Successful Gene Therapy in Utero for Lethal Murine Hypophosphatasia

Abstract

Hypophosphatasia (HPP), caused by mutations in the gene ALPL encoding tissue-nonspecific alkaline phosphatase (TNALP), is an inherited systemic skeletal disease characterized by mineralization defects of bones and teeth. The clinical severity of HPP varies widely, from a lethal perinatal form to mild odontohypophosphatasia showing only dental manifestations. HPP model mice (Akp2 -/ -) phenotypically mimic the severe infantile form of human HPP; they appear normal at birth but die by 2 weeks of age because of growth failure, hypomineralization, and epileptic seizures. In the present study, we investigated the feasibility of fetal gene therapy using the lethal HPP model mice. On day 15 of gestation, the fetuses of HPP model mice underwent transuterine intraperitoneal injection of adeno-associated virus serotype 9 (AAV9) expressing bone-targeted TNALP. Treated and delivered mice showed normal weight gain and seizure-free survival for at least 8 weeks. Vector sequence was detected in systemic organs including bone at 14 days of age. ALP activities in plasma and bone were consistently high. Enhanced mineralization was demonstrated on X-ray images of the chest and forepaw. Our data clearly demonstrate that systemic injection of AAV9 in utero is an effective strategy for the treatment of lethal HPP mice. Fetal gene therapy may be an important choice after prenatal diagnosis of life-threatening HPP.

Enzyme replacement for craniofacial skeletal defects and craniosynostosis in murine hypophosphatasia

“…Given early diagnosis, these results therefore support testing of recombinant TNAP enzymes for preventing or diminishing the severity of craniosynostosis in humans. I n utero delivery systems will be needed to prevent prenatal onset craniosynostosis in humans [47]. Studies investigating the long-term impact of enzyme replacement on the skull are also warranted.…”

Hypophosphatasia: diagnosis and clinical signs – a dental surgeon perspective

“…Spectacular improvements in terms of survival, skeletal manifestation (including healing of rickets), pulmonary function, and growth were reported when asfotase alfa was studied in young children with very severe perinatal or infantile HPP. Other treatments, such as other enzyme replacement therapy or even gene therapy, have also been investigated in animal models.…”

Prevention of Lethal Murine Hypophosphatasia by NeonatalEx VivoGene Therapy Using Lentivirally Transduced Bone Marrow Cells

“…This is noteworthy, as the plasma ALP level was sufficient to obtain therapeutic benefits without adverse effects, as we reported previously. [17][18][19] In both ALP-BMC-treated Akp2 -/-mice and the two surviving mock-BMC-treated Akp2 -/-mice, the engraftment of donor cells was maintained at approximately 30% throughout the experimental period (Fig. 1E), though only the ALP-BMCtreated Akp2 -/-mice experienced a therapeutic effect.…”

“…48,49 To develop a fetal treatment for perinatal HPP, we previously examined the effect of transuterine intraperitoneal injection of an AAV vector harboring the TNALP-D 10 construct into fetal Akp2 -/-mice on day 15 of gestation. 18 The fetal treatment provided preferential transduction of growth plate chondrocytes by AAV vector in the epiphysis of the treated Akp2 -/-mice. In utero transplantation of paternal hematopoietic stem cells was successfully applied to treat X-linked severe combined immunodeficiency.…”

“…14 Taking a different approach to treating HPP, we demonstrated that a single intravenous or intraperitoneal injection of a lentiviral or adeno-associated viral (AAV) vector encoding bone-targeted TNALP in which D 10 was linked adjacent to the C-terminus of soluble TNALP (TNALP-D 10 ) resulted in sustained expression of TNALP-D 10 and prevention of the disease phenotype in Akp2 -/-mice. [17][18][19] Viral vectormediated ERT should be more practical and economical than classic ERT, which requires repeated injection of purified recombinant enzyme. There are several concerns with this in vivo gene therapy, however, including the risk of inadvertent germline gene transfer 20,21 and induction of immune responses to the viral vector peptide or transgene product 22,23 after systemic or tissue-specific administration of the high-dose viral vector needed to achieve therapeutic benefits.…”