Improved retroviral vector design results in sustained expression after adult gene therapy in mucopolysaccharidosis I mice

Abstract

Background Mucopolysaccharidosis I (MPS I) is a lysosomal storage disease due to α-L-iduronidase (IDUA) deficiency that results in the accumulation of glycosaminoglycans (GAG). Gene therapy can reduce most clinical manifestations, but mice that receive transfer as adults lose expression unless they receive immunosuppression. Increasing liver specificity of transgene expression has reduced immune responses to other genes. Methods A gamma retroviral vector was generated with a liver-specific human α1-antitrypsin promoter and the canine IDUA cDNA inverted relative to the retroviral long-terminal repeat. Adult MPS I mice received the vector intravenously at 6 weeks of age and were assessed for expression via serial serum IDUA assays. Functional testing and organ analysis were performed at 8 months. Results This vector resulted in high specificity of expression in liver, and serum IDUA activity was stable in 90% of animals. Although the average serum IDUA activity was relatively low at 12.6 ± 8.1 units/mL in mice with stable expression, a relatively high percentage of enzyme contained the mannose 6-phosphorylation necessary for uptake by other cells. At 6.5 months after transduction, most organs had high IDUA activity and normalized GAG levels. There was complete correction of hearing and vision abnormalities and significant improvements in bone, although the aorta was refractory to treatment. Conclusions Stable expression of IDUA in adult MPS I mice can be achieved without immunosuppression by modifying the vector to reduce expression in the spleen. This approach may be effective in patients with MPS I or other lysosomal storage diseases.

Therapies for the bone in mucopolysaccharidoses

“…Adult MPS I mice treated with the γ-retroviral vector intravenously resulted in relative low IDUA activity, although a complete correction of hearing and vision abnormalities, and partial correction in femur diameters and bone mineral density was observed [120,121]. Neonatal treatment of MPS I dogs led to an increase in serum IDUA activity that was up to 28-fold greater than wild-type levels and was maintained for 1.8 years [119].…”

“…After two years of follow-up of treated dogs, skeletal disease evaluation showed no improvement in lengths of cervical or lumbar vertebral bodies, reduction of vertebral fusion, modest improvement in widening, beaking, and tipping in cervical spine, reduction in vertebral space, and reduction in severity of stifle joint effusions. In summary, neonatal gene therapy in MPS I dogs ameliorates, but does not prevent, skeletal disease even with supraphysiological enzyme activity levels in serum and several organs [120,121]. …”

“…Gene therapy reports for MPS VII have used plasmid [132] sleeping beauty transposon [117], gamma-retroviral [120,121,132,133], lentiviral [134], and AAV [135,136] vectors. Favorable results for bone lesions were reported in MPS VII dogs by neonatal gene therapy using a gamma-retroviral vector [133].…”

Therapies of mucopolysaccharidosis IVA (Morquio A syndrome)

“…GAG and secondarily elevated enzymes (β-hexosaminidase and β-glucuronidase) were reduced in most tissues, leading to the correction of hernias, chest deformities, joint disease, facial dysmorphia, corneal clouding, valvular heart disease and aortic dilatation. However, lesions in aorta and cervical spine were more difficult to correct, even when animals were treated in the neonatal period and with supraphysiological enzyme levels that were maintained for long periods (up to 7 years) [62,63]. Self-inactivating (SIN) retroviral vectors have also been evaluated to reduce the insertional mutagenesis associated with γ-retroviral vectors.…”

Liver-Directed Human Amniotic Epithelial Cell Transplantation Improves Systemic Disease Phenotype in Hurler Syndrome Mouse Model

“…Gene therapy and hematopoietic stem cell (HSC)‐based therapy have been proposed as potential new therapies. At the preclinical stage, intravenous delivery of viral vectors and gene therapy approaches have shown promise, but the residual disease still affects nervous, skeletal, and heart tissue of these same mice in adulthood 6, 7. While HSC therapies have shown therapeutic effects on visceral organs of MPS1 mice, they do not adequately correct 8, or show only partial benefit to the neurological disease 9.…”