Immunization with Recombinant Murine Cytomegalovirus Expressing Murine Zona Pellucida 3 Causes Permanent Infertility in BALB/c Mice Due to Follicle Depletion and Ovulation Failure

Abstract

Zona pellucida (ZP) glycoproteins are promising candidate antigens for use in immunocontraceptive vaccines because of their crucial role in mammalian fertilization. A single intraperitoneal immunization with recombinant murine cytomegalovirus engineered to express murine ZP3 (rMCMV-mZP3) induces permanent infertility with no evident systemic illness in female BALB/c mice. To investigate the mechanisms underpinning reproductive failure elicited by rMCMV-mZP3, ovarian parameters and reproductive function were evaluated at time points spanning 10 days to 5 wk after virus inoculation. Fertility was substantially impaired by 14 days after inoculation with rMCMV-mZP3 and was fully ablated by 21 days. Pregnancies established after inoculation but before complete infertility showed no adverse effects on fetal viability assessed at Day 17.5 post coitum (pc). Infertile mice retained estrous cycling activity and remained receptive to mating; however, at Day 3.5 pc there were fewer developing embryos and corpora lutea, plasma progesterone content was reduced, and there was no evidence of excess unfertilized oocytes. Consistent with this, profound ovarian pathology was evident from 10 days after rMCMV-mZP3 inoculation, with a decline first in mature ovarian follicles and then in immature ovarian follicles and with diminished expression of genes regulating follicle development, including Nobox, Gdf9, and Gja1 (connexin43). Follicle loss was associated with mild focal oophoritis and with recruitment of inflammatory leukocytes, predominantly CD4+ and CD8+ T cells evident from 10 days after virus inoculation. These data indicate that vaccination with rMCMV-mZP3 causes permanent infertility in BALB/c mice principally due to induction of ovarian autoimmune pathology leading to progressive oocyte depletion and eventual ovulation failure..