Hematopoietic Stem Cell-Targeted Neonatal Gene Therapy with a Clinically Applicable Lentiviral Vector Corrects Osteopetrosis in oc/oc Mice

• Published in: Human gene therapy Vol. 30; no. 11; p. 1395
• Main Authors: Löfvall, Henrik, Rothe, Michael, Schambach, Axel, Henriksen, Kim, Richter, Johan, Moscatelli, Ilana
• Format: Journal Article
• Language: English
• Published: United States 01.11.2019
• Subjects: Animals; Animals, Newborn; Bone Resorption - pathology; Genetic Therapy; Genetic Vectors - metabolism; Hematopoietic Stem Cell Transplantation; Hematopoietic Stem Cells - cytology; Humans; Lentivirus - genetics; Mice; Osteoclasts - pathology; Osteopetrosis - genetics; Osteopetrosis - therapy; Phenotype; Promoter Regions, Genetic - genetics; Spleen - pathology; Survival Analysis; Vacuolar Proton-Translocating ATPases - genetics; osteopetrosis; TCIRG1; gene transfer to hematopoietic stem cells; lentiviral vectors; oc/oc
• ISSN: 1557-7422
• DOI: 10.1089/hum.2019.047

Infantile malignant osteopetrosis (IMO) is an autosomal recessive disorder characterized by nonfunctional osteoclasts. Approximately 50% of the patients have mutations in the gene, encoding for a subunit of the osteoclast proton pump. Gene therapy represents a potential alternative treatment to allogeneic stem cell transplantation for IMO. The mouse is a model of IMO characterized by a 1,500 bp deletion in the gene, severe osteopetrosis, and a life span of only 3 weeks. Here we show that the osteopetrotic phenotype in mice can be reversed by hematopoietic stem cell-targeted gene therapy with a clinically applicable lentiviral vector expressing a wild-type form of human under the mammalian promoter elongation factor 1α short (EFS-hT). c-kit fetal liver cells transduced with EFS-hT were transplanted into sublethally irradiated mice by temporal vein injection 1 day after birth. A total of 9 of 12 mice survived long term (19-25 weeks) with evidence of tooth eruption, uncharacteristic of mice. Splenocytes were harvested 19-25 weeks after transplantation and differentiated into osteoclasts on bone slices to assess resorption and on plastic to assess TCIRG1 protein expression. Vector-corrected osteoclasts showed human TCIRG1 expression by Western blot. CTX-I release relative to that mediated by -derived osteoclasts increased 8-239-fold. Resorption pits on bone slices were observed for osteoclasts derived from 7/9 surviving transplanted mice. Histopathology of the bones of surviving animals showed varying degrees of rescued phenotype, the majority with almost full correction. The average vector copy number per cell in the bone marrow was 1.8 ± 0.5. Overall, 75% of transplanted mice exhibited long-term survival and marked reversal of the osteopetrotic bone phenotype. These findings represent a significant step toward the clinical application of gene therapy for IMO.