Enrichment of Early Fetal‐Liver Hemopoietic Stem Cellsof the Rat Using Monoclonal Antibodies Against theTransferrin Receptor, Thy‐1, and MRC‐Oχ82

Fetal livers from inbred rat fetuses at 14 days' gestation were dispersed into a single-cell suspension by physical disruption and collagenase digestion. Pluripotent stem cells were characterized and partially purified by a combination of monoclonal antibodies. These included CD71 (anti-transferrin receptor, MRC-OX26, used for rosetting), Cdw90 (anti-Thy-1, MRC-OX7), and the newly described MRC-OX82 (reacting with myeloiid cells in peritoneal exudate), employed in FACS sorting. Enrichment was monitored by long-term reconstitution of lethally irradiated congenic rats genetically distinguishable from the donor by an allelomorphic variant of the CD45 cell-surface antigen. At intervals from 3 months to 1 year, lymph-node cells and peritoneal exudate cells were biopsied for analysis by two-color flow cytometry--one color to determine donor origin, the other to identify Th cell (CD4+), Tc cell (CD8+), B cell (sIg+ or CD45RC+), neutrophil (OX82+ or OX43-), and macrophage (OX43+) compartments. The degree of chimaerism was taken as the read out of stem-cell activity. No significant differentials between lymph-node and peritoneal exudate chimaerisms were detected in any of the recipients; therefore, the enrichment procedure revealed only pluripotent cells, not stem cells of restricted potency. All recovered stem-cell activity was in the OX26(CD71)-negative, OX7(CDw90)-positive, OX82-positive fraction. In the optimum case, an enrichment of very roughly 200-fold in cell-for-cell activity was obtained. Rat bone-marrow colony-forming units in the spleen (CFUs-12) were found to lack the surface antigens recognized by the monoclonal antibodies CD53 (MRC-OX44), MRC-OX39, MRC-OX59, and 144.2.15. These would provide a strategy for their enrichment by depletion.