Gene therapy for non-obstructive azoospermia: therapeutic avenues and translational pathway to clinical application

Non-obstructive azoospermia (NOA) represents the most severe male infertility. Although microsurgical testicular sperm extraction combined with intracytoplasmic sperm injection offers opportunities, approximately 50% of NOA patients still fail to obtain sperm for clinical treatments. Fortunately, the emergence of precision medicine, particularly advances in gene therapy, has opened new therapeutic avenues for NOA in preclinical studies, demonstrating proof-of-concept in animal models. This review examines current progress in NOA gene therapy. Firstly, three principal therapeutic strategies: lipid nanoparticle-mediated mRNA delivery for transient protein replacement, CRISPR-based gene editing for permanent correction, and stem cell-based approaches combined with genetic modification are comparatively analyzed. Subsequently, particular emphasis is placed on recent breakthroughs in testicular mRNA delivery that have successfully restored spermatogenesis in NOA mouse models, resulting in viable offspring. Furthermore, the delivery technologies including adeno-associated viral vectors, and non-viral methods are critically evaluated to assess their respective advantages, limitations, and suitability for different testicular cell types. The review also addresses critical safety considerations, such as off-target effects, germline transmission risks, and epigenetic consequences. Finally, we discuss the translational roadmap toward clinical application, and how the obstacles including delivery optimization, long-term safety validation, and the regulatory pathways to affect the transition from preclinical proof-of-concept to first-in-human trials.