Genetic editing and cell therapy for correction of CLCN7 mutations in osteopetrosis

Project Summary: Osteopetrosis is a heritable skeletal disorder characterized by abnormal systemic increase in bone mass density, bone marrow failure, bone fractures, osteomyelitis, and impaired vision and hearing, among other clinical features leading to physical disability and death of patients. Osteopetrosis can be caused

by mutations in the Clcn7 gene that result in defects in the function of osteoclasts (OCs), tissue resident cells of the bone derived from hematopoietic progenitors and specialized in bone resorption. Bone marrow transplantation (BMT), which replaces defective OCs and restores bone resorption is the only available treatment

for osteopetrosis despite knowing its etiology for decades. However, not all patients are eligible for BMT, depend on HLA-match donors, and patients who receive BMT frequently suffer from severe complications including toxicity of conditioning treatment, graft versus host disease (GVHD), among others, which results in high

transplant-related mortality. Alternative therapies for osteopetrosis have been reported that include genetic therapy using retroviral infection for delivery, unfortunately clinical trials showed elevated incidence of vector- induced hematological malignancies in these patients. Others have reported a therapeutic approach, currently

in clinical trials, that utilizes lentiviral infection in cells to provide with functional genes followed by transplantation, however, this therapy requires conditioning treatment including irradiation or chemotherapy to achieve engraftment of genetically modified cells. In this grant, we proposed a novel alternative therapeutic strategy that combines CRISPR/Cas9-based genome

editing tools to correct osteopetrosis-causing Clcn7 mutations ex vivo in hematopoietic progenitors, followed by autologous infusion of mutation-corrected cells into osteopetrotic mice to restore normal bone remodeling. This novel approach overcomes the undesired long term and fatal consequences of BTM, since it does not require

HLA-match donors and conditioning treatment including irradiation or chemotherapy for cell engraftment. The goal of this grant is to develop and establish standard protocols for the assessment, design, testing and validation of CRISPR/Cas9 genome editing technologies that would offer individual patients with a mutation-specific and

cell-specific approach to treat osteopetrosis.