A short-term assay of myeloid precursor cells in man

An assessment of the numbers of myeloid precursor cells in human bone marrow, obtainable earlier than with conventional colony assays, would be useful for many reasons. Recently an isotopic assay for murine-colony-stimulating activity has been devised and we have modified this technique for use in man. Bone marrow mononuclear cells are incubated in microtitre plates in the presence of optimal amounts of placental-conditioned medium, pulsed with 3H-galactose for 24 h and the isotope incorporation measured. Isotope uptake by normal bone marrow was found to be proportional to both the number of cells cultured and the amount of conditioned medium added. The cells responsible for isotope incorporation have been characterized partially and found to be nonadherent immature myeloid cells and have a density of less than 1.077. This short-term isotopic assay was also compared to the GM-CFC assay in ten normals and in 24 patients with either neutropenia (of different etiology), myeloid leukemias, or neutrophil leukocytosis. There was good correlation between the two assays in all the patients studied. Thus, our observations suggest that the cell incorporating 3H-galactose in response to conditioned medium has many of the properties of the GM-CFC and its immediate progeny. Although assay specificity has yet to be proven, our early results indicate that it may have use as a rapid, but indirect, assessment of human myeloid precursor cells and thus prove to be a useful adjunct to the standard hematological methods of assessment of certain patients.