Towards Gene Therapy of Osteopetrosis.

The goal in this thesis is development of gene therapy for malignant infantile osteopetrosis (IMO), a rare but severe genetic bone disease. The concept of osteopetrosis implies dysfunction or lack of osteoclasts, the bone resorbing cells in our body, resulting in failure of normal bone breakdown. Although involved in bone remodeling, osteoclasts are of hematopoietic origin and may potentially be targeted by genetic modification of hematopoietic stem cells (HSCs). Recently, clinical progress within the field of gene therapy has been achieved for other monogenic diseases affecting the hematopoietic system thereby providing hope for future clinical application also for osteopetrosis. We have been working with a mouse model of IMO called the oc/oc mouse and have been able to correct the otherwise lethal osteopetrotic phenotype in theses animals by transplantation of normal bone marrow. In addition, we established optimal pre-transplantation irradiation dose, cell dose and onset of treatment. Further studies in the oc/oc mouse model involved gene therapy where oc/oc fetal liver derived HSCs were transduced with a retroviral vector and subsequently transplanted into oc/oc mice. In vitro studies of osteoclast function revealed a partial restoration of bone resorbing activity. The osteopetrotic phenotype was reversed and this resulted in long-term survival of transplanted mice. The present findings provide a first and significant step towards the development of gene therapy in patients with malignant osteopetrosis. To prepare for human gene therapy, we also investigated the ability of lentiviral vectors, produced by stable packaging cell lines, to transduce human CD34+ SCID repopulating cells