Development of antral follicles after xenografting of isolated small human preantral follicles

Small human pre-antral follicles can be enzymatically isolated from the surrounding stroma, and are able to survive after 7 days of xenografting. The aim of the present study was to assess the developmental capacity of enzymatically isolated human follicles after long-term xenografting to severe combined immunodeficient (SCID) mice. Ovarian biopsies were obtained from three women 26-29 years of age. Human ovarian tissue was enzymatically dissociated using collagenase or a purified collagenase blend to obtain isolated follicles that were xenografted to SCID mice for 5 months. Recombinant FSH was given to the mice for the last 2 weeks. Five months after xenografting, follicular morphology was assessed by histology, and follicular proliferation by Ki-67 immunohistochemistry. Four grafts containing a total of 84 follicles were recovered. This follicular population was composed of 11 primordial follicles, 38 primary follicles, 31 secondary follicles and four antral follicles. Ki-67 was found to stain granulosa cells in antral follicles intensively. The results demonstrate, for the first time, that isolated human follicles are able to survive after long-term xenografting, and can develop into antral follicles after FSH stimulation.