Modular mRNA lipid nanoparticle platform rescues diverse genetic male infertility

Genetic male infertility arises from diverse mutations that disrupt spermatogenesis, yet molecular therapies capable of restoring germ-cell function remain limited. Messenger RNA (mRNA) therapeutics offer transient protein replacement without permanent genome modification, but efficient and safe delivery to the seminiferous epithelium remains challenging. Here we develop a modular mRNA-lipid nanoparticle (LNP) platform that restores spermatogenesis across multiple genetic infertility models. Systematic comparison of clinically relevant ionizable lipids revealed that the clinically validated ionizable lipid MC3 uniquely provides sustained mRNA expression in the seminiferous epithelium while minimizing inflammation and systemic leakage. In contrast, lipids such as ALC-0315 produced higher transient reporter expression but failed to support functional rescue. A single intratesticular injection of an optimized Papolb mRNA restored spermiogenesis in [~]25% of seminiferous tubules and generated functional sperm capable of producing healthy offspring through intracytoplasmic sperm injection. The platform extended to both meiotic (Spo11) and post-meiotic (Btbd18) arrest models and enabled efficient mRNA expression in cultured human seminiferous tubules. Comprehensive analyses demonstrated long-term safety in treated animals and multigenerational genetic and epigenetic stability in offspring. Together, these findings establish a modular mRNA-LNP platform for correcting diverse genetic causes of male infertility and reveal a design principle for extrahepatic RNA delivery: delivery efficiency alone does not predict functional therapeutic rescue, highlighting the importance of expression kinetics and tissue context in nanoparticle design.