Safe and Sustained Expression of Human Iduronidase After Intrathecal Administration of Adeno-Associated Virus Serotype 9 in Infant Rhesus Monkeys

Abstract

Many neuropathic diseases cause early, irreversible neurologic deterioration, which warrants therapeutic intervention during the first months of life. In the case of mucopolysaccharidosis type I, a recessive lysosomal storage disorder that results from a deficiency of the lysosomal enzyme a-l-iduronidase (IDUA), one of the most promising treatment approaches is to restore enzyme expression through gene therapy. Specifically, administering pantropic adeno-associated virus (AAV) encoding IDUA into the cerebrospinal fluid (CSF) via suboccipital administration has demonstrated remarkable efficacy in large animals. Preclinical safety studies conducted in adult nonhuman primates supported a positive risk-benefit profile of the procedure while highlighting potential subclinical toxicity to primary sensory neurons located in the dorsal root ganglia (DRG). This study investigated the long-term performance of intrathecal cervical AAV serotype 9 gene transfer of human IDUA administered to 1-month-old rhesus monkeys (N = 4) with half of the animals tolerized to the human transgene at birth via systemic administration of an AAV serotype 8 vector expressing human IDUA from the liver. Sustained expression of the transgene for almost 4 years is reported in all animals. Transduced cells were primarily pyramidal neurons in the cortex and hippocampus, Purkinje cells in the cerebellum, lower motor neurons, and DRG neurons. Both tolerized and non-tolerized animals were robust and maintained transgene expression as measured by immunohistochemical analysis of brain tissue. However, the presence of antibodies in the non-tolerized animals led to a loss of measurable levels of secreted enzyme in the CSF. These results support the safety and efficiency of treating neonatal rhesus monkeys with AAV serotype 9 gene therapy delivered into the CSF.

Adeno-Associated Virus-Induced Dorsal Root Ganglion Pathology

“…This result occurred despite good transgene expression levels when the animals were necropsied almost 4 years post-injection. 11 This observation may suggest a more favorable safety profile when dosing infants or that acute pathology does not progress and in fact resolves; we did not have any early time-point necropsies in this study.…”

“…The four animals treated as infants showed no signs of DRG or SC pathology as previously reported. 11 This result needs to be interpreted with caution due to the small sample size and a possible effect of the study endpoint (4 years post-injection was much later than any time point involving juvenile or adult animals). In addition, and importantly, sex had no effect on SC or DRG pathology (Fig.…”

Blood-Brain Barrier and Delivery of Protein and Gene Therapeutics to Brain

“…The ADA titer included neutralizing antibodies (NAb) against NAGLU, and these NAb's caused a depletion of endogenous NAGLU in the normal primates (Murrey et al, 2014). A similar immune response against the transgene product was observed in infant Rhesus monkeys administered AAV encoding the lysosomal enzyme, iduronidase (IDUA), via an occipital intrathecal injection (Hordeaux et al, 2019). An immune response against the therapeutic protein could ultimately negate the therapeutic effect of the AAV gene therapy.…”

“…While lentiviral gene therapy is permanent, is it difficult to see how an episomal form of gene therapy, such as with AAV, can be life-long, unless the AAV permanently integrates into the host genome. Expression of the AAV genome in primates for as long as 4 years have been observed (Hordeaux et al, 2019).…”

Long-Term Delivery of an Anti-SIV Monoclonal Antibody With AAV

“…Both of these reports used periodic induction of expression of an erythropoietin identical in sequence to the monkey's own erythropoietin over 5 or more years of study. Additional examples include the persistent expression of dopamine-synthesizing enzymes in the putamen reported in one monkey for 15 years in a primate model of Parkinson's disease (54); the sustained expression of human α-L-iduronidase, an important enzyme required for the lysosomal degradation of glycosaminoglycans, reported for almost 4 years after intrathecal cervical AAV9 gene delivery in four one-month-old rhesus monkeys (55); the sustained expression of alpha-1 antitrypsin for over 5 years after one AAV vector administration in alpha-1 antitrypsin deficient patients (56); and the successful expression for 3.5 years obtained in two dogs of a dystrophin gene in a canine model for human Duchenne muscular dystrophy using AAV6 and a brief course of immunosuppressants (57), or in a similar study for over 2 years in two dogs using AAV8 in the absence of immunosuppression (58). Remarkably our animal 84-05 never received any immunosuppressant.…”