SURF1 (surfeit locus protein 1)-related Leigh syndrome is an early-onset neurodegenerative disorder, characterized by reduction in complex IV activity, resulting in disrupted mitochondrial function. Currently, there are no treatment options available. To test our hypothesis that adeno-associated viral vector serotype 9 (AAV9)/human SURF1 (hSURF1) gene replacement therapy can provide a potentially meaningful and long-term therapeutic benefit, we conducted preclinical efficacy studies using SURF1 knockout mice and safety evaluations with wild-type (WT) mice. Our data indicate that with a single intrathecal (i.t.) administration, our treatment partially and significantly rescued complex IV activity in all tissues tested, including liver, brain, and muscle. Accordingly, complex IV content (examined via MT-CO1 protein expression level) also increased with our treatment. In a separate group of mice, AAV9/hSURF1 mitigated the blood lactic acidosis induced by exhaustive exercise at 9 months post-dosing. A toxicity study in WT mice showed no adverse effects in either the in-life portion or after microscopic examination of major tissues up to a year following the same treatment regimen. Taken together, our data suggest a single dose, i.t. administration of AAV9/hSURF1 is safe and effective in improving biochemical abnormalities induced by SURF1 deficiency with potential applicability for SURF1-related Leigh syndrome patients.

The solute carrier family 6 member 1 ( SLC6A1 ) gene encodes the γ-aminobutyric acid (GABA) transporter GAT-1, the deficiency of which is associated with infantile encephalopathy with intellectual disability. We designed 2 AAV9 vectors, with either the JeT or MeP promoter, and conducted preclinical gene therapy studies using heterozygous and homozygous Slc6a1 -KO mice at different developmental ages and various routes of administration. Neonatal intracerebroventricular administration of either vector resulted in significantly normalized EEG patterns in Slc6a1 ^–/– or Slc6a1 ^+/– mice as well as improvement in several behavioral phenotypes of Slc6a1 ^–/– mice. However, some mortality and adverse effects were observed in neonatal-treated mice. Intrathecal administration of either vector at P5 normalized EEG patterns in Slc6a1 ^+/– mice, but in Slc6a1 ^–/– mice, the treatment only rescued nest building without impact on EEG. Both vectors were well tolerated in all mice treated at P5 or later (including WT mice), up to 1 year after injection. Overall, our data demonstrate compelling efficacy when mice are treated at an early development age. We also identified that outside of the neonatal treatment window, the severe homozygous KO model is more refractory to treatment, whereas our treatments in the heterozygous mice, which genotypically match human patients, have resulted in stronger benefits.

One method to target the central nervous system for treating neurological diseases involves utilizing the lumbar intrathecal route of administration. This approach bypasses the blood-brain barrier to directly access the cerebrospinal fluid and preferentially target cells within the central nervous system. Multiple published preclinical studies employing the lumbar intrathecal injection route have contributed to the development of gene therapy clinical trials; however, the described protocols are variable and dispersed across multiple resources. Here, a comprehensive set of protocols for lumbar intrathecal injections in neonatal, juvenile, and adult mice and rats for preclinical gene therapy studies is presented. With proper training, this injection technique can be performed quickly and reliably. In addition to detailing the injection protocol at each developmental stage, associated parameters, such as injection volume, that can influence study outcomes are discussed. To demonstrate the application of lumbar intrathecal injections for targeting the central nervous system, the expression of adeno-associated virus serotype 9 in the brain, spinal cord, and peripheral tissues is presented following a successful or unsuccessful injection.

Background/Objectives: Adeno-associated virus serotype 9 (AAV9) can cross the blood–brain barrier, making it widely used as a gene delivery vector for central nervous system (CNS) applications. Despite extensive use of AAV9 in translational research, variability in study designs makes cross-comparisons difficult to interpret. We designed a study in mice to generate a resource of AAV9 biodistribution across tissues for commonly used routes of administration and treatment ages. Methods: Lumbar intrathecal, intracerebroventricular, lumbar intrathecal and intracerebroventricular combination, or intravenous injections of vehicle or AAV9/GFP were performed in C57BL/6J male and female mice on postnatal day 1, 5, 10, or 28. Organs were collected at postnatal day 56 and biodistribution of AAV9/GFP was evaluated by quantifying GFP protein expression and vector genome copy number. Results: Direct cerebrospinal fluid injections led to higher transgene expression levels in the brain and spinal cord compared to intravenous administration but did not de-target transgene expression in peripheral tissues. Lumbar intrathecal and intracerebroventricular combination injections resulted in expression throughout the CNS but did not substantially increase expression in either the spinal cord or brain beyond the levels obtained with the respective single routes. Treatment age had effects on AAV9 biodistribution regardless of the route of administration, especially in the brain, eye, and liver. Conclusions: Our results provide the necessary biodistribution data to establish a standardized benchmark for comparison of the current gold standard AAV9 to next generation viral vectors. Additionally, this body of work can provide valuable insights for the design of translational gene therapy studies.

One method to target the central nervous system for treating neurological diseases involves utilizing the lumbar intrathecal route of administration. This approach bypasses the blood-brain barrier to directly access the cerebrospinal fluid and preferentially target cells within the central nervous system. Multiple published preclinical studies employing the lumbar intrathecal injection route have contributed to the development of gene therapy clinical trials; however, the described protocols are variable and dispersed across multiple resources. Here, a comprehensive set of protocols for lumbar intrathecal injections in neonatal, juvenile, and adult mice and rats for preclinical gene therapy studies is presented. With proper training, this injection technique can be performed quickly and reliably. In addition to detailing the injection protocol at each developmental stage, associated parameters, such as injection volume, that can influence study outcomes are discussed. To demonstrate the application of lumbar intrathecal injections for targeting the central nervous system, the expression of adeno-associated virus serotype 9 in the brain, spinal cord, and peripheral tissues is presented following a successful or unsuccessful injection.