Successive stimulation of major cell groups in bone marrow. A preliminary approach to the problem of stem cell competition.

The existence of pluripotential haemopoietic stem cells raises the possibility of stem cell competition when two or more differentiating stimuli are given either simultaneously or in close succession. The experiments now reported deal with the effects on guinea pig bone marrow of successive stimulation and they fall into two groups. In one group, erythropoiesis was first stimulated by means of hypoxia, after which granulopoiesis was stimulated by the intraperitoneal injection of typhoid vaccine. In another group, these two stimuli were given in the reverse order. Bone marrow changes were evaluated both quantitatively and by differential counts. The experimental animals were compared with controls given only one stimulus, either hypoxia or vaccine, and also with normal untreated animals. As judged by the output of granulocytes or erythrocytes, no stem cell shortage developed in the experimental animals. A marked fall in transitional cells in the bone marrow of the experimental animals is consistent with the view, though not affording actual proof, that the pluripotential stem cells are to be found in the transitional cell compartment.