Zona pellucida glycoproteins based immunocontraceptive vaccines: strategies for development and their applications

The mammalian oocyte is surrounded by an extra-cellular matrix, the zona pellucida (ZP), composed of three major glycoproteins (ZP1, ZP2 and ZP3). The ZP glycoproteins, by virtue of their tissue specificity and critical role during mammalian fertilization, have emerged as potential candidate antigens for the development of an immunocontraceptive vaccine. Molecular characterization of ZP glycoproteins from several species, reveals a variable degree of homology among the deduced primary amino acid sequences, which provided an opportunity to undertake active immunization studies in heterologous animal models. Active immunization of various animal species with either native ZP glycoproteins or those obtained by recombinant DNA technology led to the inhibition of fertility. Thus ZP glycoproteins based immunocontraceptive vaccines offer an attractive proposition for controlling wild life population. To make it a practical proposition, additional research inputs are required to optimize and devise novel strategies for vaccine delivery. Observed ovarian dysfunction, often associated with immunization by ZP glycoproteins is one of the major stumbling blocks for their use in humans. Ongoing studies to delineate appropriate B cell epitopes of ZP glycoproteins that are devoid of oophoritogenic T-cell epitopes, which will inhibit fertility without concomitant oophoritis, will be critical to determine their feasibility for human use.