Pre-clinical therapeutics for osteopetrosis caused by PLEKHM1 deficiency Using ex Vivo and in vivo gene Therapies.

Background: Osteopetrosis caused by mutation of Plekhm1 gene is characterized by malignant phenotypes, poor quality of life, and lack of effective treatment. It remains in dispute whether hematopoietic stem cell transplantation (HSCT) is a suitable therapeutic approach for it. In addition, other potential novel therapeutics including gene therapies have not yet been investigated for their efficacies.

Materials And Methods: We generated an osteopetrotic mouse model caused by deficiency of Plekhm1 gene, and performed HSCT, ex vivo and in vivo gene therapies, respectively.

Results: A notable reduction of femoral trabecular bone mass, along with osteoporosis, was observed after HSCT treatment for 12 weeks. For ex vivo gene therapy, HSCs of KO mice were explanted, transferred by LV- Plekhm1 , and reinfused into KO mice. After 12 weeks, osteopetrosis of Plekhm1 KO mice was also improved significantly. In vivo gene therapy was performed by injecting AAV- Plekhm1 into left tibial bone marrow cavity of KO mice. A significant reduction in the trabecular area of the left femora of Plekhm1 KO mice 12 weeks after treatment with AAV- Plekhm1 was observed.

Conclusion: Both HSCT, ex vivo and in vivo gene therapies showed good safety profiles, which provides promising therapeutic approaches to potentially rescue the osteopetrotic phenotype in patients with a Plekhm1 gene mutation.