AAV Gene Therapy for MPS1 Corneal Clouding and Joint Stiffness

Mucopolysaccharidosis type 1 (MPS1), also known as Hurler syndrome, is a genetic lysosomal storage disease that results from the loss-of-function mutations present on the L-iduronidase (IDUA) gene. As a consequence, glycosaminoglycans accumulate aberrantly in lysosomes in multiple organs, leading to hepatosplenomegaly, dwarfism, mental and psychomotor retardation, life-threatening cardiac and pulmonary complications, several skeletal and ocular manifestations and nervous system problems. Untreated pediatric patients often die at 5-10 years of age from progressive heart and lung involvement. Since the early 1980s, successful treatment of MPS1 patients with allogeneic hematopoietic stem cell transplantation after myeloablative chemotherapy has been established. The benefits of this therapy rely on cross-correction of IDUA deficient cells with functional IDUA protein produced by a donor cell circulating through the blood and also from engraftment of donor-derived glial cells in the MPS1 patient brain. As a result, if the stem cell transplantation is performed before two years old, the individual manifests cardiac, liver, pulmonary and neurological improvement as well as his lifetime is significantly prolonged. However, still >30% of the patients have progressive corneal clouding, which leads to blindness. Cornea transplantation is not an option for patients with severe hurler disease and the ones that receive a cornea transplant are at the risk of developing future cloudiness. Recently, we have developed an adeno-associated virus (AAV) capable of delivering idua cDNA to MPS1 patient fibroblasts and human corneas and restoring IDUA protein function. Furthermore, immunohistochemistry analysis of intrastromal IDUA protein in a normal human cornea showed low levels of the protein. Even though the levels of IDUA that are required to correct the loss of sight in MPS1 patients are relatively small, administration of a >50-fold increase in IDUA activity (over wild type levels) with gene therapy does not result in any detectable cellular toxicity. We then investigated AAV serotype tropism by incubating human cornea with different AAV viral capsids carrying AAV-CMV-eGFP. From this experiment, we have identified certain capsids with higher levels of transduction and GFP expression on the human cornea. Moreover, we determined the optimal injection volume required for complete coverage of the corneal center area, which is sufficient for allowing regain of the vision. Considering that: 1) the eye is an easily accessible, immune-privileged organ; 2) intrastromal injections are commonly performed in the clinic to treat fungal keratitis; 3) gene therapy for eye diseases has been performed for nearly two decades, and 4) there are 127 registered clinical trials currently taken place for gene therapy in the eye; we foresee that injection of AAV delivering idua cDNA directly to the cornea will likely reverse the MPS1-associated vision loss. Studies are underway to administrate the therapy to the MPS1 dog model for testing safety and efficacy. Furthermore, due to the success of the developed therapy to reestablish IDUA normal levels in cornea, we are currently focusing on the treatment of joint stiffness. We have identified a novel AAV serotype with the highest levels of transduction of the mouse and equine joint tissue explants as well as in cultured monolayers. We foresee that a combined administration of cord blood stem cells at the Carolinas Cord Blood Bank-Duke University and localized AAV-IDUA cDNA delivery to the human cornea and joint tissue at UNC will result in a significant improvement in quality of life of patients with Hurler disease.