Cytokine treatment of hematopoietic stem/progenitor cells induces a homing defect in nonmyeloablated hosts

In a bone marrow transplant the selective translocation of stem cells from the blood to the bone marrow is called Homing. This process and the factors that influence it play an important role in the success of bone marrow transplants. Previous data in mice has shown that the majority of the cells capable of long term engraftment have entered S-phase by 12 hrs post infusion (Nilsson, Blood, 90, 1997). In related studies, whole bone narrow cells cultured in IL-3, IL-6, IL-11 and steel factor for 48 hrs have a profound engraftment defect up to 6 months post transplant. Engraftment was lost in late S/ early G2 and regained again in G1. These data indicate two things. First, the importance of cell cycle and second, the necessity to evaluate the homing of cells less than 24 hrs post transplant due to the rapid induction of cell cycle after transplant. We have now evaluated the homing of lineage negative Sca+ C57BL/6 marrow cells when cultured in IL-3, IL-6, IL-11 & steel factor for 48 hrs. Noncultured cells and cells cultured for 48 hours in cytokines were labeled with the fluorescent dye 5,6-carboxyfluorescein succinimidyl ester (CFSE). In previous studies, we have shown that by 3 hrs homing of these cells has plateaued. Thus we have examined the homing of 250000 control or cytokine treated Lin-Sca+ CFSE labeled cells 3 hrs after tail vein infusion. Host marrow cells were analyzed by FACS, for the presence of CFSE positive cells. In 5 experiments a range of 16 to 25 million events (cells) per animal was analyzed. These data indicate after 48 hours of cytokine exposure the number of positive donor stem cells seen in the host marrow 3 hrs post transplant is about 5 times less than that that of unmanipulated cells. These data indicate that the long term engraftment defect seen after stem cell exposure to cytokines is due to the induced presence of a homing defect.