Novel immunocontraceptive targets in mammals: uterine secretions and the conceptus; a marsupial approach

We report the first immunocontraceptive trial in mammals using a uterine-secreted protein, the marsupial shell coat protein 4 (CP4). The marsupial shell coat, which surrounds the conceptus for 60-80 % of gestation, is secreted by the uterine epithelium. Following immunization against GST-CP4, the fertility of female common brushtail possums (n = 6) was significantly reduced (P = 0.000), and this reduction in fertility was positively correlated with the maximum GST-CP4 humoral immune response (P = 0.025). Ultrastructural examination of the reproductive tract indicated that the cellmediated immune response against GST-CP4 targeted the shell coat, the shell-free conceptus and the uterine glandular epithelium, thus preventing normal conceptus development and uterine secretion of shell coat proteins and nutrients. These results show that uterine-secreted proteins are promising immunocontraceptive targets, especially in pest mammal species, e.g. possum, rabbit and horse, that have uterine-secreted additions to embryonic coats, or that have late implantation requiring uterine nutrient provisioning from secretions.