Granulocyte-committed progenitor cells in the blood of patients with myelosclerosis.

Granulocyte-committed progenitor cells (colony-forming units, CFUc) in the blood of 10 patients with primary myelosclerosis and 2 patients with myelosclerosis following polycythaemia vera were assayed by the agar culture technique. The mean number of CFUc was 54.1 ± 109 (SD) (range 1.4–394) × 106/1 which corresponded to an increase of more than 1000-fold above normal levels. There was a linear relationship of CFUc with total leucocyte count in the different patients. The magnitude of this increase resembles that found in untreated patients with chronic granulocytic leukaemia and is therefore in keeping with the concept that the concentration of CFUc in the circulation is due to a primary increase in their number and not to disordered release from the marrow.