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CD 34 expression by murine hematopoietic stem cells mobilized by granulocyte colony-stimulating factor

Controversy has existed about CD34 expression by hematopoietic stem cells. We recently reported that CD34 expression reflects the activation state of stem cells by using a murine transplantation model. It has been generally held that mobilized blood stem cells express CD34.However, it has also been reported that mobilized stem cells and progenitors are in G0/G1 phases of the cell cycle. To address the state of CD34 expression by the mobilized stem cells, we again used the mouse transplantation model. We prepared CD342 and CD341 populations of nucleated blood cells from granulocyte colonystimulating factor–treated Ly-5.1 mice and assayed each population for long-term engrafting cells in lethally irradiated Ly5.2 mice. The majority of the stem cells were in the CD341 population. The CD34 expression by mobilized stem cells was reversible because re-transplantation of Ly-5.1 CD342 marrow cells harvested from the Ly-5.2 recipients of CD341-mobilized stem cells 8 months posttransplantation revealed long-term engraftment. These results may support the use of total CD341 cells in mobilized blood as a predictor for engraftment and CD34 selection for enrichment of human stem cells. (Blood. 2000;96:1989-1993)