Ultrasound-guided stem cell sampling from the early ovine fetus for prenatal ex vivo gene therapy

OBJECTIVE: Prenatal ex vivo gene therapy might be an effective and safe strategy with which to treat severe genetic disorders in utero. For this purpose, autologous fetal stem cells must be collected before the second trimester, transfected in vitro, and transplanted back to the fetus. The aim of this study was to determine whether stem cells can be sampled from the first trimester fetal liver in ongoing gestation. STUDY DESIGN: Fetal liver stem cell sampling was performed in 21 ovine fetuses, Pregnant ewes at 57 +/- 2 gestational days were generally anesthesized. A 20-gauge needle was inserted transcutaneously into the fetal liver under ultrasound guidance. Fetal liver cells were sampled by suction. The numbers of nucleated cells and progenitor/stem cells were determined. RESULTS: All 21 fetuses showed normal heart rate 5 minutes after the procedure. A mean (+/- SEM) of 2.07 +/- 0.5 X 10(7) nucleated cells and 172 +/- 53 colony-forming units per 10(5) cells (hematopoietic progenitors/stem cells) were collected. Fetal loss rate at term was 7 of 21 fetuses (33%). CONCLUSION: This study shows that fetal liver cells can be collected in the early fetus with an ultrasound-guided technique. The number of fetal liver cells that are collectable is large enough for autologous transplantation and engraftment of genetically engineered (transfected) stem cells.