Objective: By using a murine transplantation model, we studied the relationship between CD34 expression and expression of CD4 and Mac-1 by hematopoietic stem cells of normal adult mice.
Materials and methods: Cells from Ly-5.1 C57BL/6 mice were used as test cells and lethally irradiated Ly-5.2 mice were used as recipient mice. Peripheral blood was obtained 6 months posttransplantation to analyze engraftment of donor-derived cells.
Results: First, we determined that CD34- long-term reconstituting cells are CD4-, while some CD34+ stem cells express CD4. We then studied Mac-1 expression. Mac-1(-) and Mac-1(low) populations of both CD34- and CD34+ cells were capable of long-term reconstitution. Mac-1(high) population of CD34+ cells but not of CD34- cells also engrafted.
Conclusions: These results strongly indicate that depletion of Mac-1(+) and CD4(+) cells in stem cell purification may inadvertently discard significant populations of CD34+ stem cells. Since positive selection based on CD34 expression is the current practice for purification of human stem cells, our studies may possess implications in the purification of human hematopoietic stem cells.