Plastic-adherent cells in human bone marrow generate long-term hematopoiesis in vitro

This study demonstrates that the human bone marrow mononuclear cell fraction that adheres to plastic during a 2-h incubation period includes stromal precursors and hematopoietic progenitor cells that can sustain hematopoiesis for at least 5 weeks in a long-term culture (LTC) system. Delta (delta) assays were performed on the 2-h plastic-adherent fraction of mononuclear cells, by assaying the numbers of CFU-GM released into the culture supernatant during 1 week of incubation, to investigate the properties of the original progenitor cells. The plastic-adherent delta (P delta) progenitor cells all express CD34, and a variable proportion express Thy-1. The numbers of CFU-GM produced are directly related to the numbers of mononuclear cells used to initiate the cultures, and limiting dilution experiments indicate a frequency for P delta cells of 2.5-10/10(5) mononuclear cells. The numbers of CFU-GM produced by individual P delta cells at limiting dilution vary considerably within experiments but the distributions of CFU-GM per P delta progenitor show little variation between samples. On average, P delta cells generate 6-9 early CFU-GM scored on day 21 of culture; 10-23 CFU-GM scored on day 14, and 18-40 mature CFU-GM scored on day 7. These results show that plastic-adherent cells in human bone marrow are capable of sustained hematopoiesis in vitro and of producing a spectrum of clonogenic progeny. They form the basis of an assay for investigating the kinetics of early human hematopoietic progenitor cells.