Maturation of human cumulus-free germinal vesicle-stage oocytes to metaphase II by coculture with monolayer Vero cells.

The objective of this study was to evaluate and compare the efficacy of coculture with Vero cells (monkey kidney cells) and in-vitro culture in B2 Ménézo medium for the maturation of germinal vesicle (GV)-stage cumulus-free human oocytes to metaphase II. Cumulus-free human GV-stage oocytes obtained after ovulation induction and retrieval via vaginal ultrasound echo-guided puncture were put either in coculture with Vero cells or in 25 microliters droplets of B2 Ménézo medium. In a controlled randomized study, 145 GV-stage oocytes were matured in vitro: 72 were placed in the coculture system with Vero cells and 73 were cultured in B2 alone. After 30 h of in-vitro culture, 82.4% had dissolved the nuclear membrane and extruded the first polar body in the coculture system compared with 37% in B2 medium (P < 0.001). A significant difference was also noticed in the number of GV-stage oocytes which underwent GV breakdown; the proportion of oocytes which did not extrude the first polar body (metaphase I) was 1.6% in the coculture system compared to 44.0% in the B2 medium. It can be concluded that coculture with Vero cells improves the in-vitro maturation of cumulus-free human GV-stage oocytes.