Competitive engraftment of adult and fetal murine hematopoietic progenitor cells following in utero transplantation

The engraftment potential of adult bone marrow and fetal liver hematopoietic progenitor cells was compared following transplantation into 13.5 day gestation NOD/LtSz-scW/J (Ly-5.2) mouse embryos. Donor cells were prepared from mice expressing Ly-5.1 alone (adult bone marrow; C57B1/6), or those co-expressing Ly-5.1 and Ly-5.2 (fetal liver; C57B1/6J × B6.SJL). Cells from fetal liver and bone marrow (6 months of age) were depleted of lineage-positive cells using immunomagnetic beads. Recipient embryos were injected with a maximum of 3ul of a solution containing equal numbers of fetal and adult cells (final concentration 4×10⁵ cells/ul). Four weeks after birth recipients were analyzed. Recipients were considered chimeric if > 0.5% of the cells in peripheral blood (PB) bone marrow (BM). or spleen were of donor origin. Ninety-two percent of recipients were chimeric in the spleen and 77% in the PB whilst only 38% were chimeric in the BM. Similar patterns of engraftment were found in both PB and spleen. Fetal liver-derived cells were found in 100% of the chimeric animals, whereas adult bone marrow engrafted in 60% of chimeric mice. The frequency of donor cells derived donor from fetal liver was 5-10 fold greater than that contributed from adult donor cells. Donor myeloid cells were present in the PB although lymphoid (T- and B) cells predominated in both PB and spleen. The bone marrow of engrafted recipients typically showed low levels of donor cells between 0.5 and 1%. These results clearly demonstrate that fetal liver-derived hematopoietic progenitor cells have a higher engraftment potential on a per cell basis than adult BM-derived progenitor cells. Ongoing secondary transplant studies will define the frequency of transplantable hematopoietic stem cells derived from fetal live and adult BM.