The biology and ethics of banking fetal liver hematopoietic stem cells for in utero transplantation

Abstract

Background/Purpose: Transplantation of fetal liver hematopoietic stem cells (HSCs) in utero has the potential to treat a variety of hematologic, immunologic, and metabolic diseases. One prerequisite for broad clinical application is the establishment of a bank of fetal liver HSC tissue. The authors describe their methods for processing fetal liver free of known human pathogens while maximizing HSC activity after cryopreservation. Methods: The authors developed a protocol that separates the abortion decision from the donation decision and preserves confidentiality between donor and recipient. Human fetal livers (12 to 14 weeks' gestation) were procured from aborted specimens and the light-density hematopoietic cells isolated by density centrifugation. Total viable cell count increased with gestational age and averaged from 4.36 × 10 7 cells for 12-week livers to 2.0 × 10 8 cells for 14-week livers. Results: Flow cytometric analysis demonstrated the presence of early progenitors in fresh and thawed specimens and a low number of T cells in each group. The functional capacity of fetal liver progenitors was assessed with colony-forming assays before and after cryopreservation. Thawed specimens showed an average 63% recovery rate for the high-proliferative potential colony-forming cells, a primitive subset of progenitors thought to include HSC. However, the more mature fraction of low-proliferative potential colony-forming cells had a recovery rate of only 35%. These data suggest that fetal liver HSC maybe more resistant to the detrimental effects of cryopreservation than mature progenitors. The fetal liver was screened for bacterial, fungal, and viral contaminates and the serum from donor mothers was screened for human immunodeficiency virus (HIV), hepatitis A, B, and C, human T-cell lymphoma virus (HTLV I II ), rapid plasma reagent (RPR), cytomegalovirus (CMV), and toxoplasmosis IgM. The bacterial contamination rate was 14% (n = 28). The maternal serum was positive for CMV in 78% of cases, and positive for hepatitis C in 0.7% of cases (n = 28). However, all fetal liver specimens were culture negative for CMV. Conclusions: These findings demonstrate that human fetal liver HSCs can be procured ethically and processed to ensure a safe graft with a small number of T-cells, and a high yield of progenitors after cryopreservation. A bank of fetal liver HSC will prove useful in treating a variety of genetic diseases before birth by in utero HSC transplantation.