This clinical trial is focused on studying a condition known as Osteogenesis Imperfecta, often referred to as Brittle Bone Disease. This condition is characterized by bones that break easily, often with little or no apparent cause. The study specifically targets severe forms of this disease, including Osteogenesis Imperfecta type III and severe type IV. The treatment being tested in this trial involves the use of BOOST cells, which are a type of cell therapy made from allogeneic fetal mesenchymal stem cells. These cells are derived from the liver of a human fetus and are used in a solution that is administered through an infusion into a vein.

The purpose of this study is to evaluate the safety and tolerability of administering these stem cells to children and fetuses with severe forms of Brittle Bone Disease. Participants in the study will receive four doses of the BOOST cells, either after birth or both before and after birth. The study will compare the outcomes of these treatments with historical data and untreated controls. The trial aims to understand how safe the treatment is and how well it is tolerated by the participants.

Throughout the study, researchers will monitor the participants for any side effects related to the treatment. They will also track the number of bone fractures, the time it takes for a fracture to occur after the last dose, and changes in bone density and growth. The study will also look at changes in the clinical status of the disease and biochemical markers related to bone turnover. The trial is expected to continue until 2030, providing valuable insights into the potential benefits and risks of using BOOST cells for treating severe Brittle Bone Disease.