Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and nongenotoxic conditioning

Introduction: Autosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function. Most of the cases are due to TCIRG1 gene mutation, leading to severe bone phenotype and death in the first years of life. The standard therapy is the hematopoietic stem cell transplantation (HSCT), but its success is limited by several constraints. Conversely, gene therapy (GT) could minimize the immune-mediated complications of allogeneic HSCT and offer a prompt treatment to these patients.
Methods: The Tcirg1-defective oc/oc mouse model displays a short lifespan and high bone density, closely mirroring the human condition. In this work, we exploited the oc/oc neonate mice to optimize the critical steps for a successful therapy.
Results: First, we showed that lentiviral vector GT can revert the osteopetrotic bone phenotype, allowing long-term survival and reducing extramedullary haematopoiesis. Then, we demonstrated that plerixafor-induced mobilization can further increase the high number of HSPCs circulating in peripheral blood, facilitating the collection of adequate numbers of cells for therapeutic purposes. Finally, pre-transplant non-genotoxic conditioning allowed the stable engraftment of HSPCs, albeit at lower level than conventional total body irradiation, and led to long-term survival and correction of bone phenotype, in the absence of acute toxicity.
Conclusion: These results will pave the way to the implementation of an effective GT protocol, reducing the transplant-related complication risks in the very young and severely affected ARO patients.

引言：常染色体隐性成骨不全症（ARO）是一种罕见的遗传性疾病，其特征为由于破骨细胞功能缺陷导致的骨骼密度增加。绝大多数病例源于TCIRG1基因突变，导致严重的骨骼表型，并在生命的最初几年内死亡。标准治疗方法为造血干细胞移植（HSCT），但其成功率受到多种限制。相反，基因治疗（GT）可以最大限度地减少同种异基因HSCT的免疫介导并发症，并为这些患者提供及时的治疗。方法：Tcirg1缺陷型oc/oc小鼠模型表现出短暂的生存期和较高的骨骼密度，与人类状况密切相关。在本研究中，我们利用oc/oc新生小鼠优化了成功治疗的关键步骤。结果：首先，我们证明了慢病毒载体GT可以逆转成骨不全症的骨骼表型，实现长期存活并减少骨髓外造血。接着，我们展示了普利西法诱导的动员可以进一步增加外周血中循环的HSPC数量，从而便于收集足够数量的细胞用于治疗目的。最后，移植前非基因毒性预处理允许HSPC的稳定植入，尽管其水平低于传统全身照射，但无急性毒性，并导致长期存活和骨骼表型的校正。结论：这些结果将为实施有效的GT方案铺平道路，降低年轻且严重受影响的ARO患者的移植相关并发症风险。