Two classes of primitive pluripotent hemopoietic progenitor cells: Separation by adherence

Methylcellulose cultures containing mouse marrow cells at low densities and partially purified preparations of erythropoietin and Interleukin‐3 were scored after 2 weeks for the presence of macroscopic multilineage colonies (from “primary” CFU‐macro GEMM). Whole cultures were then harvested and replated to assess the number of “secondary” CFU‐macro GEMM produced, but not detected, during the primary culture period. In such experiments adherent marrow cells yielded significantly higher numbers of secondary CFU‐macro GEMM than did either fresh or nonadherent marrow cells. Removal of macroscopic colonies prior to replating showed that most secondary CFU‐macro GEMM were not derived from primary CFU‐macro GEMM. In vivo studies also revealed a differential effect of adherence separation on the frequency of day 10 CFU‐S, which decreased, by comparison to cells capable of long‐term repopulation, which increased. Primary adherent CFU‐macro GEMM from 5‐fluorouracil (5‐FU) treated mice showed an 18‐fold higher self‐renewal capacity than their counterparts in normal marrow. Nevertheless the majority of secondary CFU‐macro GEMM obtained from primary cultures of adherent 5‐FU cells were again not derived from primary CFU‐macro GEMM. Cells capable of immediately generating large multilineage colonies thus appear to represent an intermediate compartment of pluripotent progenitors whose self‐renewal properties, may, however, vary over a considerable range. Our results further suggest that these progenitors are derived ultimately from a more primitive adherent cell whose tendency to begin to divide in vitro is low and whose presence correlates with cells capable of long‐term myeloid repopulation in vivo.