Clonal generation of multipotent and unipotent hemopoietic blast cell colonies in vitro

Colonies with a unique compact morphology and displaying high replating potential develop in methycellulose cultures when bone marrow cells from hydroxyurea- or 5-fluorouracil-treated mice are cultured in the presence of syngeneic thymocytes. These compact colonies are clonal, originating from a single unit, the compact-colony-forming unit (CFU). Based on replating analysis, at least three groups of compact colonies exist: (1) those that do not replate, (2) those that replate and give only GM colonies, and (3) those that give rise to granulocyte-macrophage (GM), erythroid (E), and mixed-erythroid (MIX/E) colonies. Colonies in the last group have a mean size of 2,060 cells and generate an average of 244 colonies in secondary cultures. Velocity sedimentation studies showed the compact-CFU to be similar in size to the MIX/E-CFU, sedimenting at rates between 3.5 and 7 mm/hour. In addition to giving rise to large numbers of in vitro CFU, compact-CFU are also able to generate day 8 spleen colony-forming units (CFU-S).