macaques, numbers of A
dark
, A
pale
, and B spermatogonia decline acutely to
less than 5% of starting numbers in the first several weeks after low doses of radia-
tion (1-4 Gy) (van Alphen et al.
1988
). However, spermatogonial numbers return
to 70% of pretreatment levels over the course of several months to a year after treat-
ment with low-dose radiation (1-2 Gy) (van Alphen and de Rooij
1986
). Thus,
similar to results of 4 mg/kg busulfan treatment (see Fig.
11.2
), low doses of tes-
ticular irradiation do not permanently ablate primate SSCs, and may not be suitable
for testing the regenerative capacity of transplanted stem cells due to competition
with remaining SSCs. In the prepubertal rhesus testis, radiation doses greater than
6 Gy are required for permanent depletion of germ cells, although the effect is
heterogeneous between animals (de Rooij et al.
2002
). High-dose irradiation
(10 Gy) of immature rhesus monkeys led to a failure to achieve a pubertal increase
in testis volume, although spermatogenesis was observed in one animal (Schlatt
et al.
2009
). While local irradiation to the testis avoids the potentially lethal side-
effects observed with whole-animal chemotherapy treatments, evidence from rats
suggests that radiation may damage the testicular somatic environment, leading to
reduced ability of transplanted SSCs to engraft and produce spermatogenesis
[(Zhang et al.
2006b
); see Chap. 9]. Additional studies are needed to determine
whether this complication is unique to the rat or extends to other species. In the end,
radiation and chemotherapy may prove to be complimentary approaches to gener-
ate recipient animals with testes devoid of endogenous spermatogenesis suitable for
SSC transplantation studies.
11.3.7
Ultrasound-Guided Rete Testis Injection
Ultimately, autologous SSC transplantation in primates is the only way to test the full
regenerative potential of primate SSCs and evaluate the interaction between SSCs and
their true niches located in seminiferous tubules. In rodents, the rete testis is readily
visible on the surface of the testis and the efferent duct bundle can be cannulated
to allow retrograde injection into recipient seminiferous tubules (Ogawa et al.
1997
).
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