Male germ cell transplantation: present achievements and future prospects.

Germ cells are unique, since their surviving descendants can undergo meiosis and differentiate into gametes, which transmit genetic material from one generation to another. We now know that male germ cells, whether they be primordial germ cells in gonadal ridges, gonocytes, or stem spermatogonia, are transplantable. The donor cells can be transferred by direct microinjection into the seminiferous tubules, rete testis or efferent ducts, depending on the recipient species. Following transplantation, the donor cells undergo spermatogenesis in the host's seminiferous tubules in rats and mice, and have even sired offspring in mice. Interspecific germ cell transfer is possible if the recipient's immune system is defective; nude or SCID mice can even produce rat spermatozoa. However, the major obstacle restricting widespread use of this new technology is its extremely low success rate. This article discusses some ideas for improving the success rate of the transfer technique, and considers several potential applications.