**4. Conclusion**

Among the different models used in *in vitro* spermatogenesis better results have been achieved through 3D culture systems. Formation of EBs using germ and Sertoli cells seems to be more efficient and resemble the testicular niche environment compared to soft agar culture system. Although this system is well supported for the proliferation and differentiation of putative germ cells obtained from somatic stem cells up to the spermatids state there is no firm evidence to conclude the support for an efficient spermiogenesis process. Complete spermatogenesis has been achieved by transplanting stem cells or putative germ cells into testes in few studies, but with lower efficiency. Clinical applications of xeno or autologous transplantation studies among humans, and between humans and animals are still far away due to ethical and safety related issues. Similarly, use of autologous stem cells for differentiation of germ cells and infertility treatment may have little value for the patients with cancer or genetic diseases, as there is a possibility to re-infuse cancer cells or passing genetic abnormalities to offspring. However, *in vitro* maturation of germ cells may be immensely helpful for men with maturation arrest or azoospermia due to non-genetic causes.
