Infants<18 months of age (originally<12 months) and singleton pregnant women whose fetus has severe OI with confirmed glycine substitution in <i>COL1A1</i> or <i>COL1A2</i> can be included in the trial.Each subject receives four intravenous doses of 3×10<sup>6</sup>/kg BOOST cells at 4 month intervals, with 48 (doses 1-2) or 24 (doses 3-4) hours in-patient follow-up, primary follow-up at 6 and 12 months after the last dose and long-term follow-up yearly until 10 years after the first dose. The gene discussed is COL1A2; the disease is osteogenesis imperfecta.