Development of an in vivo experimental system for spermatogenesis by ectopic grafting of marmoset testis tissue into immunodeficient mice

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Background: Ectopic grafting of testicular tissue into immunodeficient mice is a new experimental system that can be used not only to study spermatogenesis but also to preserve male gonadal function. This technique has been used recently to differentiate the neonatal testes of different species up to the level of complete spermatogenesis, however, spermatogenesis in testicular graft from common marmoset (Callithrix jacchus) does not proceed beyond the spermatogonial stage. In this study we examined spermatogenic recovery of immature marmoset testis in ectopic grafts using NOG mice (NOD/SCID/γcnull) as recipients, which are known as an excellent animal models for engraftment of human normal cells. Methods: Male castrated NOG mice received five or eight testicular grafts from newborn (0 day old) and infant (7 months old) marmosets. Two to seven months later, grafts were removed from the recipients and their numbers, size, and histology were examined. Results and discussion: Graft survival rate was 87%(13/15) for the newborn and 75%(24/32) for the infant. Testicular tissues from a newborn marmoset developed up to the stage of differentiated spermatogonia (A type and B type) with a small amount of early spermatocytes in seven months, whereas they mainly contained immature spermatogonia (gonocytes) before grafting. The level of spermatogenesis in grafts from newborn testis was comparable to, or more advanced than, that in the control testis in vivo. On the other hand, spermatogenesis recovery was limited in infant marmosets, arresting the germ cells probably at the stage of secondary spermatocytes, while spermatids were observed in age-matched control testis. Complete spermatogenesis in testicular grafts from marmosets did not succeed, however, recovery rate and graft development in the present study were superior to those reported by other authors. Using NOG mice as recipients might improve graft survival and conditioning of testicular development in ectopic grafting.