Comparative analysis of immunocontraceptive vaccines in wild animals: Modes of action, molecular targets, and immunological responses.

Immunocontraceptive vaccines have emerged as a promising, non-invasive strategy for regulating fertility in wildlife, domestic animals, and humans, particularly in species such as elephants where conventional population control methods are often impractical or ethically challenging. These vaccines act by eliciting immune responses against critical reproductive targets, thereby disrupting gametogenesis, fertilization, or endocrine regulation. The major categories include gonadotropin-releasing hormone (GnRH)-based vaccines, zona pellucida (ZP)-based vaccines, and gamete-specific antigen vaccines. Anti-GnRH vaccines induce neutralizing antibodies that suppress the hypothalamic-pituitary-gonadal axis by inhibiting luteinizing hormone and follicle-stimulating hormone secretion, ultimately blocking steroidogenesis and gamete production. In contrast, ZP-based vaccines target oocyte surface glycoproteins, preventing sperm binding and fertilization. Emerging molecular targets, including sperm-egg interaction proteins such as IZUMO1 and JUNO, offer enhanced specificity. These vaccines predominantly stimulate humoral immune responses, with antigen-specific antibody production playing a central role, although cell-mediated immunity may contribute to sustained effects. In elephants, vaccines such as porcine zona pellucida (PZP) and GnRH-based formulations (e.g., GonaCon) have shown variable success in inducing reversible infertility, though challenges remain regarding booster requirements, duration of efficacy, and potential side effects. Advances in scientific technologies, particularly peptide engineering and viral-vector platforms, have contributed significantly to the development of immunocontraceptive vaccines by enhancing antigen specificity, immunogenicity, and overall vaccine performance. However, variability in immune responses, species-specific efficacy, and ethical considerations continue to limit widespread application. This review aims to help understanding the molecular and immunological mechanisms are essential for optimizing safe, effective, and sustainable fertility control strategies.