The effects of chronic administration of cyclophosphamide on haemopoietic stem cells.

The effects of cyclophosphamide given for 18 weeks in small daily doses on CFU-S, CFU-C, and CFU-E content in mice bone marrow and spleen were studied. In the bone marrow, after an initial drop, the stem cell content rises above the normal values and remains there throughout a long period. In the spleen the stem cell content shows an initial several fold increase followed by a steady decline. It seems possible that this behaviour reflects a compensative effect to the toxic action of the drug at more differentiated levels of the haemopoietic cells.