Development of operational immunologic tolerance with neonatal gene transfer in nonhuman primates: preliminary studies

Abstract

Achieving persistent expression is a prerequisite for effective genetic therapies for inherited disorders. These proof-of-concept studies focused on AAV administration to newborn monkeys. Serotype rh10 AAV expressing ovalbumin and green fluorescent protein (GFP) was administered intravenously at birth and compared to vehicle controls. At 4 months postnatal age a second injection was administered intramuscularly, followed by vaccination at 1 year of age with ovalbumin and GFP. Ovalbumin was highest 2 weeks post-administration in the treated monkey, which declined but remained detectable thereafter; controls demonstrated no expression. Long-term AAV genome copies were present in myocytes. At 4 weeks, neutralizing antibodies to rh10 were present in the experimental animal only. With AAV9 administration at 4 months, controls showed transient ovalbumin expression that disappeared with development of strong anti-ovalbumin and anti-GFP antibodies. In contrast, increased and maintained ovalbumin expression was noted in the monkey administered AAV at birth, without antibody development. After vaccination, the experimental monkey maintained levels of ovalbumin without antibodies, whereas controls demonstrated high levels of antibodies. These preliminary studies suggest that newborn AAV administration expressing secreted and intracellular xenogenic proteins may result in persistent expression in muscle, and subsequent vector administration can result in augmented expression without humoral immune responses.

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

“…[30][31][32][33] Other studies that have focused on gene transfer in fetuses and newborns have shown longterm gene expression in muscles or the heart for several years without any evidence of adverse findings. [34][35][36][37][38] By contrast, when AAV vectors are administered to the liver of newborns, transgene expression can be significantly reduced over time, 39 making liver-directed gene therapy potentially challenging for the treatment of pediatric diseases. In this study, CNS and PNS vector ge- % neurons = mean percentage of hIDUA-positive neurons over total number of same-type neurons in frontal cortex pyramidal cells (15 fields); the hippocampus CA2-CA3 region (5 fields); the Purkinje cell layer of cerebellum (5 fields); the anterior horns of spinal cord sections (1 section per segment); and the DRG (up to 4 DRG per segment).…”

Fetal gene therapy for neurodegenerative disease of infants

“…The presence of GCase in the skin of the knockout nGD mice precluded us from investigating this specifically. Nevertheless, immune tolerance towards a non-mammalian protein following fetal or neonatal gene delivery has been observed in non-human primate studies 25 and in mice this allowed effective re-administration of vector 26. Avoidance of an immune response following gene therapy is important.…”

Dosing and Re-Administration of Lentiviral Vector for In Vivo Gene Therapy in Rhesus Monkeys and ADA-Deficient Mice

“…In single-exposure studies with unmodified ADA LV, neither immune-deficient Ada −/− mice nor immune competent Ada +/− mice treated as neonates had no or little anti-vector IgG response. This finding is more likely related to the tolerizing effect of neonatal exposure to vector, as has been demonstrated in studies with adeno-associated viral vectors (AAV) 24, 25, 26. In Ada −/− mice treated at 4 months of age (after 4 months of ERT), the concentration of anti-vector antibody increased 15,000- to 20,000-fold, a magnitude of increase not observed in immune-competent Ada +/− mice treated as adults.…”