Human chorionic gonadotropin (hCG) has been considered as a primary target molecule for a contraceptive vaccine by the World Health Organization because of its physiological and temporal specificity. hCG is an essential factor for the successful implantation and establishment of early pregnancy. For a decade, the most advanced works in development of a contraceptive vaccine have been concentrated on polypeptide based vaccines targeted directly against hCG. Although many studies have reached the stage of clinical testing using a number of prototype vaccines based on different parts of hCG molecule, their efficacy has been disappointing (1-4).