Differential characterization of colony-forming units in diffusion chambers from pluripotent stem cells and progenitors of granulocytes/macrophages.

: Colony-forming units in diffusion chambers (CFU-D), pluripotent stem cells (CFU-S) and colony-forming units in agar cultures (CFU-C) were studied in the bone marrow of weanling mice injected twice with hydroxyurea (HU). CFU-D, CFU-S and CFU-C were assayed 2 h, 2 days and 4 days after HU administration. After 2 h the total number of CFU-D/femur marrow cells did not change, while CFU-S and CFU-C decreased to 16.6 and 13.5% of control levels, respectively. On Day 2, CFU-D and CFU-S increased to 25 and 16.6%, respectively, above control levels and CFU-C was only 52% of the normal level. Four days after HU administration, CFU-S decreased steeply to 7.6%, CFU-D 80% and CFU-C to 32% of their pretreatment levels. Bone marrow of HU-treated weanling mice was also incubated in liquid medium where CFU-S decreased more rapidly than did CFU-D. It is concluded that CFU-D in weanling mice represent a noncycling and more primitive stem cell pool than CFU-S and probably constitute a reserve pool, the mobilization of which is secondary to that of CFU-S.