Long‐Term Safety and Efficacy of AAV9 Vectors Expressing Human SMN1 Gene: A Preclinical Study

Spinal muscular atrophy (SMA) is a severe genetic neuromuscular disorder caused by deletions or mutations in the SMN1 gene, leading to reduced levels of the survival motor neuron (SMN) protein. Gene therapy using adeno-associated virus serotype 9 (AAV9) has emerged as a promising treatment strategy for SMA by enabling systemic delivery of a functional SMN1 gene. This preclinical study evaluates the long-term safety and efficacy of an AAV9 vector expressing a codon-optimized human SMN1 gene (AAV9-hcoSMN) in neonatal mice. A single intravenous dose of 5 × 10¹¹ vector genomes per mouse was administered, with animals monitored over a 24-week period for therapeutic outcomes and safety profiles. Safety assessments, including clinical observations, haematological and biochemical analyses (such as CBC, liver function tests and coagulation tests), necropsy and histopathological examinations via H&E, revealed no significant adverse effects. Treated mice demonstrated 100% survival rates and exhibited no abnormalities in organ structure or function compared to controls. Efficacy assessments using quantitative PCR confirmed robust SMN1 transgene expression in key tissues, including the central nervous system, heart, liver and skeletal muscles. These findings demonstrate that AAV9-hcoSMN therapy achieves sustained and widespread transgene expression with no observable toxicity in a neonatal mouse model, reinforcing the therapeutic potential of AAV9-based gene delivery for SMA. By providing robust preclinical evidence of both safety and efficacy, this study contributes to the growing body of data supporting gene therapy as a viable, long-term treatment strategy for SMA. These results also help inform vector design, dosing strategies and safety monitoring for future clinical translation. Further studies in larger animal models are warranted to assess long-term durability and immunogenicity prior to human application. SUMMARY: Spinal muscular atrophy (SMA) is a serious genetic disorder that weakens muscles and can be life-threatening. Our study tested a potential gene therapy using a harmless virus (AAV9) to deliver a healthy version of the faulty gene that causes SMA. We treated newborn mice and observed them for 6 months to check for any side effects and see if the therapy worked. The results were promising-treated mice had no health problems, and the new gene was active in important organs like the brain, muscles, and heart. This research brings us closer to a safe and effective treatment for SMA.