Membrane-Bound Human Stem Cell Factor Promotes Differentiation of Human Granulocytes and Mast Cells In Vivo,

Abstract 3419

Recently, advances in xenograft models for human hemamtopoietic stem cells (HSCs), or the humanized mice, have begun to allow investigators to examine the differentiation of human hematopoietic and immune cells in vivo. However, lymphoid-skewed human hematopoietic development in the mouse bone marrow is one of the remaining limitations in the humanized mouse models. The inefficient human myeloid development could at least partly be attributed to the mouse microenvironment not fully supporting differentiation and maturation of human myeloid lineage. To overcome this problem, we focused on the role of membrane-bound human stem cell factor in supporting the maintenance of human HSCs and inducing the development of human myeloid cells and created human stem cell factor transgenic NOD/SCID/IL2rgKO (hSCF Tg NSG) mice. Transplantation of 5000–50000 cord blood-derived Lin-CD34+CD38- cells resulted in significantly higher engraftment of human CD45+ leukocytes at 3–6 months post-transplantation in the bone marrow, spleen, and peripheral blood of hSCF Tg NSG recipients compared with those of non-transgenic NSG recipients. The enhanced human CD45+ engraftment was most prominent in the bone marrow (hSCF Tg recipients: 98.0 +/− 1.3%, n= 15, non-Tg NSG controls: 75.3 +/− 7.3%, n=7). In the bone marrow, the frequency of human CD33+ myeloid cells within the total human CD45+ population was significantly higher in the hSCF Tg NSG recipients than in the non-Tg NSG recipients and constituted the majority of human hematopoietic cells (hSCF Tg recipients: 54.6 +/− 4.5%, n=15 and non-Tg NSG controls: 29.3 +/− 4.0%, n=7). Flow cytometric analysis demonstrated that the majority of engrafted human myeloid cells in the hSCF Tg recipient bone marrow were side-scatter high, HLA-DR negative granulocytes. Reflecting the effect of human SCF on the development of human mast cells, human c-Kit+CD203c+ mast cells were identified in the bone marrow, spleen, and gastrointestinal tracts of the hSCF Tg NSG recipients. Altogether, the in vivo humanized mouse model demonstrates the essential role of membrane-bound SCF in human myeloid development. The hSCF Tg NSG humanized mice may facilitate the in vivo investigation of human HSCs, myeloid progenitors and mature myeloid lineage.